Gruhn Nijuscha, Halawa Mhyeddeen, Snel Berend, Seidl Michael F, Heyl Alexander
Institute of Biology/Applied Genetics, Dahlem Centre of Plant Sciences, Freie Universität, 14195 Berlin, Germany.
Plant Physiol. 2014 May;165(1):227-37. doi: 10.1104/pp.113.228080. Epub 2014 Feb 11.
The two-component signaling system--the major signaling pathway of bacteria--is found among higher eukaryotes only in plants, where it regulates diverse processes, such as the signaling of the phytohormone cytokinin. Cytokinin is perceived by a hybrid histidine (His) kinase receptor, and the signal is transduced by a multistep phosphorelay system of His phosphotransfer proteins and different classes of response regulators (RRs). To shed light on the origin and evolution of the two-component signaling system members in plants, we conducted a comprehensive domain-based phylogenetic study across the relevant kingdoms, including Charophyceae algae, the group of green algae giving rise to land plants. Surprisingly, we identified a subfamily of cytokinin receptors with members only from the early diverging land plants Marchantia polymorpha and Physcomitrella patens and then experimentally characterized two members of this subfamily. His phosphotransfer proteins of Charophyceae seemed to be more closely related to land plants than to other groups of green algae. Farther down the signaling pathway, the type-B RRs were found across all plant clades, but many members lack either the canonical Asp residue or the DNA binding domain. In contrast, the type-A RRs seemed to be limited to land plants. Finally, the analysis provided hints that one additional group of RRs, the type-C RRs, might be degenerated receptors and thus, of a different evolutionary origin than bona fide RRs.
双组分信号系统——细菌的主要信号传导途径——仅在高等真核生物的植物中发现，它在植物中调节多种过程，如植物激素细胞分裂素的信号传导。细胞分裂素由一种杂合组氨酸（His）激酶受体感知，信号通过His磷酸转移蛋白和不同类别的响应调节因子（RRs）的多步磷酸化中继系统进行转导。为了阐明植物中双组分信号系统成员的起源和进化，我们对包括轮藻纲藻类（产生陆地植物的绿藻群体）在内的相关界进行了全面的基于结构域的系统发育研究。令人惊讶的是，我们鉴定出一个细胞分裂素受体亚家族，其成员仅来自早期分化的陆地植物多歧苏铁和小立碗藓，然后对该亚家族的两个成员进行了实验表征。轮藻纲的His磷酸转移蛋白似乎与陆地植物的关系比与其他绿藻群体的关系更密切。在信号传导途径的下游，B型RRs在所有植物分支中都有发现，但许多成员要么缺少典型的天冬氨酸残基，要么缺少DNA结合结构域。相比之下，A型RRs似乎仅限于陆地植物。最后，分析表明，另一组RRs，即C型RRs，可能是退化的受体，因此其进化起源与真正的RRs不同。
