# Do Arabidopsis inflorescences twist in Space?

Nathalie Leblanc-Fournier, Mélanie Decourteix, Jérôme Franchel, Félix Hartmann, Khan Kinza, Nicole Brunel-Michac, Bruno Moulia, Valérie Legué

► To cite this version:

Nathalie Leblanc-Fournier, Mélanie Decourteix, Jérôme Franchel, Félix Hartmann, Khan Kinza, et al.. Do Arabidopsis inflorescences twist in Space?. 28th-European Low gravity research Association-Biennial Symposium & general Assembly, ELGRA, Sep 2024, Liverpool, United Kingdom. hal-04876932

HAL Id: hal-04876932

https://hal.science/hal-04876932v1

Submitted on 9 Jan 2025

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UNIVERSITÉ
Clermont Auvergne

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# DO ARABIDOPSIS INFLORESCENCES TWIST IN SPACE?

Leblanc-Fournier N¹, Decourteix M, Franchel J, Hartmann F, Khan K, Brunel-Michac N, Moulia B, Legué V¹

Université Clermont Auvergne, INRAE, PIAF, 63000 Clermont-Ferrand, France. ¹Nathalie.leblanc@uca.fr and valerie.legue@uca.fr

On Earth, plants are able to stand upright by continuously adjusting their posture in response to various environmental signals such as light and gravity.

However, quantification of the spatio-temporal variations of the curvature of the organs, during phototropic or gravitropic recovery, enlightened that successive phases of curvature and de-curvature cannot be explained by the sole perception of the inclination of the plant or of light direction: the **plants also perceive their own curvature**.

* **Proprioception** was thus defined as the ability of a plant organ to sense its local curvature.

* This sensing drives the progressive establishment of organ straightening (1-4). Combined with gravisensing and light perception, proprioception regulates the dynamics of growth of the aerial organs.

The specific molecular mechanisms governing this process remain elusive: a quantitative approach is needed to compare different mutants and to decorrelate proprioception from gravisensing.

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## A generic phenotyping tool to analyse postural control and proprioception on earth:

The cycle of tropic responses after sensing of the direction of gravity g and direction of light l (with A the angle between l and the vertical).

### ✓ Tilt-Bend-Then-Clinostat experiments with time-lapse imaging

Plants are initially tilted horizontally in dark during 60 min to trigger the typical gravitropic upward curvature of the inflorescence stem.

Horizontal continuous rotation (clinostat) is applied during 600 min to disrupt statolith-driven graviperception.

As expected, after 300 min, WT plants rely on curvature sensing to adjust their growth and tend to rectify the organ by decreasing its curvature. In RNAi-vln2vln3 transgenic lines, where the expression of *VLN2* and *VLN3* genes encoding actin-bundling proteins are reduced in fibres, the inflorescence stem is still curved after 300 min suggesting a role of the actin network in the proprioceptive response.

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Treatments applied to decorrelate gravity sensing from proprioception (A) and overlay of pictures illustrating typical stem shapes acquired by WT and transgenic plants along the experiment (B).

Pictures are taken every 6 min. T corresponds to minutes.

### ✓ Quantitative analyses of gravi- and proprioceptive sensitivities with mathematical model-assisted approach

#### The mathematical model ACE (5):

The rate of change of curvature (dC/dt) in stem segment S is directly proportional to the sensitivity ($\tilde{\beta}$) to the inclination angle (A) and sensitivity ($\tilde{\gamma}$) to its own curvature C (s,t) in space (s) and time (t):

$$ \frac{dC(s,t)R}{dt} = \underbrace{\dot{E}(s,t)}_{\text{growth}} \left( -\underbrace{\tilde{\beta}A(s,t)}_{\text{gravi}} - \underbrace{\tilde{\gamma}C(s,t)R}_{\text{proprio}} \right) \quad \text{The Relative elongation rate } \dot{E} \text{ is:} $$

The stem radius (R) and the length of the growing zone (Lgz) are measured through image analysis with Interekt software. Gravi- ($\tilde{\beta}$) and proprioceptive ($\tilde{\gamma}$) parameters, are deduced graphically studying curvature variation at specific times: when C (s,t) is very low (at the beginning of gravitropic response) or when gravity is not perceived (clinostat on) (6).

Such phenotypic approach allowed us to identify non-proprioceptive plants. Here, RNAi-vln2vln3 plants have a lower $\tilde{\gamma}$ value than WT for two independent transgenic lines whereas no differences were detected for $\tilde{\beta}$ parameter. These results confirmed the role of actin network in proprioception in Arabidopsis.

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**Interekt: a software devoted to the analysis of growth monitoring experiments.**

After organ shape detection, the analysis allows both the geometric description of organs (radius, length, angles, curvatures) and the kinematics analysis (growth rate, changes in angle and curvature). Gravi- and proprioceptive parameters ($\tilde{\beta}$, $\tilde{\gamma}$) are deduced following ACE model after phenotyping 20 plants of each genotype.

#### Plant Posture in space: a space experiment that aims to decipher the impact of multiple stresses induced by spaceflight conditions on proprioceptive sensitivity:

Actin cytoskeleton has often been reported as a significant component of models explaining gravitropism (7). But the apparent promotion of the gravitropic response observed after disruption of the F-actin network could result from an impaired proprioception and straightening response.

Applying our model-assisted phenotyping approach on plants grown on the International Space Station (ISS) will offer the unique opportunity to investigate the proprioception process in microgravity and under spaceflight induced-stresses.

Stem curvature of wild-type plants and targeted mutants will be induced through directional blue light treatment in the Advanced Plant Habitat (APH) growth facility developed by NASA (8).

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**Spaceflight experimental workflow:** After a period of growth during which the lighting will come from the top, a phototropic curvature of the inflorescence stems will be generated by a unilateral blue lighting. During the phase of straightening, the plants will be maintained in dark conditions. Time-lapse imaging will be performed during the two last steps. At key time points during the experiment, the plants will be harvested for transcriptomic analysis on ground.

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**The Advanced Plant Habitat (APH) facility** is equipped with several cameras that are useful for the monitoring of growth and orientation of Arabidopsis inflorescence stems. A blue light device will be developed by CNES to induce and monitor phototropic curvature.

<footnote>(1) Moulia B., Bastien R., Chauvet-Thiry H., Leblanc-Fournier N., 2019. Posture control in land plants: growth, position sensing, proprioception, balance, and elasticity. Journal of Experimental Botany 70 (14).</footnote>

<footnote>(2) Bastien R., Douady S., Moulia B. (2015). A Unified Model of Shoot Tropism in Plants: Photo-, Gravi- and Propio-ception. Plos Computational Biology 11, e1004037.</footnote>

<footnote>(3) Moulia B., Douady S., Hamant O. (2021) Fluctuations shape plants through proprioception. Science. 372(6540):eabc6868.</footnote>

<footnote>(4) Moulia B., Badel E., Bastien R., Duchemin L. and Eloy C. (2022), The shaping of plant axes and crowns through tropisms and elasticity: an example of morphogenetic plasticity beyond the shoot apical meristem. New Phytol, 233: 2354-2379.</footnote>

<footnote>(5) Bastien R., Bohr T., Moulia B., Douady S. (2014) A unifying modeling of plant shoot gravitropism with an explicit account of the effects of gravity. *Frontiers in Plant Science*, 5, 136</footnote>

<footnote>(6) Hartmann FP, Chauvet-Thiry H et al, 2022. Methods for a Quantitative Comparison of Gravitropism and Posture Control Over a Wide Range of Herbaceous and Woody Species. In: Blancaflor EB (eds) Plant Gravitropism. Methods in Molecular Biology</footnote>

<footnote>(7) Morita MT. (2010) Directional Gravity Sensing in Gravitropism. Annu. Rev. Plant Biol. 60: 705-20</footnote>

<footnote>(8) Monje O, Richards JT, Carver JA, Dimapilis DI, Levine HG, Dufour NF and Onate BG (2020) Hardware Validation of the Advanced Plant Habitat on ISS: Canopy Photosynthesis in Reduced Gravity. *Front. Plant Sci.* 11:673. doi: 10.3389/fpls.2020.00673</footnote>