Through activating specifi c transcriptional programmes, plants can launch resistance mechanisms to stressful environments and acquire a new equilibrium between development and defence. To screen the rice WRKY transcription factor which functions in abiotic stress tolerance and modulates the abscisic acid (ABA) response, we generated a whole array of 35S-OsWRKY transgenic Arabidopsis. In this study, we report that 35S-OsWRKY72 transgenic Arabidopsis, whose seed germination was retarded under normal conditions, emerged more sensitive to mannitol, NaCl, ABA stresses and sugar starvation than vector plants. Meanwhile, 35S-OsWRKY72 transgenic Arabidopsis displayed early fl owering, reduced apical dominance, lost high temperature-induced hypocotyl elongation response, and enhanced gravitropism response, which were similar to the auxin-related gene mutants aux1, axr1 and bud1. Further, semi-quantitative RT-PCR showed that the expression patterns of three auxin-related genes AUX1, AXR1 and BUD1 were signifi cantly altered in rosette leaves and infl orescences of 35S-OsWRKY72 plants compared with control Arabidopsis, and two ABA-related genes ABA2 and ABI4 were induced in 35S-OsWRKY72 seedlings. In addition, northern blot analysis indicated that, in rice, OsWRKY72 was inducible by polyethylene glycol (PEG), NaCl, naphthalene acetic acid (NAA), ABA and 42°C, similar to its orthologue AtWRKY75 in Arabidopsis, implying that these two WRKY genes might be required for multiple physiological processes in their plants. Together, these results suggest that OsWRKY72 interferes in the signal cross-talk between the ABA signal and auxin transport pathway in transgenic Arabidopsis.

Acta Botanica Yunnanica, 2008, 30:600--705

Overexpression of OsWRKY72 Gene Causes Auxin Signaling Passway in Arabidopsis

The transcription factors WRKY protein superfamily are widely presented in plants. It is well known that a majority of the plant biological processes are modulated by WRKY transcription factors. And here we focused on OsWRKY72. Genetic analysis showed the apical dominance of 35S:OsWRKY72 transgenic Arabidopsis thaliana was repressed and the transgenic plants had significantly more shoot branches comparing with the control plants. Besides the reduced apical dominance, the phenotypes , including curled leaves and short fruits in transgenic Arabidopsis, were similar to those of the characteristic mutants deficiency in auxin singal transduction . These results suggested that OsWRKY72 played an important role in the auxin signaling pathway.