Identification of Rf9, a Gene Contributing to the Genetic Complexity of Fertility Restoration in Hybrid Wheat

Abstract

Wheat (Triticum aestivum L.) is a self-pollinating crop whose hybrids offer the potential to provide a major boost in yield. Male sterility induced by the cytoplasm of Triticum timopheevii is a powerful method for hybrid seed production. Hybrids produced by this method are often partially sterile, and full fertility restoration is crucial for wheat production using hybrid cultivars. To identify the genetic loci controlling fertility restoration in wheat, we produced two cytoplasmic male-sterile (CMS) backcross (BC1) mapping populations. The restorer lines Gerek 79 and 71R1203 were used to pollinate the male-sterile winter wheat line CMS-Sperber. Seed set and numbers of sterile spikelets per spike were evaluated in 340 and 206 individuals of the populations derived from Gerek 79 and 71R1203, respectively. Genetic maps were constructed using 930 and 994 single nucleotide polymorphism (SNP) markers, spanning 2,160 and 2,328 cM over 21 linkage groups in the two populations, respectively. Twelve quantitative trait loci (QTL) controlled fertility restoration in both BC1 populations, including a novel restorer-of-fertility (Rf) locus flanked by the SNP markers IWB72413 and IWB1550 on chromosome 6AS. The locus was mapped as a qualitative trait in the BC1 Gerek 79 population and was designated Rf9. One hundred-nineteen putative candidate genes were predicted within the QTL region on chromosome 6AS. Among them were genes encoding mitochondrial transcription termination factor and pentatricopeptide repeat-containing proteins that are known to be associated with fertility restoration. This finding is a promising step to better understand the functions of genes for improving fertility restoration in hybrid wheat.

Identification of Rf Genes in Hexaploid Wheat (Triticumaestivum L.) by RNA-Seq and Paralog Analyses

“…The dominance of Rf8 localized on chromosome 2DS was verified by Sinha et al [36]. Another major dominant restorer gene, Rf9, was detected in the subtelomeric region of chromosome 6AS [39]. Melonek et al [47] recently identified Rf1 and Rf3 via genetic mapping, comparative sequence analyses, and functional studies.…”

“…To date, eight fertility restorer genes (Rf1-Rf6 and Rf8-Rf9) that restore the production of normal pollen in wheat with the T. timopheevii sterilizing cytoplasm have been identified and mapped on the following seven wheat chromosomes: 1A (Rf1), 1BS (Rf3), 2DS (Rf8), 6A (Rf6), 6AS (Rf9), 6B (Rf6 and Rf4), 6D (Rf5), 7B (Rf7), and 7D (Rf2) [29][30][31][32][33][34][35][36][37][38][39]. There is some uncertainty regarding the nomenclature of Rf2, Rf3, Rf4, and Rf6 [40].…”

“…The donors of dominant Rf3 alleles include wheat cultivar Primépi, which also contains Rf6 [41], and the spelt cultivars Badenkrone, Badenstern, and Schwabenspelz [31,40,43]. The Rf3 gene was reported as dominant, but it is suppressed by a weak fertility suppressor gene on chromosome 7D [31,39,43].…”

“…Several quantitative trait loci (QTLs) for general fertility restoration were also mapped on wheat chromosomes 1AS, 1BS, 2DS, 4BS, 6AS, 6BS, 7AL, and 7D at positions overlapping Rf genes [39,46,[49][50][51][52]. Additionally, several fertility-related QTLs were localized to regions that were not reported to carry Rf genes (i.e., 1DS, 2AL, 2BS, 4AL, 4BS, 5A, 5BL, and 7AL) [39,49,50,52].…”

Male Fertility Genes in Bread Wheat (Triticum aestivum L.) and Their Utilization for Hybrid Seed Production

“…However, there are certain aspects of CMS systems, including timopheevii CMS, that render these systems more complex for hybrid seed production in wheat. First, various studies have revealed that combinations of two or three and perhaps more Rf genes are needed for complete fertility restoration of CMS in wheat [ 75 , 76 , 77 ]. To add to that complexity, epistatic interactions among Rfs and between Rfs and modifier loci have also been highlighted by several studies [ 78 ].…”