大背景：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. 

小背景：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. 

提出问题：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. 

主要发现：Here, we report that CIKs are indispensable for transducing the CLE40 signal to maintain homeostasis of the distal root meristem.

结果1-突变体：The cik mutants displayed disrupted quiescent center and delayed columella stem cell (CSC) differentiation. 

结果2-互作蛋白：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. 

结论：Though CIKs act as conserved and redundant regulators in the SAM and RAM, our results demonstrated that they exhibit differentiated functions in these meristems.

 摘 要 

高等植物中的茎间分生组织（SAM）和根尖分生组织（RAM）作为干细胞池，分别是地上和地下组织、器官的来源。尽管两个分生组织在结构上相差较大，但是它们演化出了相似的信号转导途径，以维持干细胞内稳态。CLV3-WUS负反馈环作为控制SAM内稳态的核心途径，而CLV3同源蛋白CLE40和WUS同源蛋白WOX5决定根冠柱干细胞的命运。已有的研究显示CIKs对于维持SAM内稳态至关重要。而CIKs是否调控远端根分生组织仍有待阐明。本文中，作者报道了CIKs对于转导CLE40信号以维持远端根分生组织的稳态是必不可少的。cik突变体表现出静止中心紊乱，并且根冠柱干细胞（CSC）的分化延迟。生化试验显示CIKs会与ACR4以一种不依赖于配体的方式发生互作，并且能够在体外被ACR4磷酸化。另外，CLE40会快速诱导CIKs的磷酸化水平，并且部分依赖于ACR4。尽管，CIKs在SAM和RAM中起着保守且冗余的调节作用，但本文的研究结果表明CIKs在这些分生组织中表现出分化的功能。