Integrated analysis of transcriptome and proteome changes related to the male-sterile mutant MS7-2 in wucai (Brassica Campestris L.)

Male sterility is a complex developmental process involving the differentiation of different tissues and the co-ordinated expression of genes. It is not only used to produce hybrids with effective utilization of heterosis but also an ideal tool to study plant development networks. Here, we carried out morphological and cytological observations on the flower buds of the previously studied male-sterile mutant MS7-2 and its wild-type fertile plant MF7-2 at different developmental stages and performed transcriptomic and proteomic analyses. Compared with the anthers of MF7-2, the anthers of MS7-2 were obviously atrophied, the anther surface was concave, the tapetum was abnormally expanded at the mononuclear microspore stage and normal pollen grains could not be produced. Proteomic analysis showed that the differentially expressed proteins (DEPs) were mainly involved in lipid transport, lipid binding and lipase activity and were mainly concentrated in carbohydrate metabolism, biosynthesis of other secondary metabolites and lipid metabolism. Transcriptomic results showed that the differentially expressed genes (DEGs) were mainly related to cell membrane components and were significantly enriched in carbohydrate metabolism, lipid metabolism, membrane transport and other pathways. In addition, transcription factors involved in anther and pollen development were also found to be significantly down-regulated in MS7-2, such as AMS, bHLH66, bHLH69 and WRKY 34. Weighted gene coexpression network anal-ysis (WGCNA) screened two key modules of anther abortion in wucai. The DEGs in the two modules were mainly enriched in the "terpenoid backbone biosynthesis," "pentose and glucuronate interconversions" and "cutin, suberine and wax biosynthesis" pathways, and three hub genes were screened as BraA02g028550.3C (LACS5), BraA01g016670.3C (VHA-G3) and BraA03g043400. 3C (AMS). Through transcriptomic and proteomic analyses, a regulatory network of MS7-2 male sterility of was constructed. It is speculated that the down-regulation of these genes and proteins in MS7-2 anthers inhibits the synthesis of some lipids and endogenous metabolites and ac-cumulates a large amount of reactive oxygen species (ROS) in the tapetum, leading to the failure of normal PCD and the abortion of MS7-2. This study provides new insights into the molecular mechanism of male sterility in wucai.