Genome-wide identification and evolution of WNK kinases in Bambusoideae and transcriptional profiling during abiotic stress in Phyllostachys edulis

With-no-lysine (WNK) kinases play vital roles in abiotic stress response, circadian rhythms, and regulation of flowering time in rice, Arabidopsis, and Glycine max. However, there are no previous reports of WNKs in the Bambusoideae, although genome sequences are available for diploid, tetraploid, and hexaploid bamboo species. In the present study, we identified 41 WNK genes in five bamboo species and analysed gene evolution, phylogenetic relationship, physical and chemical properties, cis-elements, and conserved motifs. We predicted the structure of PeWNK proteins of moso bamboo and determined the exposed, buried, structural and functional amino acids. Real-time qPCR analysis revealed that PeWNK5, PeWNK7, PeWNK8, and PeWNK11 genes are involved in circadian rhythms. Analysis of gene expression of different organs at different developmental stages revealed that PeWNK genes are tissue-specific. Analysis of various abiotic stress transcriptome data (drought, salt, SA, and ABA) revealed significant gene expression levels in all PeWNKs except PeWNK11. In particular, PeWNK8 and PeWNK9 were significantly down- and up-regulated, respectively, after abiotic stress treatment. A co-expression network of PeWNK genes also showed that PeWNK2, PeWNK4, PeWNK7, and PeWNK8 were co-expressed with transcriptional regulators related to abiotic stress. In conclusion, our study identified the PeWNKs of moso bamboo involved in circadian rhythms and abiotic stress response. In addition, this study serves as a guide for future functional genomic studies of the WNK genes of the Bambusoideae.