Abstract:

WRKY genes encode plant specific transcription factors that have been extensively studied in dicotyledonous plant species. To investigate the function of these genes in monocots, we isolated a full length cDNA clone of the rice WRKY gene which we tentatively named as OsiWRKY. The open reading frame of OsiWRKY cDNA encoded a polypeptide of 482 amino acid residues. The deduced primary structure of OsiWRKY contained a single WRKY domain of a typical C₂-H₂ zinc finger motif. A putative nuclear localization signal was also predicted in OsiWRKY. Potential targeting of OsiWRKY to the nucleus was confirmed by transient expression of an OsiWRKY::GFP fusion protein in rice cells. The recombinant OsiWRKY protein bound specifically to the W-box element in electrophoretic mobility shift assay. In inoculation experiments with Xanthomonas oryzae pv. oryzae, OsiWRKY transcription was increased more dramatically in the resistant variety IR-26 than in the susceptible variety Jingang 30. Interestingly, an increase in OsiWRKY transcription was also observed in the mock-inoculated control plants of both IR-26 and Jingang 30. However, the induction of OsiWRKY transcription occurred much earlier and more substantial in pathogen-infected plants than in mock-inoculated controls. These results suggest that OsiWRKY encodes a potential WRKY transcription factor that may function in responses of rice plants to both pathogen attack and mechanical wounding. But the mechanisms underlying the function of OsiWRKY in the two processes may be different.

Key words: transcription factor, WRKY, zinc finger, Oryza sativa, W-box