背景回顾-CLV3-CLV1-WUS：Stem cell homeostasis in plant shoot meristems requires tight coordination between stem cell proliferation and cell differentiation. In Arabidopsis, stem cells express the secreted dodecapeptide CLAVATA3 (CLV3), which signals through the leucine-rich repeat (LRR)-receptor kinase CLAVATA1 (CLV1) and related CLV1-family members to downregulate expression of the homeodomain transcription factor WUSCHEL (WUS). WUS protein moves from cells below the stem cell domain to the meristem tip and promotes stem cell identity, together with CLV3 expression, generating a negative feedback loop. 

提出问题：How stem cell activity in the meristem centre is coordinated with organ initiation and cell differentiation at the periphery is unknown. 

结果-CLE40-BAM1-WUS：We show here that the CLE40 gene, encoding a secreted peptide closely related to CLV3, is expressed in the SAM in differentiating cells in a pattern complementary to that of CLV3. CLE40 promotes WUS expression via BAM1, a CLV1-family receptor, and CLE40 expression is in turn repressed in a WUS-dependent manner. Together, CLE40-BAM1-WUS establish a second negative feedback loop. 

结论：We propose that stem cell homeostasis is achieved through two intertwined pathways that adjust WUS activity and incorporate information on the size of the stem cell domain, via CLV3-CLV1, and on cell differentiation via CLE40-BAM1.

 摘 要 

植物茎分生组织中的干细胞内稳态需要干细胞增殖和细胞分化之间的紧密协调。在拟南芥中，干细胞表达分泌十二肽CLV3，其从富含亮氨酸重复受体激酶CLV1处接受信号，并与其与CLV1家族成员一起，下调homeodomain转录因子WUS的表达。WUS蛋白从干细胞域下方的细胞移动到分生组织顶端，促进干细胞，其与CLV3的表达一起，构成了一个负反馈调节环。但是，分生组织中心区域的干细胞活性如何与外缘的器官起始及细胞分化相互协调还不清楚。本文中，作者发现CLE40基因编码一个与CLV3近源的分泌多肽，在SAM中表达，并且在正在分化的细胞中表现出一种与CLV3表达互补的模式。CLE40通过一个CLV1家族受体，促进WUS的表达，并且CLE40的表达又会受到一种以WUS依赖方式的抑制。综上，CLE40-BAM1-WUS建立第二个负反馈调节环。作者认为拟南芥的茎尖分生组织通过CLV3-CLV1来作用于干细胞域的大小，通过CLE40-BAM1来作用于细胞的分化，如此借助两条相互交织的途径来维持WUS的活性和协调信息，从而达到干细胞内稳态。

 通讯作者 

** Rüdiger GW Simon **