The Functional Analysis Of Transcriptional Factors: OsWRKY23 And AtWRKY14

Plant regulatory mechanisms are often controlled at the level of transcription factors. The WRKY superfamily of plant transcription factors is one such group of proteins with potential regulatory roles pertaining to a variety of biotic and abiotic stress responses. WRKY proteins contain a conserved amino acid sequence WRKYGQK and a novel zinc-finger-like motif Cys2His2 or Cys2HisCys.13 cDNAs encoding WRKY proteins were isolated from rice cDNA library constructed from 4℃-treated shoot according to the conserved WRKY domain. 9 of 13 WRKY cDNA clones (OsW8,12,13,14,16,17,23,26 and 45) had a high copy number (roughly 10—30 positive clones/108 cDNA library clones) in the cold-treated library, but another 4 WRKY cDNAs(OsW9,21,24 and 30) had a low amount of copies (roughly 5—10 positive clones/1010 cDNA library clones). These results showed that the expression of the 9 WRKY genes might be induced by stress and play regulatory roles in response to various abiotic stresses in rice. Northern blotting analysis revealed that 10 of 13 WRKY genes were differentially regulated in the plants treated by four abiotic stresses, including salt、drought cold (4℃) and heat (42℃), but the expression profiles have a great difference among them not only by different abiotic stress factors but also during different treated time courses. The difference of gene expression profiles suggested the different physiological functions among WRKY genes. One of the ten genes, OsWRKY23 expressed exclusively in roots and senescing leaves under normal growth conditions. Under biotic and abiotic stresses treatments,OsWRKY23 was markedly induced by continuous-dark-induced leaf senescence and infection by rice pathogen Pyricularia oryzae Cav as well as salicylic acid (SA). Further analysis of OsWRKY23 overexpression Arabidopsis plants showed that OsWRKY23 might play a positive role in SA-mediated signaling pathways, and over-expression of the gene could have a positive impact on SA-mediated defense mechanisms and thus enhance plant resistance to P. syringae. We also observed that, after Botrytis infection, the 35S:WRKY23 plants showed similar disease symptoms and similar expression of PDF1.2, a molecular marker of the JA- and ET-mediated defense response signaling pathways (Zheng et al.2006). This observation suggests that OsWRKY23 is not involved in response to Botrytis mediated mainly by JA/ET signaling. Although high levels of production of OsWRKY23 can be beneficial in plant pathogen responses, it also carries some costs. In my work, I have found that transgenic plants expressing high levels of this protein exhibited more sensitive to continuous-dark induced senescence, whereas it responded normally to ACC treatment. In conclusion, these results suggest that OsWRKY23 is a novel modulator of pathogen responses as well as dark-induced leaf senescence.Also I analyzed the function of Arabidopsis AtWRKY14, a TMV-Cg induced transcriptional factor. Plants can fight infection if they possess resistance genes that are effective against invading viruses (Baker et al., 1997), by dramatic changes in these genes expression. In this work, we found that AtWRKY14 was induced by TMV-Cg in local and systemic leaves. Overexpression of AtWRKY14 inhibited the spread of TMV-Cg and mutation of this gene increased the spread speed. We suggest that AtWRKY14 is a positive regulator required for resistance to virus TMV-Cg.