Unique fertility restoration suppressor genes for male-sterile CMS ANN2 and CMS ANN3 cytoplasms in sunflower (Helianthus annuus L.)

Abstract

Single dominant fertility restoration (Rf) genes for cytoplasmic male-sterile (CMS) sunflower lines CMS ANN2 and CMS ANN3 were previously identified in three and five sources, respectively. However, expressions of the dominant Rf genes were suppressed when crossing restoration lines with three inbred lines. Preliminary results indicated that segregation of fertility in most testcross progeny families from crosses of half-diallel F1’s of restoration lines with the two CMS lines, respectively, did not agree with those of the F2 generation of the half-diallel crosses. In this study, using selected CMS ANN2 and CMS ANN3 plants without the silencing suppressor (S) genes, we confirmed the existence of S genes in the nuclear genomes of the CMS lines used for crossing of the two CMS cytoplasms. Inheritance study suggested that Rf gene suppression was controlled by a single dominant gene in specific backgrounds, whereas two to three complementary S genes could exist in certain backgrounds. Using testcross population Rf ANN2-P21/RHA 274//Rf ANN2-P21, a single S gene from RHA 274, designated S1, was mapped to a recombination suppressed region on the sunflower linkage group (LG) 3, co-segregating with 16 SSR or single nucleotide polymorphism (SNP) markers, flanked by NSA_003339 and ORS124 at a distance of 1.4 and 0.7 cM, respectively. These molecular markers will potentially assist in identifying lines without suppressor genes, including CMS lines. Unique suppression of Rf genes confirmed existence of suppressor (S1) gene in CMS lines that mapped to a recombination suppressed region on linkage group 3, which will enhance understanding of cytoplasm-nuclear interactions.