Map and sequence-based chromosome walking towards cloning of the male fertility restoration gene Rf5 linked to R 11 in sunflower

The nuclear fertility restorer gene Rf5 in HA-R9, originating from the wild sunflower species Helianthus annuus , is able to restore the widely used PET1 cytoplasmic male sterility in sunflowers. Previous mapping placed Rf5 at an interval of 5.8 cM on sunflower chromosome 13, distal to a rust resistance gene R 11 at a 1.6 cM genetic distance in an SSR map. In the present study, publicly available SNP markers were further mapped around Rf5 and R 11 using 192 F 2 individuals, reducing the Rf5 interval from 5.8 to 0.8 cM. Additional SNP markers were developed in the target region of the two genes from the whole-genome resequencing of HA-R9, a donor line carrying Rf5 and R 11 . Fine mapping using 3517 F 3 individuals placed Rf5 at a 0.00071 cM interval and the gene co-segregated with SNP marker S13_216392091. Similarly, fine mapping performed using 8795 F 3 individuals mapped R 11 at an interval of 0.00210 cM, co-segregating with two SNP markers, S13_225290789 and C13_181790141. Sequence analysis identified Rf5 as a pentatricopeptide repeat-encoding gene. The high-density map and diagnostic SNP markers developed in this study will accelerate the use of Rf5 and R 11 in sunflower breeding.