Divergent evolutionary patterns of the MAPK cascade genes in Brassica rapa and plant phylogenetics.

Mitogen-activated protein kinase (MAPK) cascade signal transduction modules play crucial roles in regulating many biological processes in plants. These cascades are composed of three classes of hierarchically organized protein kinases, MAPKKKs, MAPKKs and MAPKs. Here, we analyzed gene retention, phylogenetic, evolution and expression patterns of MAPK cascade genes in Brassica rapa. We further found that the MAPK branches, classes III and IV, appeared after the split of bryophytes and green algae after analyzing the MAPK cascade genes in 8 species, and their rapid expansion led to the great size of the families of MAPKs. In contrast, the ancestral class I subfamily of MAPKK gene families have been highly conserved from algae to angiosperms. For the MAPKKK family, the MEKK and Raf subfamily share a common evolutionary origin, and Raf plays a major role in the expansion of the MAPKKK gene family. The cis-elements and interaction network analyses showed the important function of MAPK cascade genes in development and stress responses in B. rapa. This study provides a solid foundation for molecular evolution analyses of MAPK cascade genes.

丝裂原活化蛋白激酶（MAPK）级联信号转导模块在调节植物的许多生物学过程中起着至关重要的作用。这些级联由三类分级组织的蛋白激酶组成，即MAPKKKs、MAPKKs和MAPKs。在此，我们分析了白菜（Brassica rapa）中MAPK级联基因的基因保留、系统发育、进化和表达模式。我们进一步发现，在分析了8个物种的MAPK级联基因后，MAPK分支中的III类和IV类在苔藓植物和绿藻分化之后出现，并且它们的快速扩增导致了MAPKs家族的庞大。相比之下，MAPKK基因家族的祖先I类亚家族从藻类到被子植物都高度保守。对于MAPKKK家族，MEKK和Raf亚家族有共同的进化起源，并且Raf在MAPKKK基因家族的扩增中起主要作用。顺式作用元件和互作网络分析表明MAPK级联基因在白菜的发育和胁迫应答中具有重要功能。这项研究为MAPK级联基因的分子进化分析提供了坚实的基础。