Mapping of BnMs4 and BnRf to a common microsyntenic region of Arabidopsis thaliana chromosome 3 using intron polymorphism markers.

A recessive epistatic genic male sterile two-type line, 7365AB ( Bnms3ms3ms4msRrfRf/BnMs3ms3ms4ms4RfRf), combined with the fertile interim-maintainer 7365C ( Bnms3ms3ms4ms4rfrf) is an effective pollination control system in hybrid rapeseed production. We report an effective strategy used to fine map BnMs4 and BnRf. The two genes were both defined to a common microsyntenic region with Arabidopsis chromosome 3 using intron polymorphism (IP) markers developed according to Arabidopsis genome information and published genome organization of the A genome. The near-isogenic lines 7365AC ( Bnms3ms3ms4ms4Rfrf/ Bnms3ms3ms4ms4rfrf) of BnRf and 736512AB ( Bnms3ms3Ms4ms4RfRf/ Bnms3ms3ms4ms4RfRf) of BnMs4 were constructed to screen developed markers and create genetic linkage maps. Nine polymorphic IP markers (P1-P9) were identified. Of these, P2, P3, P4, and P6 were linked to both BnMs4 and BnRf with genetic distances <0.6 cM. Three simple sequence repeat markers, SR2, SR3, and SR5, were also identified by using public information. Subsequently, all markers linked to the two genes were used to compare the micro-collinearity of the regions flanking the two genes with Brassica rapa and Arabidopsis. The flanking regions showed rearrangements and inversion with fragments of different Arabidopsis chromosomes, but a high collinearity with B. rapa. This collinearity provided extremely valuable reference for map-based cloning in polyploid Brassica species. These IP markers could be exploited for comparative genomic studies within and between Brassica species, providing an economically feasible approach for molecular marker-assisted selection breeding, accelerating the process of gene cloning, and providing more direct evidence for the presence of multiple alleles between BnMs4 and BnRf. [ABSTRACT FROM AUTHOR]