Chan Ju Lim

Arabidopsis DREB2C functions as a transcriptional activator of HsfA3 during the heat stress response

The dehydration-responsive element binding protein (DREB) family is important in regulating plant responses to abiotic stresses. DREB2C is one of the Arabidopsis class 2 DREBs and is induced by heat stress (HS). Here, we present data concerning the interaction of DREB2C with heat shock factor A3 (HsfA3) in the HS signal transduction cascade. RT-PCR showed that HsfA3 is the most up-regulated gene among the 21 Arabidopsis Hsfs in transgenic plants over-expressing DREB2C. DREB2C and HsfA3 displayed similar transcription patterns in response to HS and DREB2C specifically transactivated the DRE-dependent transcription of HsfA3 in Arabidopsis mesophyll protoplasts. Yeast one-hybrid assays and invitro electrophoretic mobility shift assays further showed that DREB2C interacts with two DREs located in the HsfA3 promoter with a binding preference for the distal DRE2. Deletion mutants of DREB2C indicated that transactivation activity was located in the C-terminal region. In addition, dual activator-reporter assays showed that the induction of heat shock protein (Hsp) genes in transgenic plants could be attributed to the transcriptional activity of HsfA3. Taken together, these results indicate that DREB2C and HsfA3 are key players in regulating the heat tolerance of Arabidopsis.

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.

Overexpression of Arabidopsis dehydration-responsive element-binding protein 2C confers tolerance to oxidative stress

Dehydration-responsive element-binding proteins (DREBs) regulate plant responses to environmental stresses. In the current study, transcription of DREB2C, a class 2 Arabidopsis DREB, was induced by a superoxide anion propagator, methyl viologen (MV). The oxidative stress tolerance of DREB2C-overexpressing transgenic plants was significantly greater than that of wild-type plants, as measured by ion leakage and chlorophyll fluorescence under light conditions. The transcriptional activity of several ascorbate peroxidase (APX) genes as well as APX protein activity was induced in DREB2C overexpressors. Additionally, the level of H2O2 in the overexpressors was lower than in wt plants under similar oxidative stress conditions. An electrophoretic mobility shift assay and transient activatorreporter assay showed that APX2 expression was regulated by heat shock factor A3 (HsfA3) and that HsfA3 is regulated at the transcriptional level by DREB2C. These results suggest that DREB2C plays an important role in promoting oxidative stress tolerance in Arabidopsis.