Transcriptomics And Metabolomics Studies On Cytoplasmic Male Sterility In Cotton

Male sterility is the failure of plants to produce functional anthers, pollen, or male gametes. Cytoplasmic male sterility (CMS) is total or partial male sterility associated with plant biology as the result of specific nuclear and mitochondrial interactions. CMS not only has very important application value in heterosis utilization, but also has been an ideal material for nucleus-cytoplasm interaction research. Although the molecular mechanisms underlying cotton CMS has not been revealed completely at present, most research results indicate that the CMS gene is located on mitochondrial genome, and that the rearrangement of the mitochondrial genome sequence leads to mitochondrial dysfunction in CMS line which subsequently triggers strong retrograde regulation to nuclear genome expression and results in male sterility. Our previous studies demonstrated that cytoplasmic retrograde regulation is probably a principal molecular mechanism for CMS in cotton. CMS line and its maintainer of cotton are two isonuclear-alloplasmic lines, so studies on the differences of gene expression profiles of the anthers allow us to evaluate the retrograde regulation of CMS gene, and thus help to unravel the molecular mechanisms for CMS in cotton. Metabolome, as the final products of genome expression, directly defines the biochemistry characteristics of a cell or tissue, so metabolomic data can be used to better explain the biochemical mechanisms for CMS formation. Nevertheless, integrated transcriptome and metabolome analysis opens an avenue to illustrate gene to metabolite networks more precisely and thus will be an effective strategy for deciphering the mechanisms for CMS formation and regulation in cotton.In the present study, the upland cotton CMS line of Zhongmiansuo12A whose cytoplasm is derived from104-7A and the maintainer line of Zhongmiansuo12were employed as research materials, the transcriptomes of their anthers were profiled and compared by using Illumina next sequencing technology. A total of3190genes were identified to be differentially expressed between the CMS and maintainer lines (P<0.001,|log2Ratio|≥1). The results of Go annotation and GO term enrichment of the differentially genes indicated that these genes mainly participated in carbohydrate metabolism, fatty acid metabolism, biosynthesis and metabolism of secondary metabolites, especially phenylpropanoid metabolism, phenylpropanoid biosynthesis, and flavonoid biosynthesis, etc. The differentially expressed genes were also mapped onto these pathways by MapMan tools. Among them,474genes are transcription factor belonging to57families including bHLH, C3H, MYB-related, PHD, MADS, Ap2-EREBP, FAR1, mTERF, WRKY, Orphans, MYB, C2H2, NAC, TRAF, ABI3VP1, and Tify et al., suggesting that retrograde regulation is primarily performed at transcriptional level. In addition.146differentially expressed genes are related to biosynthesis, signaling transduction and plant responsive reaction of phytohomones, including ethylene, auxin, abscisic acid, gibberellin, cytokinin, salicylic acid, jasmonic acid and brassinosteroid.The metabolites accumulated in the anthers of the CMS and maintainer lines were isolated and identified by using derivatization procedures followed by gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) respectively.141chromatography peaks were repeatedly detected by GC-MS analysis, among them,82peaks were identified to match a known compound with at least70%similarity by database searching,43compounds showed to be differentially accumulated in two materials. They are mainly carbohydrates, organic acids, amino acids, etc. involving biosynthesis of plant hormones, biosyntheis of secondary compounds, eg. phenylpropanoids, ABC transporters related pathways, and aromatic amino acid (phenylalanine and tyrosine) metabolism. LC-MS analysis was implemented both in positive ion mode and negative ion mode,2403and2313peaks were detected with at least70%similarity respectively. Peaks with score>90coupled with difference fold>32were chosen to search against database,255and207components were identified respectively, among them,31components were up-regulated while431components were down-regulated in CMS compared to those in the maintainer. These metabolites are mainly phenylpropanoids, flavonoids, and terpenoids, etc. which are involved in the biosyntheses of secondary metabolites such as phenylpropanoid and flavonoid.By integration of transcriptome and metabolome analyses, the decreased accumulation of phenylpropanoids and flavonoids resulted from the compromised biosynthesis pathways coupled with enhanced metabolism pathways of them in the anthers of CMS line may contribute largely to cytoplasmic male sterility in104-7A of cotton.