Analysis of the Wsi18, a stress-inducible promoter that is active in the whole grain of transgenic rice

There is currently a shortage of efficient promoters for stress-inducible gene expression, especially in monocotyledonous crops. Here, we report analysis of the rice Wsi18 promoter, a member of the group 3 Lea family, in transgenic rice plants. The abundance of Wsi18 mRNA increased in leaf tissues within 2 h of exposure to NaCl or abscisic acid (ABA) and within 6 h of exposure to drought, but there was no transcript increase in response to low-temperature conditions. Wsi18 mRNA accumulated in the roots similarly to in the leaves, but at a faster rate. The promoter was linked to the GFP reporter gene, transformed into rice, and its activity was analyzed in transgenic plants at all stages of plant growth from calli, vegetative tissues, flowers, and to dry seeds, both before and after stress treatment. The activity of the promoter was significantly increased in the whole plant body, including flowers, on exposure of plants to stress conditions, with very low levels of basal activity in all tissues. Moreover, the promoter was found to be predominantly active in the whole grain, including endosperm, embryo, and aleurone layer during seed development. Together, we have identified and analyzed the Wsi18 promoter and found a previously undescribed characteristic-a stress-inducible property in the whole plant body with activity in the whole grain during seed development.