Functional analysis of six drought-inducible promoters in transgenic rice plants throughout all stages of plant growth

There are few efficient promoters for use with stress-inducible gene expression in plants, and in particular for monocotyledonous crops. Here, we report the identification of six genes, Rab21, Wsi18, Lea3, Uge1, Dip1, and R1G1B that were induced by drought stress in rice microarray experiments. Gene promoters were linked to the gfp reporter and their activities were analyzed in transgenic rice plants throughout all stages of plant growth, from dry seeds to vegetative tissues to flowers, both before and after drought treatments. In fold induction levels, Rab21 and Wsi18 promoters ranged from 65- and 36-fold in leaves to 1,355- and 492-fold in flowers, respectively, whereas Lea3 and Uge1 were higher in leaves, but lower in roots and flowers, as compared with Rab21 and Wsi18. Dip1 and R1G1B promoters had higher basal levels of activity under normal growth conditions in all tissues, resulting in smaller fold-induction levels than those of the others. In drought treatment time course, activities of Dip1 and R1G1B promoters rapidly increased, peaked at 2 h, and remained constant until 8 h, while that of Lea3 slowly yet steadily increased until 8 h. Interestingly, Rab21 activity increased rapidly and steadily in response to drought stress until expression peaked at 8 h. Thus, we have isolated and characterized six rice promoters that are all distinct in fold induction, tissue specificity, and induction kinetics under drought conditions, providing a variety of drought-inducible promoters for crop biotechnology.