Progress 09/01/01 to 08/31/04
Outputs
Gametocidal (Gc) genes, introduced into common wheat from related Aegilops species, are selfish genetic elements that ensure their preferential transmission by inducing chromosome breaks. We have produced and characterized of a knock-out mutation of the Gc2 gene transferred to wheat as a wheat-Ae. sharonensis T4B-4Ssh translocation chromosome. In hemizygous Gc2/- condition, gametophytes lacking Gc2 suffer chromosome fragmentation and produce non-functional gametes, which leads to sporophytic semisterility and exclusive transmission of the Gc2-carrier chromosome. We have identified two EMS-induced Gc2 mutants that restore spike fertility and show Mendelian segregation. Progeny screening mapped both mutations to the Gc2-carrier chromosome T4B-4Ssh. C-banding and FISH 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 Gc2mut/- plants and C-banding analysis of testcross progenies
showed that no chromosome breakage occurs in the mutants. No gametophytic chromosome breakage was observed in heterozygous Gc2mut/Gc2 plants, which had fully fertile spikes. These results suggest that Gc2 encodes for two agents, one causing chromosome breaks in gametophytes lacking Gc2 and another that protects Gc2 carrier from breakage. The EMS-induced Gc2 mutants appear to be knock-outs of the gene encoding for the breaking agent.
Impacts
Gc genes may have played a significant role in karyotype evolution and speciation in the Triticum/Aegilops complex. This study is the first crucial step towards the cloning and molecular understanding of Gc2 action.
Publications
- Friebe B, Zhang P, Nasuda S, Gill BS, 2003. Characterization of a knock-out mutation at the Gc2 locus in wheat. Chromosoma 111: 509-517.
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Progress 01/01/03 to 12/31/03
Outputs
We have produced and characterized two knock-out mutation of the Gc2 gene transferred to wheat in the form of a wheat-Ae. sharonensis T4B-4Ssh#1 translocation chromosome. In hemizygous Gc2/- condition, gametophytes lacking Gc2 suffer chromosome fragmentation and produce non-functional gametes, which lead to sporophytic semisterility and exclusive transmission of the Gc2-carrier chromosome. We have identified two EMS-induced Gc2 mutants that restore spike fertility and show Mendelian segregation. Progeny screening mapped both mutations to the Gc2-carrier chromosome T4B-4Ssh#1. C-banding and FISH analyses showed that the loss of Gc2 function in the mutants is not caused by a terminal deficiency. Analysis of first and second pollen mitoses in Gc2mut#1/- and Gc2mut#2/- plants and C-banding analysis of testcross progenies showed that no chromosome breakage occurs in the mutants. Also, no gametophytic chromosome breakage was observed in heterozygous Gc2mut#1/Gc2 and
Gc2mut#2/Gc2 plants, which had fully fertile spikes. These results suggest Gc2 encodes for two agents, one causing chromosome breaks in gametophytes lacking Gc2 and another protects Gc2 carrier from breakage. Both EMS-induced Gc2 mutants appears to be knock-outs of the gene encoding for the breaking agent. A mapping population of about 2000 test-cross seeds was developed for the Gc2mut#1mutant, will allow construction of a high resolution map around the Gc2 locus.
Impacts
Gc genes may have played a significant role in karyotype evolution in the Triticum/Aegilops complex. This study is the first crucial step towards the molecular understanding of Gc2 action. An understanding of the mechanisms leading to Gc-induced gametophytic sterility also may impact on agricultural production and may be exploited in the production of hybrid wheat.
Publications
- No publications reported this period
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Progress 01/01/02 to 12/31/02
Outputs
Our previous work identified one EMS-induced mutation at the Gc2 locus, which was mapped to the Gc2-carrier chromosome T4B-4Ssh by progeny screening. Our data support the dual-function model of Gc action and suggest that the mutation is a knock-out at the gene encoding for a `breaking' agent, whereas the gene encoding for the `protecting' agent is functional. In a second round of mutagenesis, we identified three additional putative Gc2 mutants, and one of them was confirmed by progeny screening. This mutation is presently being characterized cytologically. Mapping populations for the Gc2mut#1 are being developed and will be available in the next growing season. In addition, genes have been identified that are differentially expressed during premeiotic and postmeiotic stages in hemizygous Gc2/- and Gc2mut#1/- plants that will be useful markers in our mapping experiments.
Impacts
Gametocidal genes introduced from related Aegilops species into bread wheat are selfish genetic elements that ensure their preferential transmission by causing chromosome breakage. The proposed research is aimed at producing knock-out mutations at the Gc2 locus that eventually lead to an understanding of Gc action at the molecular level and may also have an impact on wheat improvement.
Publications
- Friebe, B., Zhang, P., and Gill, BS. 2002 Characterization of a knock-out mutation at the Gc2 locus in wheat. Chromosoma, in press.
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Progress 01/01/01 to 12/31/01
Outputs
The specific objectives of this project are: to determine the chromosomal location of the Gc2 gene, to determine whether or not chromosome breakage occurs in the Gc2 mutant, and to develop mapping populations that will allow genetic mapping of the Gc2 mutant. By testcrossing and progeny screening we mapped the Gc2 mutant to the Gc2-carrier chromosome T4B-4Ssh. The analysis of the first and second pollen mitosis showed no chromosome breakage occurs in the Gc2 mutant. Progeny screening by C-banding analysis confirmed there is no chromosome breakage in the Gc2 mutant and, thus, the mutated Gc2-carrier chromosome segregates in a normal Mendelian fashion. In a second round of mutagenesis, we identified three additional Gc2 mutants that are presently being testcrossed to determine the chromosomal location of the mutant. Meiotic chromosome pairing and polymorphisms screening identified DA4Ssh#3, DA4Ssh#5, and DA4Ssh#7 as suitable for producing the mapping populations.
Impacts
Gametocidal genes were introgressed from related Aegilops species into bread wheat are selfish genetic elements that ensure their preferential transmission by causing chromosome breakage. The proposed research is aimed to produce knockout mutants at the Gc2 locus that will eventually lead to an understanding of Gc action at the molecular level and may also have an impact
Publications
- No publications reported this period
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