Pectin methylesterase inhibitor (PMEI) family can be related to male sterility in Chinese cabbage (Brassica rapa ssp pekinensis)

Pectin-related genes play significant roles in pollen development and pollen tube growth, and their allelic variations are one of the major reasons for the abnormal development of male gametophyte. Currently, little is known about the role of the PMEI family in male sterility of plants. In this study, 97 putative PMEI genes were identified in Brassica rapa genome. By a phylogenetic analysis, the PMEI family was divided into 10 clades with highly conserved structural characteristics. The publically available RNA-seq data on different tissues of B. rapa accession Chiifu-401-42 revealed that 23 PMEI isoforms were flower-specific genes. We created a recessive genic male sterile mutant (ftms) in Chinese cabbage. This mutant was a doubled haploid line with stable inheritance, derived from Chinese cabbage 'FT' generated through a combination of radiation mutagenesis and isolated microspore culture. The transcriptome profiles of the floral buds of ftms and its wild-type line 'FT' were determined using RNA-seq. A total of 17 PMEI genes were found to be differentially expressed; all of them were down-regulated in ftms compared to their levels in 'FT'. Consistent with the transcriptome data, all these genes were observed to be highly expressed in the floral buds of 'FT' using qRT-PCR analysis. Of these, eight genes were specifically expressed in the floral buds of 'FT'; three of these (Bra019903, Bra014099, and Bra032239) were stamen-specific genes. The results contribute to further elucidation of the regulatory mechanisms underlying male sterility in Chinese cabbage.