Arabidopsis floral buds are locked through stress-induced sepal tip curving

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Trinh, Duy-Chi | Melogno, Isaty | Martin, Marjolaine | Trehin, Christophe | Smith, Richard, S | Hamant, Olivier

Edité par CCSD ; Nature Publishing Group -

International audience. In most plant species, sepals -the outermost floral organs -provide a protective shield for reproductive organs. How the floral bud becomes sealed is unknown. To address this question, we analyzed how the sepal grows and curves during development in Arabidopsis thaliana. We identified a local discontinuity in a small region at the tip where the sepal is markedly curved inward at a very early stage. This local hook remains curved even after anthesis. As predicted by analog and computational models, building on quantitative growth analysis, we find that this local deformation emerges from growth arrest at the tip at a stage when microtubules align with growthderived tensile stress. To test whether microtubules in that region are required to deform the sepal tip and seal the floral bud, we generated a transgenic line expressing a protein that depolymerizes microtubules specifically at the sepal tip early on, and we observed a lack of tip deformation, resulting in open floral buds. We confirmed this result in a mutant with defective growth arrest at the tip. We propose that floral buds are locked thanks to a stress-derived growth arrest event curving the sepal tip and forming a rigid hook early on during flower development.

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