Enhancing the Rate of Meiotic Crossing-Over for Plant Breeding

Abstract

Meiotic recombination contributes to the generation of biodiversity as well as to genome stability, ensuring the proper segregation of homo logs during meiosis. It is also an essential step in the process of plant breeding. It generates the diversity needed by the breeder for selection of novel varieties. In this project, we have collaborated towards the goals to identify and characterize key genes involved in meiotic recombination. In addition we have shown how some of these genes can be used, through loss of function, or through overexpression, to enhance homologous recombination in Arabidopsis and in maize. Our main achievements can be summarized as follows: 1- To establish a collection of mutants, in Arabidopsis and in maize for candidate genes. In Arabidopsis, insertion mutants were isolated in the following genes: AtMSHI, AtMSH4, AtMSH5, AtMLH3, AtPHSl, and mutants in the Mre11/Rad50/Nbs1 complex. In maize, the TILLING system was established and enabled to isolate mutants in candidate genes, such as Rad2l-4a, Sgo2, and Aml. In addition, we generated phs 1 mutant alleles as well as mutants in the Mre11/Rad50/Nbs1 complex. No mus8l mutants have been found thus far. 2- We showed that mutants in AtMLH3 have decreased rates of crossover, suggesting that overexpression of these genes may enhance crossover. Mutants in AtMSHlhad no effect and mutants in AtMSH4 and 5 showed sterility. Overexpression of these genes might also enhance crossover. The effect of other mutations on crossovers in maize is still being investigated. 3- We showed that overexpression of AtMLH1, RecG and RuvC under a meioticspecific promoter enhances meiotic crossover in Arabidopsis. The effect of PHSloverexpression on crossover is expected to be determined soon. 4- New tools have been developed and perfected to study the recombination genes effect on meiotic crossovers. This includes antibodies, cDNAs and fusion proteins.