# Foliar dewdroplet-induced redox cascades promote early flowering in Brassicaceae plants

Yu Zheng, Bolei Chen, Chun Bao, Yu Xia, Changli Zeng, Maoyong Song, Jianbo Shi, Ligang Hu, Yongguang Yin, Xiaoyun Cui, et al.

► To cite this version:

Yu Zheng, Bolei Chen, Chun Bao, Yu Xia, Changli Zeng, et al. Foliar dewdroplet-induced redox cascades promote early flowering in Brassicaceae plants. Proceedings of the National Academy of Sciences of the United States of America, 2026, 123 (8), pp.e2527021123. 10.1073/pnas.2527021123. hal-05517103

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Submitted on 18 Feb 2026

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Main Manuscript for

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Foliar Dewdroplet-induced Redox Cascades Promote Early Flowering
in Brassicaceae Plants

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Yu Zheng<sup>a,†</sup>, Bolei Chen<sup>b,†*</sup>, Chun Bao<sup>a</sup>, Yu Xia<sup>a</sup>, Changli Zeng<sup>a</sup>, Maoyong Song<sup>b</sup>, Jianbo Shi<sup>b</sup>,

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Ligang Hu<sup>b</sup>, Yongguang Yin<sup>b</sup>, Xiaoyun Cui<sup>c</sup>, Juline Auverlot<sup>d</sup>, Jean-Philippe Reichheld<sup>d</sup>, Guibin

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Jiang<sup>b</sup>, Yong Liang<sup>a*</sup>, Daoxiu Zhou<sup>c*</sup>, Richard N. Zare<sup>e*</sup>

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<sup>a</sup>Hubei Key Laboratory of Environmental and Health Effects of Persistent Toxic Substances, School of Environment and Health, Jianghan University, Wuhan, 430056, China.

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<sup>b</sup>State Key Laboratory of Environmental Chemistry and Toxicology, Research Center for Eco-environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China.

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<sup>c</sup>Institute of Plant Science Paris-Saclay, CNRS, INRA, Université Paris-Saclay, 91405 Orsay, France.

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<sup>d</sup>Laboratoire Génome et Développement des Plantes, CNRS, Université Perpignan, Via Domitia, 66860 Perpignan, France.

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<sup>e</sup>Department of Chemistry, Stanford University, Stanford, CA 94305, USA.

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*Bolei Chen https://orcid.org/0000-0001-8552-3334; Yong Liang https://orcid.org/0000-0002-

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3718-0987; Daoxiu Zhou https://orcid.org/0000-0002-1540-0598; Richard N. Zare

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https://orcid.org/0000-0001-5266-4253

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Email: blchen@rcees.ac.cn; ly76@263.net; dao-xiu.zhou@universite-paris-saclay.fr;

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zare@stanford.edu

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**Author Contributions:** Y. Z and B. C. contributed equally to this paper. Conceptualization: B. C.,

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Y. L., Y. Z.; Methodology: Y. Z., C. B., Y. X., X. C., B. C.; Investigation: Y. Z., C. Z., M. S., J. S., L.

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H., Y. Y., J-P. R., G. J., D. Z., Y. L., R. N. Z., B. C.; Visualization: B. C., Y. Z.; Funding

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acquisitions: J. S., M. S., Y. Y., J. A., J-P. R., G. J., D. Z., Y. L., R. N. Z., B. C.; Project
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administration: Y. Z., B. C.; Supervision: D. Z., Y. L., R. N. Z., B. C.; Writing – original draft: B.

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C., Y. L., Y. Z.; Writing – review & editing: B. C., Y. Z., D. Z., R.N. Z.

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**Competing Interest Statement:** The authors declare no competing interests.

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**Classification:** Chemistry; Plant Sciences

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**Keywords:** Microdroplets, Dew, Redox Cascades, S-Nitrosylation, Early Flowering

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**Abstract**

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Atmospheric water inputs such as dew are often overlooked in plant biology. We show that foliar dewdrops act as biochemical microreactors that trigger flowering in *Arabidopsis thaliana*, a small plant from the mustard family (*Brassicaceae*). These droplets generate reactive oxygen species that induce intracellular nitric oxide accumulation, initiating a redox cascade that suppresses the biosynthesis of abscisic acid, which contributes to the regulation of flowering time. This occurs via S-nitrosylation-mediated activation of histone deacetylase 19, which silences *AAO3* and *ABA2*.

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Analysis of over 12 million field records across the *Brassicaceae* family reveals a global correlation between dew point temperature and flowering time. These findings identify dewdrop chemistry as an unrecognized environmental cue that regulates developmental timing in plants.

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## Significance Statement

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Water microdroplets are regarded as microreactors capable of generating various reactive species, including reactive oxygen species (ROS), at their interfaces. Numerous studies have demonstrated that interfacial radical processes in microdroplets can mediate a variety of redox reactions. However, our understanding of the impact of microdroplet chemistry on the natural world remains limited. This study reveals that during dew formation on *Arabidopsis thaliana* leaves, radical cascade reactions occur within the micro-dewdrops on leaf trichomes, influencing the synthesis of abscisic acid and thereby promoting early flowering. Globally, changes in dew point temperature affect the flowering events of *Brassicaceae* plants. Against the backdrop of global warming, these findings enhance our comprehension of the advanced timing of plant flowering. More importantly, this research presents a case in which a microscopic interfacial chemical reaction within droplets influences macroscopic events in the natural world.

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## Main Text

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## Introduction

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Flowering is a critical phenological event in the plant life cycle, governed by complex interactions among environmental cues such as photoperiod and temperature (1-4). While increasing evidence shows that global warming is shifting plant phenology by days or even weeks (5, 6), these changes cannot be fully attributed to photoperiod, which remains seasonally fixed, or to direct thermal stress, given that global temperatures have risen only about 0.5 °C over the past 30 years (7). A more fundamental yet often overlooked consequence of global warming lies in its effect on atmospheric moisture dynamics (8). According to the Clausius-Clapeyron relationship, the water-holding capacity of near-surface air increases by roughly 7% per Kelvin, altering the formation and distribution of nonrainfall water sources such as dew (9, 10). Dew is a key pathway for atmospheric water to return to ecosystems. In early-leafing plants, microdroplets preferentially condense on leaf surfaces, particularly on trichomes, during spring, when diurnal temperature fluctuations are more pronounced (11).

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Recent studies reveal that both microdroplet condensation on solid surfaces and water-solid contact can spontaneously generate reactive oxygen species (ROS) (12-17), which are well-known regulators of plant development through signaling and epigenetic mechanisms (18-20). This raises the intriguing possibility that dewdrops may influence phenological transitions such as flowering. However, the specific chemical reactions occurring within these leaf-associated microdroplets, and their broader implications for plant
metabolism and development, remain largely unexplored. Here, we investigate the chemical nature of dewdrops on Arabidopsis leaves and their potential role in triggering flowering.

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## 80 Results and Discussion

### 81 Observing Dew-Driven Flowering.
Flowering and meteorological data of *Arabidopsis thaliana* in the wild from March to May in 2021 and 2022 in the Utrecht region of the Netherlands were collected and analyzed as shown in Fig. 1a. We operationally defined dew events as periods when ground surface temperature dropped below the dew point, indicating the presence of dew condensation. Flowering consistently followed such dew condensation events in March and May 2021 and again in May 2022, although the specific dates of floral transition varied between years. Importantly, by restricting observations to the March-May window, we averaged the relatively constant photoperiod to uncover additional factors influencing flowering behavior that are often masked by its dominant seasonal effect. While average air temperatures fluctuated slightly across the observation periods, temperature alone was unlikely to account for the observed flowering dynamics. To assess whether this association extended beyond local conditions and individual years, we expanded our analysis to include nationwide records of *Arabidopsis thaliana* flowering phenology and meteorological data spanning 2004 to 2023 (Fig. S1). Remarkably, 50.4 % of all documented flowering events occurred within one week following a dew condensation period as shown in Fig. 1b. This temporal coupling between dew and floral initiation supports the hypothesis that dew may serve as a previously underrecognized environmental cue for flowering, which raises the possibility that condensation-driven microdroplet chemistry could play a functional role in plant development.

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### 99 NO Generation in Foliar Dewdroplet.
To investigate the chemical processes occurring within micro-dewdrops on *Arabidopsis thaliana* leaves, we developed an experimental model that mimics natural condensation. Given that microdroplets preferentially form at the surface of trichomes during dew formation, we manually placed microdroplets on these structures to replicate the spatial distribution of natural dew (Fig. 2a, 2b and Fig. S2). We introduced a water-soluble ROS-sensitive probe, 10-acetyl-3,7-dihydroxyphenoxazine into the microdroplets. As shown in Fig. 2c and Fig. S3, strong fluorescence signals indicated spontaneous ROS generation within the micro-dewdrop condensates found on trichomes. Additionally, Fig. S4 indicates that the micro-dewdrops on the trichomes will disappear along with the evaporation process of water, and the related ROS fluorescence signal also disappears accordingly. To determine the source of the fluorescence signals, we placed plant leaves in an environmental simulation chamber, controlled the leaf temperature below the dew point, collected the condensate from the leaf surfaces, and allowed it to react with free radical trapping agents to indirectly analyze the types of free radicals in the micro-dewdrops. As shown in Fig. S5, the fluorescence signals that we observed from the micro-dewdrops originate from hydroxyl radicals. Since ROS are essential for
plant growth, the ROS observed in micro-dewdrops may act as a signaling molecule for growth regulation (21).

To explore downstream chemical transformations, we detected the presence of nitric oxide (NO), a key signaling molecule in plants (21), using a NO-specific fluorescent probe (3-amino, 4-amionmethyl-2',7'-difluorescein, diacetate, DAF-FM DA (A nonfluorescent compound that can react with NO to produce a fluorescent product). As shown in Fig. 2d and Fig. S6, NO generation was observed in microdroplets on the leaf surface. This NO may be generated from reactions between ROS and amine, amide, or nitrite groups present on the surface of trichomes (shown in Fig. S7) (22, 23). These findings suggest that the condensation of atmospheric water can initiate a cascade of redox chemistry on the leaf surface, including the formation of NO, with potential implications for signal transduction in plants. This observation prompts a fundamental question: can these extracellular chemical processes, triggered by dew condensation, influence intracellular biochemical processes?

**Potential Mechanism of Flowering Promotion by Dew.** To explore this, we cultivated *Arabidopsis thaliana* plants on culture media in a controlled-environment chamber maintained at 28 °C with 90 % relative humidity. Under these conditions, the leaf surface temperature stabilized at 25.5 °C (Fig. S8), below the dew point, resulting in persistent condensation on the leaf surface. After 24 hours of dew exposure, we analyzed NO accumulation in guard cells using DAF-FM DA, which can cross the cell membrane and react with intracellular NO. As shown in Fig. S9, the fluorescence intensity of NO in the guard cells of dew-exposed leaves was much higher than that in leaves without dewdrops. We suggest that NO likely enters the leaf primarily via diffusion through stomata, while the cuticular wax layer presents a significant barrier to its penetration. Consistent with this localized observation, we detected a significant increase in seedling NO content following dew exposure (Fig. 2e), whereas the activity of nitric oxide synthase (NOS) remained unchanged between dew-treated and untreated control samples (Fig. 2f). It should be noted that NOS activity was measured using a commercial kit based on the L-arginine reaction to generate NO and L-citrulline. These results indicate that micro-dewdrops on the leaf surface chemically elevate NO levels in leaf cells.

It is well established that NO-related signaling pathways involve S-nitrosylation of proteins of a wide range of physiological activities in plants (24-26), including the histone deacetylase HDA19 that is involved in the regulation of flowering time (27-30). HDA19 is present in both cytoplasm and nucleus and appears in two different protein complexes in native nonreducing gels (Fig. S10). Interestingly, dew exposure increases molecular masses (MM) of the HDA19 complexes in both cytoplasm and nucleus (Fig. S8). Analysis of the HDA19 protein complexes by mass spectrometry identified several peptides of the glutaredoxin GRXS17 (Fig. S11), suggesting that the complexes comprise GRXS17. Co-immunoprecipitation (Co-IP) assays confirmed that HDA 19 interacts with GRXS17 (Fig. S12).
GRXS17 is also a NO target (Fig. S13). At the cellular level, dew exposure led to an increase in NO levels in the cell (Fig. 3a). Similarly, the interaction between HDA19 and GRXS17 in the nucleus was highly enhanced after dew exposure. To investigate the relationship between NO and the proteins, we generated the complementation plants by transforming tagged GRXS17 and HDA19 into their respective loss-of-function mutants (which display early flowering) (28, 29). As shown in Fig. 3b and Fig. S14, the tagged HDA19 and the GRXS17 proteins exhibit enhanced S-nitrosylation in complementation lines under dew exposure. In GRXS17 mutant background, S-nitrosylation of HDA19 was undetectable. By contrast, HDA19 mutation has no effect on S-nitrosylation of GRXS17. Furthermore, GRXS17 displays a higher NO-binding rate than HDA19 (Fig S15a) and can mediate S-nitrosylation of HDA19 *in vitro* (Fig. S15b and S15c). These findings suggest that GRXS17 may serve as a transnitrosylation mediator, transferring NO to HDA19. This is supported by yeast two-hybrid assays and computer modelling showing specific interactions between the 3 glutaredoxin domains of GRXS17 and the catalytic domain of HDA19 of which several Cys residues are S-nitrosylated (Fig. S16). Moreover, we assessed the deacetylase activity of fully complemented lines with wild type HDA19 (W) alongside partially complemented plants with mutant HDA19 carrying Cys 137 to Ala point mutations (M). The fully complemented HDA19 lines exhibit significantly elevated deacetylase activity under dew conditions (Fig. 3c), consistent with previous reports that S-nitrosylation enhances HDA19 activity (30). Although the point-mutation lines also show increased deacetylase activity following dew exposure, this enhancement is markedly reduced compared to that in the fully complemented plants. This partial increase in deacetylase activity of the point mutation lines under dew may be explained by the presence of other S-nitrosylation sites in the HDA19 protein (Fig. S17). Together, these results suggest that NO generated by extracellular micro-dewdrops can modulate histone deacetylase activity through GRXS17-mediated S-nitrosylation to control plant growth (31).

ChIP-seq profiling revealed that dew exposure enhances HDA19 binding across the genome in leaf tissues (Fig. S18 and Extended Data 1). We observed altered expression of *FT* (FLOWERING LOCUS T) under dew conditions, supporting the involvement of the NO-HDA19 pathway in flowering regulation (Fig. S20a). However, the biochemical network underlying this process appears complex. Integrated epigenomic analysis identified 21 direct HDA19 target sites showing both increased HDA19 occupancy and reduced promoter H3K14ac levels under dew conditions (Fig. S19 and Extended Data 2). These loci are involved in signaling and metabolic pathways activated by NO, which accumulates in response to dew. Co-expression network analysis further identified six gene modules enriched for signaling and metabolic processes that correlated with both NO accumulation and *FT* expression. Convergent enrichment analysis revealed three key GO terms central to the dew-NO-HDA19-FT axis (Fig. S20b and S21). Transcriptome profiling revealed 29 dew-inhibited genes with significant lower expression in the fully complemented lines relative to point-mutation lines (Fig. S22a and S22b). Among them, four genes exhibited increased HDA19 binding and reduced promoter H3K14ac under dew, and co-expression analysis confirmed their contribution to the key GO terms (Extended Data 3-5, Fig. 4b). These genes are involved in ABA biosynthesis and/or signal transduction (Fig. 4b, Fig. S22c and Extended Data 6),
including AT2G27150 (AAO3) and AT1G52340 (ABA2) (32). RT-qPCR and ChIP-qPCR confirmed that they are HDA19 direct targets under dew exposure (Fig 4c). For evaluating the impact of micro-dewdrops on ABA formation in leaves, we cultivated *Arabidopsis thaliana* under standard growth conditions (16 h light/8 h dark) with and without microdroplet spray treatments. As shown in Fig. 4d, ABA levels in the control plants remained relatively stable (~6 ng/g fresh weight) from 7 to 15 days post two-leaf stage. In contrast, microdroplet-treated plants exhibited a progressive decline in ABA concentration, decreasing from ~5 ng/g at day 7 to <2 ng/g by day 15. Phenotypically, these plants displayed premature bolting and flowering within one week of treatment, whereas control plants remained in the vegetative phase (Fig. 4e and Fig S23). Genetic analysis of flowering time in *hda19* and *grxs17* loss-of-function mutants is confounded by their inherent early-flowering phenotypes, which masks any dew-specific effects (28-29,31). To directly test the role of S-nitrosylation in this pathway, we employed a targeted approach using an HDA19c137a point-mutant, which specifically abrogates this redox-sensitive modification while preserving the protein's canonical function (30). In contrast to lines fully complemented with wild-type HDA19, the HDA19c137a lines showed no significant dew-induced decrease in ABA content and no corresponding alteration in flowering time (Fig S24). The decreased ABA synthesis may enhance gibberellic acid accumulation and signaling leading to premature flowering. Alternatively, HDA19 may repress other negative regulators of flowering. Regardless, the results provide compelling evidence that the extracellular chemical processes that occurred in micro-dewdrops on leaves can influence intracellular biochemical processes and the flowering timing of *Arabidopsis thaliana*. It is important to emphasize that dewdrop-mediated NO generation occurs after leaf unfolding, thereby influencing plant development at a later stage. This contrasts with earlier studies focusing on endogenous NO, which examined its role throughout the entire plant life cycle, including processes such as root development and flowering initiation (33). Furthermore, plant flowering is regulated by a complex network of biochemical reactions. Previous studies have shown that mechanical signals mediated by processes such as rainfall can promote flowering by activating the JA/MYC2 signaling pathway (34-35). We hypothesize that after rainfall, the microdroplets remaining on the leaf surface may also trigger chemical processes similar to those occurring in micro-dewdrops, thereby influencing the flowering process in plants. However, considering that raindrops may contain more compounds compared to dew droplets, the corresponding redox reactions are likely to be more complex and require further investigation.

**Global Dew Point Impact on Flowering.** As a globally distributed family of broad-leaved angiosperms, Brassicaceae predominantly inhabit temperate regions, where dew condensation frequently occurs on leaf surfaces. To broaden our investigation beyond species-specific boundaries and better understand the potential impact of *in vitro* physicochemical processes occurring within micro-dewdrops, we extended our analysis to the whole Brassicaceae family. We compiled flowering records for 478 species spanning 81 genera, comprising 138,580 georeferenced human observations from the Global Biodiversity Information
Facility (GBIF) database, recorded between 1990 and 2023. In total, these records represent 12,692,736 independent flowering events. The global distribution of these events is illustrated in Fig. 5a.

To assess the influence of environmental factors on flowering, we assembled a meteorological dataset derived from 670 weather stations located closest to the respective flowering observation sites. This dataset spans the same 34-year period and includes 11 daily meteorological variables: temperature, dew point temperature, mean sea level pressure, station pressure, wind speed, atmospheric visibility, maximum temperature, minimum temperature, precipitation, and relative humidity. We employed generalized linear mixed-effect models (GLMMs) to evaluate the probabilistic contribution of these variables to flowering dynamics (34), using flowering counts as the response variable (Fig. S25) and meteorological factors as predictors (Fig. S26). Since photoperiod is a biological construct not directly captured by meteorological measurements, we statistically controlled for its effect by incorporating geographic coordinates (latitude, longitude) and the date of observation (year, day-of-year) as foundational covariates in all models. The effects of proximate meteorological variables (e.g., dew point depression, visibility) and their interactions with the spatiotemporal baseline are then systematically evaluated through model comparisons (Fig. S27-30, Extended Data 7 to 8). Additionally, we hypothesize that under light conditions, the concentration of ROS in micro-dewdrops on leaf surfaces and the related redox reactions may undergo changes, potentially creating a coupling effect between dew and photoperiod on the flowering process of plants. This possible foliar chemical process warrants further investigation.

As shown in Fig. 5b and Extended Data 7-8, dew point temperature emerged as the most significant positive predictor of flowering frequency across the Brassicaceae family (contribution = 0.118, *p* = 1.18 × 10⁻⁷). The interaction between dew point temperature and visibility also had a positive effect (*p* = 0.011), suggesting that sunlight acting on dewdrops may contribute to foliar redox cascades involved in the regulation of flowering. In contrast, several variables showed significant negative associations with flowering frequency, including precipitation (contribution = -0.029, *p* = 2.90 × 10⁻⁴), mean sea level pressure (contribution = -0.015, *p* = 1.55 × 10⁻¹⁰), and atmospheric visibility alone (contribution = -0.008, *p* = 8.94 × 10⁻⁴). These findings support the hypothesis that dew formation may act as a global-scale promoter of flowering in the Brassicaceae family. We suspect that these findings can be generalized to other plant types, but this remains to be established. Importantly, this effect does not negate the well-established roles of photoperiod and temperature in floral regulation. Instead, we propose that leaf-surface micro-dewdrops serve as a supplementary modulator of flowering timing. In the context of global climate change, these results underscore the importance of considering fluctuations in nonrainfall water inputs, such as dew, in shaping plant phenology and reproductive strategies. Moreover, given the foundational role of plants as primary producers, shifts in atmospheric hydrology may have far-reaching implications for ecosystem dynamics and the geographic boundaries of environmentally sensitive zones.
257 **Conclusions**

258 Our findings uncover a previously unrecognized role for micro-dewdrops on plant surfaces as transient
259 yet potent biochemical microreactors that can trigger systemic developmental transitions. In *Arabidopsis*,
260 we show that dew condensation initiates redox cascades involving reactive oxygen species (ROS) and
261 nitric oxide (NO), modulating intracellular signaling, altering gene expression, and accelerating flowering.
262 This condensation-driven mechanism operates alongside classical photoperiodic and thermal cues,
263 adding a new dimension to our understanding of how plants integrate environmental signals. While
264 demonstrated here in *Arabidopsis*, this mechanism may represent a more general strategy by which
265 plants sense and respond to atmospheric moisture. As climate change alters atmospheric moisture
266 dynamics, our results suggest that microdroplet chemistry may influence plant developmental timing at
267 ecosystem scales, with broad implications for biodiversity, agriculture, and biosphere-atmosphere
268 interactions. These findings redefine the ecological significance of water-plant interfaces and highlight
269 how microscale physicochemical processes can shape macroscopic biological outcomes.

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271 **Materials and Methods**

272 **Plant materials and treatments.** Arabidopsis thaliana wild-type (Col-0), hda19 and grxs17 mutants, and
273 complementation lines (HDA19-HA, HDA19C137A-HA, GRXS17-MYC) were grown on 1/2 MS medium
274 for 7 days. Dew treatment was performed at 28 °C / 90 % RH for 24 h (control: 22 °C / 65 % RH).

275 **Molecular assays.** Protoplast isolation and transfection followed established standard protocols. NO
276 content was measured using DAF-FM DA fluorescence and Griess reagent. NOS activity was determined
277 via citrulline production. Protein extraction used non-reducing buffers for S-nitrosylation preservation.

278 **Protein analyses.** Co-IP was performed with anti-HA/anti-MYC antibodies. S-nitrosylation was detected
279 by TMT switch assay. HDAC activity was measured spectrophotometrically. FRET probes (Clover-
280 mRuby2 for GRXS17, CFP-Venus for HDA19) monitored SNO transfer kinetics.

281 **Omics analyses.** RNA-seq and ChIP-seq (anti-H3K14ac/anti-HA) libraries were prepared following
282 Illumina protocols and sequenced on HiSeq 2000. Data were processed using FastQC, Bowtie2, MACS2,
283 and DESeq2. WGCNA identified co-expression modules (β=25, R²>0.85).

284 **Structural studies.** Homology modeling (MODELLER) and protein docking (ZDOCK/PyROSETTA)
285 predicted GRXS17-HDA19 interactions, validated by BiFC and Y2H assays.

286 **Statistical information.** Each test was performed with at least three independent biological replicates,
287 ensuring robustness against biological variability. Data normality and homogeneity of variance were
288 confirmed using Shapiro-Wilk (p > 0.05) and Levene's tests (p > 0.05), respectively. Only when One-way
289 ANOVA indicated a significant overall effect (p < 0.05), Fisher's Least Significant Difference (LSD) test
290 was applied for post hoc pairwise comparisons. Groups with mean differences ≥ LSD were considered
291 statistically significant (p < 0.05). Analyses used R and SPSS, with data reported as mean ± SD.

292 **Additional information.** The original data of WB and the raw data of variables for GLMM analysis in this
293 study are publicly available in Extended data 9 and Extended data 10, respectively. The method details,
294 supporting figures and all extended data sets are presented in the supporting information including:

295 Extended methods
296 Methods references (1 to 6)

297 Figs. S1 to S31

298 Extended Data 1 to 10

299

300 Acknowledgements

301 We thank J. Ge and Z. Li for taking care of the plants during the experiment. This work is supported in
302 part by the National Nature Science Foundation of China (22193051, 42025704, 22125606, 22425606),
303 the Hubei Provincial Department of Education Scientific Research Project (Q20234408), the French
304 Agence Nationale de la Recherche (ANR-19-CE12-0027-01), and Stanford Sustainability Accelerator at
305 the Stanford Doerr School of Sustainability

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382
383 Figures and Tables

384
A

2021 Flowering Timeline of *Arabidopsis* (Utrecht, Netherlands)

<figure><img src="image_2.png" /></figure>

2022 Flowering Timeline of *Arabidopsis* (Utrecht, Netherlands)

<figure><img src="image_3.png" /></figure>

B

Interval between dew and flowering events

<figure><img src="image_4.png" /></figure>

386

**Figure 1** | Foliar dew modulates flowering phenology in *Arabidopsis thaliana*. **a.** Weekly timelines of dew occurrence (blue bars) and flowering periods (orange bars) in *Arabidopsis thaliana* during the 2021 and 2022 growing seasons in Utrecht, Netherlands. **b.** Distribution of intervals between dew events and subsequent flowering initiation, based on 20 years of nationwide phenological records (2004-2023). The flower occurrences were obtained from the GBIF database (Extended data 10)

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<figure><img src="image_5.png" /></figure>

**Figure 2** | Reactive species generated in foliar micro-dewdrops. **a.** A schematic diagram of a micro-dewdrop on Trichomes. **b.** A typical optical image of a micro-dewdrop on Trichomes. **c.** The corresponding fluorescence microscopy image of the micro-dewdrop contains 1 mM ROS-sensitive probe as shown in **b**. The excitation source is a green laser pointer (530 nm). **d.** Microscopy images of *Arabidopsis* leaves without and with a micro-dewdrop contains 1 mM NO-sensitive probe under the excitation laser of 495 nm. **e.** Quantification of absolute NO content (nmol/mg protein) in Arabidopsis with and without dew. Data are presented as mean ± SD (n = 5 biological replicates from 2-week-old leaves) indicated by circle (without dew) and triangle (with dew). Different letters indicate significant differences (p < 0.05). NO content was determined using the Griess reagent and quantified against a sodium nitrite standard curve. **f.** Quantification of absolute NOS activity (nmol/min/mg protein) in *Arabidopsis* with and without dew. Data are presented as mean ± SD (n = 5 biological replicates from 2-week-old leaves) indicated by circle (without dew) and triangle (with dew). Different letters indicate significant differences (p < 0.05). NOS activity was assayed by measuring citrulline production
411 fluorescence and quantified against a citrulline standard curve. All measurements were

412 performed with three technical replicates. The scale bars are 100 µm for both panel c and d.

413
<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /></figure>

<figure><img src="image_8.png" /></figure>

<figure><img src="image_9.png" /><figcaption>**Figure 3** | Dew exposure enhances nuclear GRXS17-HDA19 interaction and deacetylase activity of HDA19 isolated from nucleus. **a.** Confocal microscopy of *Arabidopsis* leaf cells (isolated from 3 independent 2-week-old seedlings) showing nuclear accumulation of NO (green, DAF-FM) and GRXS17-HDA19 interaction (yellow, YFP signal). **b.** Immunoblot analysis of S-nitrosylated (SNO) HDA19 and GRXS17 in *Arabidopsis* leaves with and without dew. Data are normalized to the control (without dew) and presented as mean ± SD (n = 3). **c.** Quantification of deacetylase activity of nuclear HDA19 in leaves with and without dew exposure. Data are means ± SD (n = 5). Different letters denote statistically significant differences (p < 0.05). The scale bar in panel **a** is 5 µm.</figcaption></figure>

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a

<figure><img src="image_10.png" /></figure>

c

<figure><img src="image_11.png" /></figure>

b

<figure><img src="image_12.png" /></figure>

ABA2

Reductase involved in ABA biosynthesis (AT1G52340)

<figure><img src="image_13.png" /></figure>

d

<figure><img src="image_14.png" /></figure>

e

<figure><img src="image_15.png" /></figure>

427

**Figure 4** | Dewdrop-induced epigenetic silencing of ABA synthesis accelerates flowering in *Arabidopsis*. **a.** A schematic model illustrating how dewdrops promote the S-nitrosylation of HDA19, enhancing its histone deacetylase activity and repressing gene expression by reducing histone H3K14 acetylation. **b.** Venn diagram showing the overlap between dewdrop-

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431
downregulated floral hub genes with reduced H3K14ac levels and HDA19 binding loci (left), Gene Significance (GS) quantifying the correlation of hub genes with flowering (right), two GO terms showing enriched functional bio-processes of the four HDA19-targeted floral hub genes. c. HDA19-mediated repression of ABA biosynthesis genes. Dewdrop exposure reduces transcription levels (RT-qPCR) and H3K14ac acetylation (ChIP-qPCR) while increasing HDA19 binding (ChIP-seq) at the promoters of *AAO3* and *ABA2*. This demonstrates dewdrop-induced epigenetic repression of ABA biosynthesis genes via HDA19-mediated histone deacetylation. IgG were used as a negative control. Data are presented as mean ± SD of three biological replicates indicated by circle (with dew) and triangle (without dew). Different lowercase letters (a, b, c) above bars indicate statistically significant differences between groups (one-way ANOVA with Tukey's HSD test, p < 0.05). Primers used in this study are shown in **Extended Data S5. d. Quantification of ABA levels in developing leaves from 7 to 15 days after two-leaf stage in plants with and without microdroplet spray exposure. e. Phenotypic analysis of Arabidopsis plants grown under control conditions (top) or exposed to microdroplet spray (bottom).**
448

FIGURE 5

a

<figure><img src="image_16.png" /></figure>

b

<figure><img src="image_17.png" /></figure>

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451

**Figure 5** | Global patterns and environmental cues of Brassicaceae flowering. **a.** Global distribution of Brassicaceae flowering counts from 1990 to 2023. **b.** Probabilistic assessment of environmental factors influencing Brassicaceae flowering. A contribution model quantifies the directional effects of key environmental signals on flowering events.

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a. 2021 Flowering Timeline of *Arabidopsis* (Utrecht, Netherlands)

<figure><img src="image_18.png" /></figure>

2022 Flowering Timeline of *Arabidopsis* (Utrecht, Netherlands)

<figure><img src="image_19.png" /></figure>

b. Interval between dew and flowering events

<figure><img src="image_20.png" /></figure>
<figure><img src="image_21.png" /></figure>

<figure><img src="image_22.png" /></figure>

<figure><img src="image_23.png" /><figcaption>d NO in micro-dewdrop</figcaption></figure>

<figure><img src="image_24.png" /><figcaption>e Relative NO content (%)</figcaption></figure>

<figure><img src="image_25.png" /></figure>

<figure><img src="image_26.png" /><figcaption>f Relative activity (%)</figcaption></figure>

<figure><img src="image_27.png" /></figure>
(DAF-FM)

(DAPI)

GRXS17 signal
(YFP)

Merge

With dew

<figure><img src="image_28.png" /></figure>

<figure><img src="image_29.png" /></figure>

<figure><img src="image_30.png" /></figure>

<figure><img src="image_31.png" /></figure>

Without dew

<figure><img src="image_32.png" /></figure>

<figure><img src="image_33.png" /></figure>

<figure><img src="image_34.png" /></figure>

<figure><img src="image_35.png" /></figure>

b

<figure><img src="image_36.png" /></figure>

<figure><img src="image_37.png" /></figure>

c

<figure><img src="image_38.png" /></figure>
<caption>a</caption>

Leaves
without dewdrops

<figure><img src="image_39.png" /></figure>

Leaves
with dewdrops

<figure><img src="image_40.png" /><figcaption>c</figcaption></figure>

### AAO3
Abscisic aldehyde oxidase (AT2G27150)

<figure><img src="image_41.png" /><figcaption>b</figcaption></figure>

Significant up HDA19
binding locus caused decreased H3K14ac by dew

The correlation of hub genes with flowering

<figure><img src="image_42.png" /></figure>

**AT2G27150**
A aldehyde oxidase catalyzing the final step in ABA biosynthesis
0.95

**AT1G62340**
A cytosolic reductase involved in ABA biosynthesis
0.92

**AT2G48030**
DNAse I-like superfamily protein
0.85

**AT2G01540**
Related to GTPase activity
0.88

Abscisic acid biosynthetic process GO:0009688

Regulation of signal transduction GO:0009966

### ABA2
Reductase involved in ABA biosynthesis (AT1G52340)

<figure><img src="image_43.png" /><figcaption>d</figcaption></figure>

<figure><img src="image_44.png" /></figure>

The growth time after 2-leaf stage (Days)

<caption>e</caption>

Culture in perti dish

<figure><img src="image_45.png" /></figure>

7-day-old leaves after 2-leaf stage

<figure><img src="image_46.png" /></figure>

15-day-old leaves after 2-leaf stage

Culture in perti dish under
microdroplets spray exposure

<figure><img src="image_47.png" /></figure>

<figure><img src="image_48.png" /></figure>
a

<figure><img src="image_49.png" /><figcaption>Global pattern of Brassicaceae flowering recorded from 1990 - 2023</figcaption></figure>

b

<figure><img src="image_50.png" /><figcaption>Probabilistic contribution of environmental signal to flower</figcaption></figure>