LAUSR

Shoot apical meristem (SAM) and root apical meristem (RAM) act as pools of stem cells to give rise to aboveground and underground tissues and organs in higher plants. Despite the structure differences between these two meristems, they evolve similar signaling pathways to maintain stem cell homeostasis. The CLAVATA3 (CLV3)-WUSCHEL (WUS) negative feedback loop acts as a core pathway in controlling SAM homeostasis, while CLV3/EMBRYO SURROUNDING REGION (ESR) 40 (CLE40) and WUSCHEL-RELATED HOMEOBOX5 (WOX5), homologues of CLV3 and WUS, direct columella stem cell fate. It has been shown that CLV3 INSENSITIVE KINASES (CIKs) are essential for maintaining SAM homeostasis. Whether CIKs regulate the distal root meristem remains to be elucidated. Here, we report that CIKs are indispensable for transducing the CLE40 signal to maintain homeostasis of the distal root meristem. The cik mutants displayed disrupted quiescent center and delayed columella stem cell (CSC) differentiation. Biochemical assays demonstrated that CIKs interact with ARABIDOPSIS CRINKLY4 (ACR4) in a ligand-independent manner and can be phosphorylated by ACR4 in vitro. In addition, the phosphorylation level of CIKs can be rapidly induced by CLE40, which partially depends on ACR4. Though CIKs act as conserved and redundant regulators in the SAM and RAM, our results demonstrated that they exhibit differentiated functions in these meristems.