Distinct expression patterns of two Arabidopsis phytocystatin genes, AtCYS1 and AtCYS2, during development and abiotic stresses.

The phytocystatins of plants are members of the cystatin superfamily of proteins, which are potent inhibitors of cysteine proteases. The Arabidopsis genome encodes seven phytocystatin isoforms (AtCYSs) in two distantly related AtCYS gene clusters. We selected AtCYS1 and AtCYS2 as representatives for each cluster and then generated transgenic plants expressing the GUS reporter gene under the control of each gene promoter. These plants were used to examine AtCYS expression at various stages of plant development and in response to abiotic stresses. Histochemical analysis of AtCYS1 promoter- and AtCYS2 promoter-GUS transgenic plants revealed that these genes have similar but distinct spatial and temporal expression patterns during normal development. In particular, AtCYS1 was preferentially expressed in the vascular tissue of all organs, whereas AtCYS2 was expressed in trichomes and guard cells in young leaves, caps of roots, and in connecting regions of the immature anthers and filaments and the style and stigma in flowers. In addition, each AtCYS gene has a unique expression profile during abiotic stresses. High temperature and wounding stress enhanced the expression of both AtCYS1 and AtCYS2, but the temporal and spatial patterns of induction differed. From these data, we propose that these two AtCYS genes play important, but distinct, roles in plant development and stress responses.