Molecular mapping of the suppressor gene Igc1 to the gametocidal gene Gc3-C1 in common wheat

Abstract

Several species of the genus Aegilops, wild relatives of wheat (Triticum aestivum, 2n = 6x = 42, AABBDD) carry gametocidal (Gc) genes. Gc genes kill the gametes without themselves by causing chromosomal breakage during postmeiotic cell divisions, and therefore are strong segregation distorters. The Gc gene Gc3-C1 derived from chromosome 3C of Ae. triuncialis (2n = 4x = 28, CCUU) induces chromosomal breakage in wheat cultivar 'Chinese Spring' (CS) but not in cultivar 'Norin 26' (N26). This cultivar-specific inhibition of Gc function is caused by a suppressor gene Igc1 located on chromosome 3B of N26. Igc1 is presumed to be a modified Gc gene without breakage function because of its homoeology to Gc3-C1. Here we report the results of linkage and physical mapping of Igc1 to help elucidate the molecular mechanisms underlying Gc action. Segregation analysis of the phenotypic data in BC 1 F 1 mapping population of the cross between (CSxN26)F 1 and CS + 3C" showed a 1:1 segregation ratio indicating that Igc1 is a dominant gene. In the linkage analysis, three molecular marker loci Xgwm285, Xgwm376, and Xcfp1886 cosegregated with the Igc1 locus. Bin mapping assigned the loci Xgwm285 and Xcfp1886 to bin C-3BS1-0.33 and Xgwm376 to bin C-3BL2-0.22. Physical mapping using Gc-induced chromosomal deletion lines of chromosome 3B of N26 revealed that the Igc1 locus resides in 52.0% or 2.1% of bins C-3BS1-0.33 and C-3BL2-0.22, respectively. Pericentromeric localization of Igc1 in chromosome 3B of N26 may have a positive effect to keep the two-component system of the Gc action. Map-based cloning approach to isolate the Igc1 may be difficult because recombination is depleted in the pericentromeric region. As is shown in this study, the combination of genetic and physical mapping offers high efficiency to identify the regions where genes are located especially in regions with low levels of recombination.

Cytological observation of chromosome breakage in wheat male gametophytes caused by gametocidal action of <i>Aegilops triuncialis</i>-derived chromosome 3C^t

“…In progeny of plants heterozygous for Igc1 and hemizygous for 3C t , Tsujimoto and Tsunewaki (1985b) cytologically identified aberrant chromosomes, such as telosomes and dicentrics. Recent work has mapped Igc1 to the pericentromeric region of chromosome 3B, suggesting that the gene is a homoeologous counterpart of Gc3-C t 1 that has lost Gc function (Yamano et al, 2010), as Gc3-C t 1 is also located in the pericentromeric region of 3C t (Endo, 2007). This conclusion had been earlier inferred based on chromosome homoeology (Tsujimoto and Tsunewaki, 1985a).…”

“…Plant materials To examine Gc action of 3C t and Igc1 inhibitory effects (Tsujimoto and Tsunewaki, 1985a;Yamano et al, 2010), we used the following six wheat lines: CS (2n = 42), euploid T. aestivum 'Chinese Spring'; DA3C t (2n = 44), disomic 3C t addition of CS; MA3C t (2n = 43), monosomic 3C t addition of CS; DS(3B CS )3C t (2n = 42), disomic substitution (3B)3C t of CS where chromosome 3B was substituted with 3C t ; MS(3B CS )3C t (2n = 42), monosomic substitution (3B)3C t of CS; and F 1 DS(3B CS )3C t × N26 (2n = 42), F 1 of DS(3B CS )3C t × N26. We then scored the proportion of normal pollen grains in anthers at the uninuclear stage, the proportion of mature pollen grains in their anthers at the dehiscence stage and the selfed-seed fertility.…”

“…Selfed-seed fertility We examined selfed-seed fertility during 2016-2017 for five to nine spikes per line. Selfedseed fertility was scored as previously described (Yamano et al, 2010) with minor modifications. Briefly, the number of seeds in the first and second florets was counted for ten spikelets excluding the two spikelets at the top and bottom of a given spike.…”

Gametocidal genes: from a discovery to the application in wheat breeding

“…However, semi-sterility did not appear in the common wheat cultivar Norin 26 (N26). Chromosome 3C t is preferentially transmitted to the next generation from both male and female sides in JF, but only from the female side in CS ( Endo and Katayama, 1978 ; Endo, 2007 ; Chen et al., 2008 ; Yamano et al., 2010 ). In the JF genetic background, both male and female gametes without chromosome 3C t were unsuccessful whereas, in the CS background, pollen without the Gc chromosome was functional.…”

Development of Wheat-Aegilops caudata Introgression Lines and Their Characterization Using Genome-Specific KASP Markers

“…Genomic rearrangements can be caused in Triticeae interspecific crosses due to gametocidal (Gc) chromosomes, also known as cuckoo chromosomes, which cause chromosome breakage, in the gametes that lack them (Endo, 1978;Finch et al, 1984;Nasuda et al, 1998;Friebe et al, 2000). Gc chromosomes have been found in many Aegilops species (Endo and Katayama, 1978;Endo, 1982Endo, , 2007 and in C-genome-derived allotetraploids where Gc action was found on chromosome 2C of Ae.…”