Genome-Wide Investigation and Expression Analysis of K+-Transport-Related Gene Families in Chinese Cabbage (Brassica rapa ssp. pekinensis)

Potassium (K+) transport and channel systems play vital roles in plant growth, development and responses to various stresses. In this study, 44 putative K+-transport-related genes (18K+ uptake permease (KUP)/high-affinity K+ (HAK)/K+ transporter (KT) family genes and 26 channel genes, including 18 Shaker family genes and 8K+ channel outward (KCO) family genes) were identified in the genome of Chinese cabbage (Brassica rapa ssp. pekinensis). To clarify the molecular evolution of each family in Chinese cabbage, phylogenetic analysis and assessments of the gene structures, conserved motifs, chromosomal locations, gene duplications, expression patterns and cis-acting elements of the 44 putative K+-transport-related genes were performed. The phylogenetic analysis showed that these genes could be classified into five clades [KUP/HAK/KTs, KCOs, Kout, Kin (KAT) and Kin (AKT)] and that the members of a given clade shared conserved exon–intron distributions and motif compositions. These K+-transport-related genes were unevenly distributed over all ten chromosomes, including four duplicated gene pairs that implied an expansion of K+-transport-related genes in Chinese cabbage. Analyses of Illumina RNA-seq data for these 44K+-transport-related genes indicated tissue-/organ-specific expression patterns. In addition, an overall evaluation showed that the expression levels of KUP/HAK/KT genes were significantly higher than those of potassium channel genes in six tissues. Promoter cis-acting element analysis revealed that these 44K+-transport-related genes may be associated with responses to 10 abiotic stresses, primarily light, methyl jasmonate (MeJA) and abscisic acid (ABA). Our results provide a systematic and comprehensive overview of K+-transport-related gene families in Chinese cabbage and establish a foundation for further research on K+ absorption and transport functions.