Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN, 47907, USA.
Purdue Center for Plant Biology, Purdue University, West Lafayette, IN, 47907, USA.
Plant J. 2021 Apr;106(2):366-378. doi: 10.1111/tpj.15169. Epub 2021 Mar 27.
The shoot apical meristems (SAMs) of land plants are crucial for plant growth and organ formation. In several angiosperms, the HAIRY MERISTEM (HAM) genes function as key regulators that control meristem development and stem cell homeostasis. To date, the origin and evolutionary history of the HAM family in land plants remains unclear. Potentially shared and divergent functions of HAM family members from angiosperms and non-angiosperms are also not known. In constructing a comprehensive phylogeny of the HAM family, we show that HAM proteins are widely present in land plants and that HAM proteins originated prior to the divergence of bryophytes. The HAM family was duplicated in a common ancestor of angiosperms, leading to two distinct groups: type I and type II. Type-II HAM members are widely present in angiosperms, whereas type-I HAM members were independently lost in different orders of monocots. Furthermore, HAM members from angiosperms and non-angiosperms (including bryophytes, lycophytes, ferns and gymnosperms) are able to replace the role of the type-II HAM genes in Arabidopsis, maintaining established SAMs and promoting the initiation of new stem cell niches. Our results uncover the conserved functions of HAM family members and reveal the conserved regulatory mechanisms underlying HAM expression patterning in meristems, providing insight into the evolution of key stem cell regulators in land plants.
陆生植物的茎尖分生组织（SAM）对于植物生长和器官形成至关重要。在几种被子植物中，HAIRY MERISTEM（HAM）基因作为关键调节因子，控制分生组织发育和干细胞稳态。迄今为止，HAM 家族在陆生植物中的起源和进化历史尚不清楚。HAM 家族成员在被子植物和非被子植物中的潜在共有和分歧功能也尚不清楚。在构建 HAM 家族的综合系统发育树时，我们表明 HAM 蛋白广泛存在于陆生植物中，并且 HAM 蛋白起源于苔藓植物分化之前。HAM 家族在被子植物的共同祖先中发生了复制，导致了两个不同的组：I 型和 II 型。II 型 HAM 成员广泛存在于被子植物中，而 I 型 HAM 成员则在单子叶植物的不同目中独立丢失。此外，来自被子植物和非被子植物（包括苔藓植物、石松植物、蕨类植物和裸子植物）的 HAM 成员能够替代拟南芥中 II 型 HAM 基因的作用，维持已建立的 SAM 并促进新的干细胞龛的启动。我们的研究结果揭示了 HAM 家族成员的保守功能，并揭示了 HAM 在分生组织中表达模式的保守调控机制，为陆生植物中关键干细胞调节因子的进化提供了新的视角。
