Contribution of vasculature to stem integrity in Arabidopsis thaliana

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Asaoka, Mariko | Sakamoto, Shingo | Gunji, Shizuka | Mitsuda, Nobutaka | Tsukaya, Hirokazu | Sawa, Shinichiro | Hamant, Olivier | Ferjani, Ali

Edité par CCSD ; Company of Biologists -

International audience. In plants, coordinated growth is important for mechanical integrity in organs because cells remain contiguous through their walls. So far, defects in inflorescence stem integrity in Arabidopsis thaliana have mainly been related to epidermal defects (i.e., cell-cell adhesion defects or weaker walls). Although these observations suggest a growth-limiting function at the stem cortex, deeper layers of the stem could also contribute to stem integrity. The nac secondary cell wall thickening promoting factor1 (nst1) nst3 double mutant background is characterized by weaker vascular bundles without cracks. By screening for the cracking phenotype in this background, we identified a novel regulator of stem cracking, the transcription factor INDETERMINATE DOMAIN9 (IDD9). Stem cracking was not caused by vascular bundle breakage in plants that expressed a dominant repressor version of IDD9. Instead, cracking emerged from increased cell expansion in non-lignified interfascicular fiber cells that stretched the epidermis. This phenotype could be enhanced through clavata3-dependent cell proliferation. Collectively, our results demonstrate that stem integrity relies on three additive mechanical components: the epidermis that resists inner cell growth, cell proliferation in inner tissues, and growth heterogeneity associated with vascular bundle distribution in deep tissues.

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