The Role of Wrky Transcription Factor on Rapid Stomatal Closure Induced By Drought Stress in Cowpea.

Cowpea (Vigna unguiculata (L.) Walp.) is one of the highly drought tolerant legumes, and it is considered to be economic important in arid area. On the one hand, soybean (Glycine max (L.) Merr.) receives a great damage by drought stress because it is drought sensitive legume. Under drought stress condition, the stomatal closure of cowpea was faster than that of soybean (Itani et al. 1992), and the stomatal closure is induced by abscisic acid (ABA). Therefore, in order to analyze the drought tolerant mechanism in cowpea, we focused on the relationship between ABA and stomatal closure in comparison to soybean. Relative gene expression of 9-cis-epoxycarotenoid dioxygenase (NCED), a key enzyme in ABA biosynthesis, of both cowpea and soybean was measured. As a result, NCED expression of cowpea was elevated as a rapid response to drought stress as compared with that of soybean. Also, AtWRKY57 transcription factor responses to drought tolerance and it can directly bind to W-box of NCED3 promoter sequences (Yanjuan et al. 2014). To investigate whether WRKY could display similar to the behavior of NCED expression, we examined the transcript levels of WRKY of both cowpea and soybean. Consistent with NCED, WRKY expression of cowpea was earlier than that of soybean. In addition, ABA content of cowpea root accumulated more rapidly prior to drought stress. In summary, NCED and WRKY expression pattern in response to drought stress was at the same trend as ABA accumulation, and this response was observed to be more rapid stomatal closure in cowpea. Furthermore, WRKY might play a role at the upstream of ABA biosynthesis pathway under drought conditions. As a consequence, this accelerated mechanism in cowpea might lead to its high drought tolerance.

References: Itani et al. (1992) Jpn. J. Trop. Agr. 36: 269-274
Yanjuan et al. (2014) Molec. Plant 5: 1375-1388
Keywords: abscisic acid (ABA), drought tolerance, stomatal closure, NCED, WRKY