Cytoplasmic male sterility (CMS) is a convenient model for studying the interactions between nuclear and mitochondrial genes in plants and an effective tool for producing heterotic hybrid seeds. A significant number of different types of CMS-inducing cytoplasms have been identified in sorghum, with restoration of male fertility in each type controlled by strictly specific fertility restorer genes (Rf, restorers-of-fertility). To identify the chromosomal localization of fertility restorer genes for the 9E type CMS of sorghum, we studied the amplification patterns of several SSR markers located on chromosome 2 of the sorghum genome in plants with different fertility levels from the F2 hybrid population (9E Pishchevoe 614 × no. 151/20). It was established that the SSR markers sam60498 and sam26858a, localized on chromosome 2 in the region of 23 371 194–23 911 554 bp, are associated with fertility restoration in this type of CMS, with fertile F2 plants being homozygotes characterized by amplicons of these markers 220 or 150 bp in size, respectively. The results of cytological analysis of F1 hybrid pollen, the inheritance of SSR markers associated with male fertility restoration, and the segregation pattern for male fertility among F2 plants indicate that a gametophytic restorer gene, for which the symbol Rf-9E1 has been proposed, is involved in fertility restoration. It is assumed that a possible candidate for the role of the restorer gene is the PPR gene 002G142700.1, localized at positions 23 810 047–23 812 824 bp of chromosome 2, closely linked to the sam26858a marker. Analysis of the recombination frequency among fertile plants between the Rf-9E1 gene and the associated SSR markers did not reveal plants heterozygous for sam26858a; at the same time, the recombination frequency with sam60498 was 5.38%. Screening of 12 sorghum varieties and breeding lines with primers to the sam60498 marker revealed that all accessions unable to restore male fertility in F1 hybrids carried a “sterile” allele (≈180 bp), whereas varieties capable of full or partial fertility restoration (Perspektivnyi 1, Magistr, Azart) yielded a larger amplicon, ≈220 bp or similar in size. The study proposes a three-gene model for the genetic control of male fertility restoration in the 9E cytoplasm, involving the major gametophytic fertility restorer gene Rf-9E1 and two weaker sporophytic fertility restorer genes Rf-9E2 and Rf-9E3, interacting via recessive epistasis with the Rf-9E1 gene. The relationship between the localization of the putative Rf-9E1 restorer gene in the region of pericentromeric heterochromatin and the unstable nature of its expression, which depends on environmental conditions, is discussed.
Elkonin et al. (Wed,) studied this question.