Nad7: A Candidate Gene Responsible for Cytoplasmic Male Sterility in Pigeonpea (Cajanas cajan)

Cytoplasmic male sterility (CMS) has been extensively exploited in commercial pigeonpea hybrid breeding system, however molecular mechanism responsible behind this system is unknown. To understand the underlying molecular mechanism involved in A₄ CMS system, 34 genes were analyzed for length variation and expression profiling between CMS line (ICPA 2039) and its maintainer (ICPB 2039). As a result, nad4l showed 13.6 folds higher expression in CMS line as compared to its maintainer and nad7a showed 10bp deletion between these lines. Protein structure evaluation of amplicons of nad4l and nad7a for ICPA 2039 and ICPB 2039 revealed conformational changes for nad7a indicating its association with CMS. While analyzing this gene across different CMS lines derived from A₄ system, the 10 bp deletion was found in all the CMS lines.  Furthermore, analysis of 10 bp deletion across different CMS systems (A₁-A₈) showed specificity of this deletion to only A₄ CMS. In summary, this study provided strong clue for involvement of the 10 bp deletion in nad7a gene with the A₄ CMS system as well as diagnostic molecular marker for purity assessment of CMS lines.