Phylogenetic and functional analysis of the WRKY gene family in rice

The analysis of the full genome sequence of rice highlights the presence of 107 genes encoding for transcription factors of the WRKY family. Those proteins have one or two ~70 aa consensus sequence characterized by a very highly conserved WRKYGQK motif together with a zinc-finger-like motif CX4-7-C23-28-H-X1-2-(H/C) that provides binding properties to DNA. Proteins containing two WRKY motifs usually have an N-terminal consensus sequence that is shorter and/or incomplete and does not appear to have a main role in DNA binding. Comparative phylogenetic analysis of this family in rice as well as in other organisms where WRKY genes were identified reveals that their ancient origin predates the divergence of plants and points out their later tremendous duplication in land plants and in particular in monocotyledonous and dicotyledonous plants. With the purpose of understanding a possible reason for this huge amplification, we are focussing on determining their function in rice, mainly following with 2 approaches: 1) analysis of insertion mutants; and 2) characterization of WRKY gene expression profile. Several groups developed insertion populations for rice, and we have been able to search for insertion in different members of this important gene family. Our screening led us to identify several rice-mutated lines containing an insertion in the coding and/ore in regulatory region of WRKY genes. We have focussed our attention toward 20 of such lines and we are currently analyzing their phenotypic response to four host and non-host strains of the main important rice pathogen Magnaporthe grisea. As for the second approach, we are currently performing a characterization of the expression profile of all the members of the family, analyzing several plant organs and different growth condition. A preliminary analysis of 28 WRKY genes allowed us to identify OsWRKY76 as induced by salicylic acid treatment, a signalling hormone often involved in response to stresses. For this gene an RNAi construct has been prepared and will be soon used to transform rice plants. At the moment an analysis of the whole gene family is going to be carried out using the oligo-macroarray techniques. (Texte intégral