Abstract
Cytoplasmic male sterility (CMS) is an important feature for achieving heterosis in the development of hybrid crops. Mitochondria contribute to CMS, especially via mitochondrial DNA (mtDNA) rearrangements and chimeric genes. However, the mechanisms of CMS have not been fully elucidated, and the isonuclear alloplasmic lines used in previous studies have limited utility in cotton CMS research. In this study, three CMS lines (J4A-1, J4A-2 and J4A-3) and their isoplasmic maintainer line (J4B) were analyzed for mtDNA structural differences via high-throughput sequencing. The results showed that mtDNA was conserved (with similarities higher than 99%) among the three CMS lines and their isoplasmic maintainer line. All lines harbored 36 known protein-coding genes, 3 rRNAs, and 15 tRNAs. The protein-coding genes with non-synonymous mutations mainly encoded two types of proteins: ATPase and ribosomal proteins. Four new open reading frames (ORFs) (orf116b, orf186a-1, orf186a-2 and orf305a) were identified as candidate ORFs responsible for CMS. Two of the ORFs (orf186a-1 and orf186a-2) were identified as orf4 and orf4-2 of the upland cotton CMS line 2074A (a line with Gossypium harknessii Brandegee CMS-D2-2 cytoplasm), respectively. These findings provide a reference for CMS research in cotton or other crops.
Highlights
Cytoplasmic male sterility (CMS) refers to the loss of stamen function and pollination ability and is very important in the production of crop hybrids, such as rice, corn, and wheat [1,2,3]
Among these open reading frames (ORFs), we focused on the unique ORFs of the CMS lines compared and J4B, respectively
Among these ORFs, we focused on the unique ORFs of the CMS lines compared with the maintainer line J4B (Supplementary Tables S8 and S9 and Table 4)
Summary
Cytoplasmic male sterility (CMS) refers to the loss of stamen function and pollination ability and is very important in the production of crop hybrids, such as rice, corn, and wheat [1,2,3]. Previous studies have revealed that CMS results from interactions between mitochondrial genes and nuclear genes [4], and the abnormal development of pollen is usually associated with defects in mitochondria. Mitochondria are essential, semi-autonomously replicating organelles that produce energy and encode for limited genetic information. Agronomy 2020, 10, 765 plant mitochondrial genomes (mt genomes) depend on highly integrated functional coordination with the nucleus. Many essential genes are transferred to the host’s nuclear genome or are lost, the mt genome remains complete [5]. The mt genomes of animals are small, ranging from 15–18 kb, whereas the mt genomes of plants have evolved to vary greatly in size since the initial symbiosis between eukaryotic cells and α-proteobacteria [6]. The size of angiosperm mitochondrial DNA (mtDNA) ranges from 208 kb (Brassica hirta) to 11.3 Mb (Silene conica) [5,7,8]
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