Developmentally regulated expression of the rice calmodulin promoter in transgenic tobacco plants

Abstract

To study the expression of rice calmodulin genes (RCaM-1 and RCaM-2), rice calmodulin promoters were fused with reporter genes (CAT and GUS) and introduced into tobacco cells. The expression of chimeric rice CaM promoter-cat gene in transgenic tobacco plants showed that both CaM promoters are expressed in all tissues tested, including the reproductive organs. However, RCaM-1 and RCaM-2 promoter activity had differential levels of expression. RCaM-1 promoter is strongly expressed largely in flowers and young seeds in comparison to other parts of transgenic plants, whereas RCaM-2 promoter is strongly expressed in young petioles and stems in comparison to other parts of the transgenic plants. RCaM-2 promoter, which has a comparatively higher level of expression than RCaM-1 promoter, was used to investigate the effects of auxin and light on calmodulin gene expression in transgenic plants. RCaM-2 promoter activity was strongly increased with auxin-treatment, and was also slightly enhanced under dark conditions. The expression of RCaM-2 promoter was remarkably induced with sucrose or salicylic acid treatment but not ethephon. Strong GUS staining was observed in meristemic tissue such as stem apex, petiole and root tips. These results suggest that the calmodulin gene may play a vital role in the signal transduction process and cell growth.