Plant genes with meiotic function: from their identification toward biotech exploitation

Meiosis is a specialized cell division, consisting of two successive divisions without intervening DNA synthesis, that is crucial in the sexual reproduction. Peculiar features of meiosis are pairing and crossovers between homologous chromosomes, as well as random segregation of homologs. The knowledge of the genetic control of meiosis is useful to provide new tools for plant breeding. Indeed, a deep understanding of the mechanisms controlling genetic recombination and chromosome assortment would allow breeders to manipulate genetic diversity and genetic uniformity. In particular, increase/decrease and redistribution of crossovers as well as meiotic nuclear restitution modes in 2n gametes pave the way to control the transmission of valuable traits. Based on this premise, the aim of the present work was the identification of genes involved in plant meiotic processes such as recombination and nuclear restitution, which are of interest for plant breeding, by using the model organism Arabidopsis thaliana and potato. Most of the work performed in Arabidopsis was supported by the European Project “Systematic Analysis of Factors Controlling Meiotic Recombination in Higher Plants (MeioSYS)” which points to the identification and analysis of histone modifiers controlling frequency and distribution of meiotic crossovers in plants. Through an in silico analysis based on the identification of genes overexpressed in reproductive tissues and on similarity to genes involved in reproduction in other model organisms, the histone acetylases HAG2, HAG1, HAM1 and HAF1 and the histone deacetylases HDA7, HDA6, HDA9 and HDA19 have been identified as candidates for a meiotic role in Arabidopsis. In this PhD thesis, HDA7 was functionally characterized by loss-of-function and gain-of-function mutants. Reduced seed set and embryo sac degeneration were observed in knock-down mutants allowing to conclude that HDA7 is required for female gamethophyte development. Moreover, HDA7 has a role in embryo and plant development as highlighted by the reduced germination rate and the altered post-germination growth observed in knock-down and overexpressing mutants. Candidate genes which could be involved in hda7 phenotype were also provided paving the way to a deeper understanding of the molecular role of HDA7 in plant reproduction and development. The meiotic function of HDA7 is currently under investigation to assess whether megasporogenesis defects are associated to embryo sac collapse and to verify if meiotic recombination is changed in microsporocytes. The work performed on a diploid potato clone was aimed to the identification of PARALLEL SPINDLES (PSL) genes, which could be involved in 2n pollen production as showed for Arabidopsis thaliana PS1. By means of molecular and in silico analyses, the presence of at least three PSL loci in the potato genome was showed. Moreover, the candidate locus that likely has a role in 2n pollen production was provided. The existence of PSLs throughout Viridiplantae, from mosses to higher plants, was also showed. PSLs occur mostly as singleton in the analyzed genomes except in soybean and potato both characterized by a recent whole genome duplication event. A useful insight into evolutionary conservation of FHA and PINc domains throughout plant PSLs was provided suggesting a fundamental role of these domains for PSL function.