Paul E. Verslues and Toshisangba Longkumer, Institute of Plant and Microbial Biology, Academia Sinica, Taipei, TAIWAN
Background: Plants can deliberately slow down their growth in response to even a small decrease in water availability. This can help plants prepare for further drying, but can also be a disadvantage in agriculture. Understanding how growth is regulated during drought is required to generate plants that maintain more growth during short term or moderate severity drought stress. We previously found that Arabidopsis Clade E Growth-Regulating (EGR) phosphatases restrain growth during stress. EGRs do this in part by affecting the function of Microtubule-Associated Stress Protein 1 (MASP1). MASP1 can promote growth during drought stress.
Question: We wanted to know whether EGRs and MASP1 affect root growth primarily by controlling how many cells are produced by cell division in the root meristem or by controlling how big cells become after they stop dividing (or both). We also wanted to better understand where in the plant EGRs and MASP1 are expressed and why they have opposing effects on growth.
Findings: Ectopic EGR expression suppressed growth during water stress and reduced the number of dividing cells in the Arabidopsis root meristem. Conversely, ectopic MASP1 expression enhanced growth maintenance during stress and increased root meristem size. EGR2 was expressed in cortex cells at the distal end of the meristem of unstressed plants but encroached closer to the root tip during stress. MASP1 was expressed in the dividing cells of the root meristem. When a phosphomimic version of MASP1 was expressed, EGR was no longer able to suppress root meristem size. Thus, EGR dephosphorylation of MASP1 in their overlapping zone of expression suppresses root meristem size, and growth, during drought stress.
Next steps: We are identifying additional targets of EGR regulation important for growth maintenance during stress. We are also identifying MASP1-interacting proteins and additional MASP1 phosphorylation sites to understand how MASP1 promotes cell division.
Toshisangba Longkumer, Chih-Yun Chen, Marco Biancucci, Govinal Badiger Bhaskara, Paul E. Verslues. (2022). Spatial differences in stoichiometry of EGR phosphatase and Microtubule-Associated Stress Protein 1 control root meristem activity during drought stress. https://doi.org/10.1093/plcell/koab290