Title: The YDA-MKK4/MKK5-MPK3/MPK6 cascade functions downstream of the RGF1-RGI ligand-receptor pair in regulating mitotic activity in the root apical meristem

Yiming Shao, Xinxing Yu, Xuwen Xu, Yong Li, Wenxin Yuan, Yan Xu, Chuanzao Mao, Shuqun Zhang, Juan Xu

Abstract

The mitotic activity of root apical meristem (RAM) is critical to the primary root growth and development. Previous studies have identified ROOT GROWTH FACTOR 1 (RGF1), a peptide ligand, and its receptor RGF1 INSENSITIVE (RGI), a clade of five leucine-rich-repeat receptor-like kinases, in promoting cell division in RAM, which determines the primary root length. However, the downstream signaling components remain elusive. In this study, we identify a complete mitogen-activated protein kinase (MAPK or MPK) cascade, composed of YDA, MKK4/MKK5, and MPK3/MPK6, that functions downstream of the RGF1-RGI ligand-receptor pair. Similar to rgi1/2/3/4/5 quintuple mutant, loss of function of MPK3 and MPK6, MKK4 and MKK5, or YDA leads to a short root phenotype, which is associated with reduced mitotic activity and lower expression of PLETHORA 1 (PLT1)/PLT2 in the RAM. Furthermore, MPK3/MPK6 activation in response to exogenous RGF1 treatment is impaired in the rgi1/2/3/4/5 quintuple, yda single, and mkk4 mkk5 double mutants. Epistatic analyses demonstrated that the expression of constitutively active MKK4, MKK5, or YDA driven by the RGI2 promoter can rescue the short root phenotype of the rgi1/2/3/4/5 mutant. Taken together, these results suggest that the YDA-MKK4/MKK5-MPK3/MPK6 cascade functions downstream of the RGF1-RGI ligand-receptor pair and upstream of PLT1/PLT2 to modulate the stem cell population and primary root growth in Arabidopsis.

Link: https://doi.org/10.1016/j.molp.2020.09.004