Research PaperRapid alkalinization factor (RALF) genes are related to genic male sterility in Chinese cabbage (Brassica rapa L. ssp. pekinensis)

•Characteristics of the RALF gene family in Brassica rapa were studied via bioinformatic analysis.•Using RNA-Seq techniques, 14 RALF differentially expressed genes were identified.•qRT-PCR revealed differences in RALF expression between male sterile and male fertile buds in four genic male sterility AB lines of Brassica rapa.•This study lays the foundation to study the roles of RALF genes in pollen development in Brassica rapa.

Male sterility is commonly and widely used for hybrid seed production in Brassica rapa L. ssp. pekinensis (B. rapa), and some genes related to anther and pollen development may play significant roles in pollen fertility. Hence, in this study, we performed whole-genome scanning and identified 38 genes from the RALF gene family in B. rapa, which were grouped into four clades according to the phylogenetic tree. Thirty-six of the sequences contained only exons; the other two contained both exonic and intronic sequences. Conserved motifs of the 38 RALF genes were identified. The Ka/Ks ratios of duplicated RALF gene pairs were less than 1, indicating that they had gone through purifying selection. Moreover, a total of 14 RALF-like differentially expressed genes (DEGs) were identified by RNA-Seq between male fertile and male sterile buds, and all were highly or specifically expressed in male fertile buds of the AB line 'AB01'. A qRT-PCR analysis confirmed that the expression patterns of the 14 RALF DEGs in the AB line 'AB01' were similar to those in the other three genic male sterility (GMS) AB lines 'AB02', 'AB03', and 'AB04', indicating that the RALF genes may be related to pollen development in B. rapa. Meanwhile, the results of qRT-PCR validated the RNA-Seq transcriptome as accurate and reliable. This study will provide valuable information for exploring the molecular mechanism underlying sterility in GMS AB lines of B. rapa.