Characterization of a knock-out mutation at the Gc2 locus in wheat

Abstract

Gametocidal (Gc) genes, introduced into common wheat from related Aegilops species, are selfish genetic elements that ensure their preferential transmission by inducing chromosomal breaks. Here we report the production and characterization of a knock-out mutation of the Gc2 gene transferred to wheat as a wheat-Aegilops sharonensis T4B-4S(sh)#1 translocation chromosome. In hemizygous Gc2/- condition, gametophytes lacking Gc2 suffer chromosomal fragmentation and produce non-functional gametes, which leads to sporophytic semisterility and exclusive transmission of the Gc2-carrier chromosome. We have identified one putative ethyl methylsulfonate (EMS)-induced Gc2 mutant that restores spike fertility and shows Mendelian segregation. Progeny screening mapped the mutation to the Gc2-carrier chromosome T4B-4S(sh)#1. C-banding and fluorescence in situ hybridization analyses showed that the loss of Gc2 function in the mutant is not due to a terminal deficiency. Analysis of first and second pollen mitoses in Gc2(mut) /- plants and C-banding analysis of testcross progenies showed that no chromosomal breakage occurs in the mutant. No gametophytic chromosomal breakage was observed in heterozygous Gc2(mut) /Gc2 plants, which had fully fertile spikes. These results suggest that Gc2 encodes two agents, one causing chromosomal breaks in gametophytes lacking Gc2 and another that protects the Gc2 carrier from breakage. The EMS-induced Gc2 mutant appears to be a knock-out of the gene encoding the "breaking" agent. These data are a first crucial step toward the molecular understanding of Gc2 action.

Gene evolution at the ends of wheat chromosomes

“…sharonensis DS4S sh #7(4B) and homozygous translocation stock T4BS.4BL-4S sh #1L plants (48) followed by a cross of the F 1 with CS. The second genetic mapping population used was a 50-line subset of the recombinant inbred 150-line International Triticeae Mapping Initiative population Synthetic ϫ Opata 85 (49).…”

The Evolution of Sex-Independent Transmission Ratio Distortion Involving Multiple Allelic Interactions at a Single Locus in Rice

“…In these loci, a wide array of compatible alleles conferring compatibility to a wide range of strains has been proposed, and some have actually been mapped ( Ji et al 2005;Qiu et al 2005;Wang et al 2006). However, regarding the wide compatibility proposed in rice, whether these compatible alleles act specifically on the alleles at their own locus or on sterility genes at different loci, as reported in wheat (Tsujimoto and Tsunewaki 1985;Friebe et al 2003) and Drosophila (Lyttle 1991;Temin et al 1991), is not known. In the testcross experiments, the hybrids between the S 6 n carriers and the tester lines did not necessarily exhibit a higher seed-setting rate than the hybrids between S 6 or S 6 a carriers and the tester lines (Table 2).…”

“…TRD systems often involve alleles at a minimum of two closely linked loci, a distorter and its cis-acting target (Lyttle 1991). Examples of the TRD system of this type include the mouse t-haplotype (Silver 1993), segregation distorter (SD) of Drosophila (Temin et al 1991), and Gametocidal 2 (Gc2) in wheat (Friebe et al 2003).…”

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

“…Chromosomal location of Igc1 on chromosome 3B of N26 (Tsujimoto and Tsunewaki, 1985) suggested that Gc3-C1 and the Igc1 are homoeologous genes and Igc1 may be a modified Gc gene that have the 'protecting' function but not the 'breaking' function (Tsujimoto, 2005). This relationship between Gc3-C1 and Igc1 is analogous to that between Gc2 and its mutant allele Gc2 mut (Friebe et al, 2003). The Gc2 mut allele does not exert chromosome breaking function but fully protects chromosomes from breaking.…”

“…According to the dual function model for Gc action suggested by Endo (1990), Gc genes consist of two factors, one of which confers 'breaking' function and another 'protecting' function. This model is supported by the findings of the inhibitor of a Gc gene (Tsujimoto and Tsunewaki, 1985) and the isolation of a mutant that only lost 'breaking' function (Friebe et al, 2003). However, the molecular mechanism of Gc action has not been unraveled yet.…”