Abstract
BackgroundWucai (Brassica campestris L. ssp. chinensis var. rosularis Tsen) is a variant of nonheading Chinese cabbage (Brassica campestris L.), which is one of the major vegetables in China. Cytoplasmic male sterility (CMS) has been used for Wucai breeding in recent years. However, the underlying molecular mechanism of Wucai CMS remains unclear. In this study, the phenotypic and cytological features of Wucai CMS were observed by anatomical analysis, and a comparative transcriptome analysis was carried out to identify genes related to male sterility using Illumina RNA sequencing technology (RNA-Seq).ResultsMicroscopic observation demonstrated that tapetum development was abnormal in the CMS line, which failed to produce fertile pollen. Bioinformatics analysis detected 4430 differentially expressed genes (DEGs) between the fertile and sterile flower buds. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed to better understand the functions of these DEGs. Among the DEGs, 35 genes (53 DEGS) were implicated in anther and pollen development, and 11 genes were involved in pollen cell wall formation and modification; most of these showed downregulated expression in sterile buds. In addition, several genes related to tapetum development (A6, AMS, MS1, MYB39, and TSM1) and a few genes annotated to flowering (CO, AP3, VIN3, FLC, FT, and AGL) were detected and confirmed by qRT-PCR as being expressed at the meiosis, tetrad, and uninucleate microspore stages, thus implying possible roles in specifying or determining the fate and development of the tapetum, male gametophyte and stamen. Moreover, the top four largest transcription factor families (MYB, bHLH, NAC and WRKY) were analyzed, and most showed reduced expression in sterile buds. These differentially expressed transcription factors might result in abortion of pollen development in Wucai.ConclusionThe present comparative transcriptome analysis suggested that many key genes and transcription factors involved in anther development show reduced gene expression patterns in the CMS line, which might contribute to male sterility in Wucai. This study provides valuable information for a better understanding of CMS molecular mechanisms and functional genome studies in Wucai.
Highlights
Wucai (Brassica campestris L. ssp. chinensis var. rosularis Tsen) is a variant of nonheading Chinese cabbage (Brassica campestris L.), which is one of the major vegetables in China
In the basic helix-loop-helix (bHLH) and MYB transcription factor families, a total of 43 differentially expressed genes (DEGs) were associated with 16 bHLH and 13 MYB transcription factors, and 10 bHLHs (15 DEGs) and 8 MYBs (16 DEGs) were downregulated in sterile buds, respectively (Fig. 4, Table 3). These differentially expressed transcription factors might result in abortion of pollen development in Wucai
A cytological examination was further carried out to evaluate the differences in pollen development between the fertile and sterile lines, and we observed that anther abortion occurred consistently in the sterile line, in which the tapetum developed abnormally and the microspore began to degrade after the meiotic stage (Fig. 1i-l)
Summary
Wucai (Brassica campestris L. ssp. chinensis var. rosularis Tsen) is a variant of nonheading Chinese cabbage (Brassica campestris L.), which is one of the major vegetables in China. Rosularis Tsen) is a variant of nonheading Chinese cabbage (Brassica campestris L.), which is one of the major vegetables in China. Rosularis Tsen) is a variant of nonheading Chinese cabbage (Brassica campestris L.), which is the most important species in the Brassicaceae family [1]. Anther and pollen development is a critical phase in the plant life cycle, which contains a series of correlated events involving a diverse range of genes in complex regulatory networks [7,8,9]. Dysfunction of these genes may lead to male sterility [10]. Many of these genes have been isolated and analyzed to have vital roles in CMS, the regulatory network and the novel genes underlying CMS occurrence are still largely unknown [8, 10]
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