Poster: Genome evolution

Abs # 848: The origin and expansion of the WRKY transcription factor family

Presenter:	Zhang, Yuanji , yjzhang@noble.org
Authors	Zhang, Yuanji  (A)   Wang, Liangjiang  (A)
Affiliations:	(A): The Samuel Roberts Noble Foundation

WRKY proteins are newly identified transcription factors primarily involved in the regulation of plant defense processes. Genes for WRKY proteins have been cloned from a number of flowering plants, and sequence similarity comparisons indicate that the Arabidopsis genome may encode over 70 WRKY genes. Since WRKY homologues have only been identified from plants, WRKY factors are believed to be plant-specific. We searched all publicly available sequence data, and did not find WRKY homologues in Archaea and Bacteria. We identified a single WRKY homologue from two non-plant species, including the primitive eukaryote Giardia lamblia. The genome of the unicellular green alga Chlamydomonas reinhardtii, an early branching of plants, also appears to encode a single WRKY gene. WRKY factors from these three species appear to be two-WRKY-domain proteins. Multiple WRKY genes are present in the Physcomitrella moss, which is an early-diverged land plant. The evolutionarily advanced flowering plants seem to have a large WRKY family, most of whose members have a single-WRKY domain. Our results indicate that the WRKY transcription factor family may have an early origin in eukaryotes and may have experienced tremendous gene duplications during the evolution of plants. We also cataloged the WRKY family for the rice genome where over 100 family members were identified. Our comparative analyses of WRKY genes from rice, Arabidopsis, the green alga and the two non-plant species suggest that genes encoding a single-WRKY-domain may have derived from the C-terminal domain of two-WRKY-domain encoding genes, and that WRKY domains may be classified into five phylogenetic groups. We propose a model for the evolution of the WRKY factor family.