Identification of a novel haplotype of the Ms locus controlling restoration of male-fertility and its implication in origination of cytoplasmic male-sterility in onion (Allium cepa L.)

Abstract

ABSTRACT Seeds of F1 hybrid cultivars of onions have been exclusively produced by utilising cytoplasmic male-sterility (CMS). A single locus, Ms, controls restoration of male-fertility of CMS onions. When a molecular marker tagging the AcPMS1 gene, a candidate gene for the Ms locus, was used to genotype diverse breeding lines, an unusual marker genotype showing an intermediate size of PCR product was identified in one breeding line (ORI854). The male-fertility phenotype of ORI854 was all male-sterile. Full-length genomic DNA sequence (16,464 bp) of this novel AcPMS1 allele from ORI854 was more closely related to a recessive AcPMS1 allele than to a dominant allele. However, there were more than 200 polymorphic sequences between this novel allele and the recessive allele, indicating that this novel AcPMS1 allele might not have recently diverged from the recessive allele. Phylogenetic analysis implied that onion male-sterility might have first appeared in a common ancestor before divergence of this novel allele and recessive allele of AcPMS1. Analysis of full-length cDNA sequences of additional 12 genes showing almost perfect linkage disequilibrium with the Ms locus indicated that no recombination might have happened among 13 genes including AcPMS1 in the novel Ms haplotype after divergence from the recessive Ms haplotype.