Comparative analysis of the WRKY gene family between Chimonanthus praecox and C. salicifolius.

Abstract

Gene duplications provide evolutionary potentials for generating novel functions. Chimonanthus praecox and C. salicifolius are closely related species from Calycantaceae, Magnoliids. In this study, we compared the WRKY gene family from C. praecox and C. salicifolius, and predicted the potential gene function through gene expression patterns to explore the evolution of orthologous and paralogous gene pairs. A total of 73 and 85 WRKY genes were identified and analyzed from the whole genome sequencing of C. praecox and C. salicifolius. Based on the phylogenetic analysis, CpWRKY and CsWRKY genes were clustered into three groups (Group I、II、III) and 5 subgroups (Group IIa、IIb、IIc、IId、IIe). In C. praecox and C. salicifolius, we identified thirty-six and fifty-four pairs of WRKY segmental duplicated genes, respectively, along with two and three pairs of tandem duplicates, indicating that segmental duplication plays a crucial role in the evolution of Chimonanthus WRKY gene family. Most WRKY duplication gene pairs originated from segmental duplications before the first whole genome duplication (WGD), highlighting this period as a significant source of genetic diversity and functionality for the WRKY family. The analysis of WRKY gene expression levels suggests that CsWRKY18 and CsWRKY68 may promote the growth of the roots in C. salicifolius. Comparisons of expression profiles between species revealed that five orthologous gene pairs presented identical expression trends, indicating functional conservation and absence of neo-functionalization or sub-functionalization. However, most orthologous gene pairs exhibit differences in expression patterns, suggesting that they have undergone functional divergence. This functional differentiation may be due to the different selective pressures faced by C. praecox and C. salicifolius during their speciation processes. This study provided detailed information on the WRKY gene family from C. praecox and C. salicifolius, and a new insight for studying gene duplication and function evolution.