To repress or to activate: that is what defines leaf shape

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By Hui Wang, College of Grassland Science and Technology, China Agricultural University, Beijing, China

 Wang and colleagues explore how two WUSCHEL-like transcription factors affect leaf blade outgrowth in Medicago truncatula and Nicotiana sylvestris

 Background: Members of the plant-specific WOX family of transcription factors are key regulators of meristem maintenance and lateral organ development. We have shown previously that STENOFOLIA (STF) from Medicago truncatula and LAMINA1 (LAM1) from Nicotiana sylvestris function as repressors, while the intermediate member WOX9 behaves as an activator. Ectopic expression of WOX9 in both stf and lam1 mutant backgrounds exacerbates their respective phenotypes, while silencing of WOX9 by RNA interference in each mutant partially rescues both the stf and lam1 mutant phenotypes, indicating that WOX9 functions antagonistically to STF/LAM1 in leaf blade development. However, the molecular mechanism of this antagonistic regulation remains unknown.

Question:  We aimed to identify the common targets of STF/LAM1 and WOX9 and their underlying mechanism during leaf blade outgrowth.

Findings :  We demonstrated the antagonistic regulation of active cytokinin contents through regulating cytokinin degradation by two evolutionarily distinct groups of WOX transcription factors: repression by LAM1/modern clade and activation by WOX9/intermediate clade. We also determined that LAM1 physically interacted with NsWOX9, and that both LAM1 and NsWOX9 directly bind to the same cis-elements of the cytokinin oxidase 3 (NsCKX3) promoter in vivo to control local cytokinin levels in balancing the cell proliferation and differentiation to regulate leaf blade expansion.

Nest steps:  As we noticed that the phenotypic rescue the stf/lam1 mutant was not complete, further experiment should focus on the identification of the additional components needed to fully rescue the stf/lam1 phenotypes.

Reference:

Hui Wang, Xue Li, Tezera Wolabu, Ziyao Wang, Ye Liu, Dimiru Tadesse, Naichong Chen, Aijiao Xu, Xiaojing Bi, Yunwei Zhang, Jianghua Chen, Million Tadege (2022). WOX family transcriptional regulators modulate cytokinin homeostasis during leaf blade development in Medicago truncatula and Nicotiana sylvestris. https://doi.org/10.1093/plcell/koac188