# Yield maintenance under drought: expansive growth and hydraulics also matter in reproductive organs

Olivier Turc, Vincent Oury, Yves Gibon, Duyên Prodhomme, Francois Tardieu

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Olivier Turc, Vincent Oury, Yves Gibon, Duyên Prodhomme, Francois Tardieu. Yield maintenance under drought: expansive growth and hydraulics also matter in reproductive organs. Interdrought V, Feb 2017, Hyderabad, India. 2017. hal-01605905

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# IDT6-055 | Yield maintenance under drought: expansive growth and hydraulics also matter in reproductive organs

Turc O<fnref n="1" />*, Oury V<fnref n="1" />, Gibon Y<fnref n="2" />, Prodhomme D<fnref n="2" />, Tardieu F<fnref n="1" />

Yield maintenance under drought in maize (Zea mays) is associated with flowering synchrony which requires the rapid extension of styles and stigma (silks) to be accessible for pollen. We have shown that the control of grain set under moderate water deficits similar to those in the field result from a developmental process linked to the timing of silk growth, in opposition to the common view that abortion is linked to the sugar metabolism in ovaries. A switch to abortion occurs 2-3 days after first silk emergence in water-stressed plants, when silk growth stops simultaneously for all ovary cohorts, and explains abortion rates in different treatments, genotypes and positions on the ear. Analyses of transcripts and metabolites indicate that the first molecular events occur in silks rather than in ovaries, and involve genes

affecting expansive growth rather than sugar metabolism. Sugar availability is preserved in ovaries until the switch to abortion, and the disruption of carbon metabolism only occurs afterwards. Hence, changes in metabolite contents, transcript amounts and enzyme activities involved in ovary sugar metabolism would be a consequence rather than a cause of the beginning of ovary abortion. Patterns of silk growth responses to environment share common features with those of leaf growth, with both kinetic and genetic evidences. These findings have large consequences for breeding drought tolerant maize and for modelling grain yields under drought. Oury et al (2016) *Plant Physiology* 171: 986-996 and 171: 997-1008

Turc et al (2016) *New Phytologist* 212: 377-388

# IDT6-056 | An aromatic twist in the quest of biofortification

Vanishri B R<fnref n="1" />, Holla S K M<fnref n="1" />, Sowjanya M S<fnref n="1" />, Avinash M<fnref n="1" />, Kakade S<fnref n="1" />, Shashidhar H E<fnref n="1" />*

Aerobic rice has been an effective strategy to combat drought. However, this technology was not focusing on quality parameters such as micronutrients. Zinc deficiency causes hidden hunger and is the usual target for biofortification. Aroma in rice plays a significant role in enhancing the market value and consumer's preference. Zinc and aroma are highly valued grain quality traits. In the quest of enhancing micronutrients, getting a biofortified, aromatic, aerobic rice variety would be an added advantage. Considering all these factors, a study was conducted to dissect the relationship between micronutrients and aroma under aerobic condition using 14 aerobic rice genotypes. All these elite accessions were screened for zinc content and aroma along with yield parameters. Genotypes exhibited significant variation for all traits studied. Sensory evaluation of aroma showed that nine

genotypes were scented and five were non-scented. Azucena, an aromatic variety, had highest zinc content before and after polishing. Among all the tested genotypes *Chittimutyalu* was strongly scented and showed very less loss of Zn after polishing. The top four genotypes for brown rice zinc concentration, which are above the international target, were aromatic lines. AM65, a rice accession in the pipeline as a micronutrient-rich aerobic accession, was highly aromatic. Molecular marker analysis was done by using markers designed specific to gene *LPAAT*. All seven designed markers were monomorphic. Sequencing of the amplicons indicated nucleotide variations in six markers which were associated to aroma and zinc. Our results indicate that there is positive relationship between low moisture, Zn content and grain aroma.

<footnote n="1">¹ INRA LEPSE, Montpellier, F-34000, France;</footnote>

<footnote n="2">² INRA Biologie du Fruit et Pathologie, Villenave d'Ornon, F-33882, France;</footnote>

<footnote>*E-mail: olivier.turc@supagro.inra.fr</footnote>

<footnote n="1">¹Department of Plant Biotechnology, UAS, GVKV, Bangalore 560065, Karnataka, India</footnote>

<footnote>*E-mail: heshashidhar@uasbangalore.edu.in</footnote>
# Yield maintenance under drought: expansive growth and hydraulics also matter in reproductive organs

Olivier TURC¹, Vincent OURY¹, Yves GIBON², Duyên PRODHOMME² and François TARDIEU¹

¹UMR 759 Laboratoire d'Ecophysiologie des Plantes sous Stress Environnementaux (LEPSE), INRA Montpellier, France

²UMR 1332 Biologie du Fruit et Pathologie (BFP), INRA Bordeaux, France

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## 1 Summary

Yield maintenance under drought in maize (Zea mays) is associated with flowering synchrony which requires the rapid extension of styles and stigma (silks) to be accessible for pollen. We show here that the control of grain set under moderate water deficits similar to those in the field results from a developmental process linked to the timing of silk growth, itself related to expansive growth and hydraulics processes, in opposition to the common view that abortion is linked to the sugar metabolism in ovaries.

## 3 A switch to abortion occurs rapidly after first silk emergence.

Silk elongation rate decreased in water deficit and stopped 2-3d after first silk emergence, simultaneously for all ovary cohorts, vs 7-8d in well-watered plants. Abortion rate in different hybrids, treatments and positions on the ear (Fig. 3) was accounted for by the superposition of the sequential emergence of silks originating from ovaries of different cohorts along the ear with the simultaneous silk growth arrest. Abortion occurred in the youngest ovaries whose silks did not emerge 2d before silk arrest (Fig. 4). This mechanism accounted for more than 90% of drought-related abortion in our experiments (Fig. 5).

<figure><img src="image_5.png" /><figcaption>Fig. 3</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>Fig. 4</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>Fig. 5</figcaption></figure>

## 2 Perform realistic water deficits and abortion rates in controlled platforms

Four maize hybrids were grown in pots and subjected to different levels of soil water availability in greenhouse and growth chamber experiments (*Phenodyn* phenotyping platform). Soil water status was managed by weighing pots and adjusting water supply to the target soil water content. Three treatments were applied from tassel emergence (TE) to 7d after first silk emergence (SE), namely well watered (WW), mild deficit (WD1) and moderate deficit (WD2), with soil water potential above -0.10 MPa, around -0.25 MPa and around -0.50 MPa respectively (Fig. 1A). Their impacts on photosynthesis (Fig. 1C), transpiration (Fig. 1B) and seed set (Fig. 2) were similar to those commonly observed in drought prone fields.

<figure><img src="image_8.png" /><figcaption>Fig. 1</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>Fig. 2</figcaption></figure>

## 4 Silk growth is controlled by xylem water potential

Analyses of transcripts and metabolites indicate that the first molecular events induced by drought occur at first silk emergence (SE), in silks rather than in ovaries, and involve genes affecting expansive growth rather than sugar metabolism (Fig. 6). Silk elongation rate was measured using displacement transducers (Fig. 7). Time courses revealed that silk elongation rate closely followed changes in soil water status and evaporative demand, with day-night alternations similar to those in leaves (Fig. 8, Fig. 9). Day-night alternations were steeper with high than low plant transpiration rate, manipulated via evaporative demand or by covering part of leaf area (Fig. 9). Half times of changes in silk elongation rate upon changes in evaporative demand or soil water status were of 10-30 minutes (Fig. 8), similar to those in leaves, suggesting a common hydraulic control of expansive growth in both vegetative and reproductive structures.

<figure><img src="image_10.png" /><figcaption>Fig. 8</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>Fig. 6</figcaption></figure>

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<figure><img src="image_13.png" /><figcaption>Fig. 9</figcaption></figure>

## 5 Carbon metabolism in ovaries was still unaffected at silk emergence

Changes in concentration and amount of sugars (Fig. 10), in activities of enzymes (Fig. 10) and in transcript levels (Fig. 11) of genes of sugar metabolism occurred 5 d after silk emergence in apical ovaries that eventually aborted, i.e. after the switch to abortion of these ovaries. Hence, we propose that, under moderate water deficits corresponding to most European drought scenarios, changes in ovary carbon metabolism during flowering time are a consequence rather than a cause of the beginning of ovary abortion.

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<figure><img src="image_15.png" /><figcaption>Fig. 10</figcaption></figure>

<figure><img src="image_16.png" /><figcaption>Fig. 11</figcaption></figure>

<figure><img src="image_17.png" /><figcaption>Fig. 13</figcaption></figure>

<figure><img src="image_18.png" /><figcaption>Fig. 12</figcaption></figure>

## 6 Perspectives

These results confer a pivotal role to hydraulic controls of expansive growth processes in grain yield elaboration upon changes in environmental conditions. They have large consequences in plant breeding, modelling and phenotyping. Genotypes largely differ for the sensitivity of silk elongation rate to xylem water potential (Fig. 12), and sensitivities of silk and leaf growth were correlated (Fig. 13). This opens the way for genetic studies of the traits, genes and physiological processes controlling grain set under non-optimal climatic scenarios. These sensitivities and their genetic variability have to be included in the formalisms of crop models simulating yield in maize (e.g. APSIM model). An original method for phenotyping silk growth is currently developed by our group (companion poster IDT6-014).

Oury V, Caldeira CF, Prodhomme D, Pichon J-P, Gibon Y, Tardieu F, Turc O. 2016. Is change in ovary carbon status a cause or a consequence of maize ovary abortion in water deficit during flowering? *Plant Physiology* 171: 997-1008.

Oury V, Tardieu F, Turc O. 2016. Ovary apical abortion under water deficit is caused by changes in sequential development of ovaries and in silk growth rate in maize. *Plant Physiology* 171: 986-996.

Turc O, Bouteillé M, Fuad-Hassan A, Welcker C, Tardieu F. 2016. The growth of vegetative and reproductive structures (leaves and silks) respond similarly to hydraulic cues in maize. *New Phytologist* 212: 377-388.

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