ABSTRACT

Shoot meristems contain stem cells, and they sustain growth and development of the above-ground tissues in land plants. The HAIRY MERISTEM (HAM) family genes, encoding GRAS-domain transcriptional regulators, play essential roles in the control of shoot meristem development and stem cell homeostasis in several flowering plants. Similar to other GRAS proteins, the C-terminal regions of HAM family proteins across land plants are conserved, containing signature motifs that define the GRAS domain. In contrast, the N-terminal regions of HAM family proteins display substantial divergence in sequence and length. Whether the variable and divergent N-termini are required for the conserved functions of HAM proteins is unknown. Our recent work showed that CrHAM – the HAM homolog in the fern Ceratopteris richardii was able to replace the role of type-II HAM genes in Arabidopsis, maintaining established shoot apical meristems and promoting the initiation of new stem cell niches. Here, we provide additional information and show that CrHAM contains a much longer N-terminal region compared to Arabidopsis HAM proteins, which is conserved among different fern HAM homologs. The deletion of this region largely compromises the ability of CrHAM to replace the function of Arabidopsis HAM proteins in shoot meristems. These new data together with previous results suggest that, although lacking the sequence conservation among HAM homologs from different plant lineages, the N-termini are important for the conserved functions of HAM family proteins.

摘要

枝条分生组织含有干细胞，它们维持陆地植物地上组织的生长和发育。HAIRY MERISTEM ( HAM ) 家族基因编码 GRAS 结构域转录调节因子，在控制几种开花植物的枝条分生组织发育和干细胞稳态中发挥重要作用。与其他 GRAS 蛋白类似，跨陆地植物的 HAM 家族蛋白的 C 末端区域是保守的，包含定义 GRAS 结构域的特征基序。相反，HAM 家族蛋白的 N 末端区域在序列和长度上表现出显着差异。HAM 蛋白的保守功能是否需要可变和不同的 N 末端是未知的。我们最近的工作表明CrHAM——蕨类植物Ceratopteris richardii中的HAM同源物能够取代拟南芥中 II 型HAM基因的作用，维持已建立的茎尖分生组织并促进新干细胞生态位的启动。在这里，我们提供了额外的信息并表明 CrHAM 包含比拟南芥 HAM 蛋白更长的 N 末端区域，该区域在不同的蕨类 HAM 同源物中是保守的。该区域的缺失在很大程度上损害了 CrHAM 取代拟南芥 HAM 蛋白在茎分生组织中的功能的能力。这些新数据与以前的结果一起表明，尽管来自不同植物谱系的 HAM 同源物之间缺乏序列保守性，但 N 末端对于 HAM 家族蛋白的保守功能很重要。