Physical mapping and InDel marker development for the restorer gene Rf2 in cytoplasmic male sterile CMS-D8 cotton

BackgroundCytoplasmic male sterile (CMS) with cytoplasm from Gossypium Trilobum (D8) fails to produce functional pollen. It is useful for commercial hybrid cotton seed production. The restore line of CMS-D8 containing Rf(2) gene can restore the fertility of the corresponding sterile line. This study combined the whole genome resequencing bulked segregant analysis (BSA) with high-throughput SNP genotyping to accelerate the physical mapping of Rf(2) locus in CMS-D8 cotton.MethodsThe fertility of backcross population ((sterile linexrestorer line)xmaintainer line) comprising of 1623 individuals was investigated in the field. The fertile pool (100 plants with fertile phenotypes, F-pool) and the sterile pool (100 plants with sterile phenotypes, S-pool) were constructed for BSA resequencing. The selection of 24 single nucleotide polymorphisms (SNP) through high-throughput genotyping and the development insertion and deletion (InDel) markers were conducted to narrow down the candidate interval. The pentapeptide repeat (PPR) family genes and upregulated genes in restore line in the candidate interval were analysed by qRT-PCR.ResultsThe fertility investigation results showed that fertile and sterile separation ratio was consistent with 1:1. BSA resequencing technology, high-throughput SNP genotyping, and InDel markers were used to identify Rf(2) locus on candidate interval of 1.48Mb on chromosome D05. Furthermore, it was quantified in this experiment that InDel markers co-segregated with Rf(2) enhanced the selection of the restorer line. The qRT-PCR analysis revealed PPR family gene Gh_D05G3391 located in candidate interval had significantly lower expression than sterile and maintainer lines. In addition, utilization of anther RNA-Seq data of CMS-D8 identified that the expression level of Gh_D05G3374 encoding NB-ARC domain-containing disease resistance protein in restorer lines was significantly higher than that in sterile and maintainer lines.ConclusionsThis study not only enabled us to precisely locate the restore gene Rf(2) but also evaluated the utilization of InDel markers for marker assisted selection in the CMS-D8 Rf(2) cotton breeding line. The results of this study provide an important foundation for further studies on the mapping and cloning of restorer genes.

Automated summary

This study successfully located the restore gene Rf(2) within a candidate interval of 1.48Mb on chromosome D05 by investigating fertility ratios, using BSA resequencing technology, high-throughput SNP genotyping, and InDel markers. The study also found that InDel markers co-segregated with Rf(2), enhancing the selection of the restorer line.