The cotton mitochondrial chimeric gene orf610a causes male sterility by disturbing the dynamic balance of ATP synthesis and ROS burst

Plant cytoplasmic male sterility(CMS) is maternally inherited and often manifested as aborted pollen development, but the molecular basis of abortion remains to be identified. To facilitate an investigation of CMS in cotton, the complete sequence of cotton mitochondrial(mt) genome for CMS-D2 line ZBA was determined. The mt genome was assembled as a single circular molecule with 634,036 bp in length. A total of 194 ORFs, 36 protein-coding genes, six r RNAs, and 24 t RNAs were identified. Several chimeric genes encoding hypothetical proteins with transmembrane domains were identified. Among them, a previously unknown chimeric gene, orf610a, which is composed of atp1 and a 485-bp downstream sequence of unknown nature, was identified. RT-PCR and q RT-PCR validation indicated that orf610a was expressed specifically in a sterile line. Ectopic expression of orf610a in yeast resulted in excessive accumulation of reactive oxygen species and reduction in ATP content, in addition to inhibition of cellular growth.Transgenic A. thaliana overexpressing orf610a fused with a mitochondrial targeting peptide displayed partial male sterility. Interaction between ORF610a and the nuclear-encoded protein RD22 indicated an association between ORF610a and pollen abortion. Positive feedback during transcriptional regulation between nuclear regulatory factors and the mt CMS gene may account for the male sterility of ZBA.