The WRKY transcription factor superfamily: its origin in eukaryotes and expansion in plants

Abstract

BackgroundWRKY proteins are newly identified transcription factors involved in many plant processes including plant responses to biotic and abiotic stresses. To date, genes encoding WRKY proteins have been identified only from plants. Comprehensive search for WRKY genes in non-plant organisms and phylogenetic analysis would provide invaluable information about the origin and expansion of the WRKY family.ResultsWe searched all publicly available sequence data for WRKY genes. A single copy of the WRKY gene encoding two WRKY domains was identified from Giardia lamblia, a primitive eukaryote, Dictyostelium discoideum, a slime mold closely related to the lineage of animals and fungi, and the green alga Chlamydomonas reinhardtii, an early branching of plants. This ancestral WRKY gene seems to have duplicated many times during the evolution of plants, resulting in a large family in evolutionarily advanced flowering plants. In rice, the WRKY gene family consists of over 100 members. Analyses suggest that the C-terminal domain of the two-WRKY-domain encoding gene appears to be the ancestor of the single-WRKY-domain encoding genes, and that the WRKY domains may be phylogenetically classified into five groups. We propose a model to explain the WRKY family's origin in eukaryotes and expansion in plants.ConclusionsWRKY genes seem to have originated in early eukaryotes and greatly expanded in plants. The elucidation of the evolution and duplicative expansion of the WRKY genes should provide valuable information on their functions.

A Novel WRKY-like Protein Involved in Transcriptional Activation of Cyst Wall Protein Genes in Giardia lamblia

“…It has not been identified to date in yeast or animal genomes (33). However, it has been recently found in nonplant eukaryotic organism Dictyostelium discoideum and G. lamblia (33).…”

“…WRKY factors have been identified as downstream components of a defense-and pathogeninduced mitogen-activated protein kinase (MAPK) 2 signaling pathway in plants (39,40). A putative wrky gene has been identified in G. lamblia genome (33). The WRKY domains of the giardial WRKY protein are highly similar to those of the group I WRKY protein (33).…”

“…A putative wrky gene has been identified in G. lamblia genome (33). The WRKY domains of the giardial WRKY protein are highly similar to those of the group I WRKY protein (33).…”

“…This search detected one putative homologue for WRKY that has been reported previously (GenBank TM accession number XM_ 001708755; open reading frame 9237 in the G. lamblia genome data base) (33). The WRKY coding region with 324 nucleotides of 5Ј-flanking regions was cloned, and the nucleotide sequence was determined.…”

“…The mRNA levels of these wrky genes also increased in response to these changing environments (30,32). The wrky gene family has been found in many plants but has not been identified to date in yeast or animal genomes (33). The WRKY domain consists of ϳ60 amino acid residues and has a conserved WRKYGQK sequence followed by a zinc finger-like motif (27).…”