Plants frequently encounter unfavorable conditions that adversely affect their growth, development, and productivity.  How plants sense, transduce and response to abiotic stresses is a fundamental question that is of tremendous significance for the future of agriculture.  My research focuses on understanding how plants cope with environmental stresses, especially salinity that adversely affects more than 20% of the cultivated land. 

Control of mRNA stability in response to abiotic stress

Fine regulation of gene expression is required for normal growth and development, as well as for stress adaptation.  Although research has focused on regulation that is exerted at the transcriptional level, post-transcriptional control of gene expression is now emerging as a pivotal check point.  mRNA stability is one of the major post-transcriptional regulation mechanisms.   The components of the mRNA decay machinery, especially those involved in signal transduction pathways that convert environmental stimuli into changes in mRNA stability, remain largely unknown.  A very interesting phenomena observed from my previous findings is that the SOS1 transcript level in transgenic plants overexpressing SOS1 is substantially up-regulated by NaCl treatments (Shi et al., 2003), suggesting that a post-transcriptional regulation mechanism might be involved in controlling the stability of SOS1 transcripts.  Research will be performed to identify: 1. the core cis-elements in the 5’ coding sequence of the SOS1 transcript that are responsible for mRNA instability and NaCl-induced stability, 2. the trans-acting proteins that modulate SOS1 mRNA instability and stability using in vitro and in vivo interaction techniques, and 3. components of the signaling pathway that control SOS1 mRNA stability by screening for mutants that alter SOS1 mRNA transcript abundance.

Role of AtHKT1 on ion homeostasis under salt stress

The Arabidopsis thaliana HKT1 (AtHKT1)  controls Na⁺ transport in planta since loss-of-function mutations suppress the Na⁺ sensitive phenotype of sos3, sos2 and sos1 (salt-overly-sensitive) mutant seedlings by reducing Na⁺ accumulation. A significant new discovery is that hkt1 mutations also suppress the K⁺-deficient phenotype of sos seedlings and facilitate the maintenance of intracellular K⁺ levels in environments with excess NaCl. The goal of our research is to understand how Na⁺ and K⁺ acquisition and homeostasis are interrelated and coordinately controlled by using AtHKT1 molecular genetic resources. Specific aims of our research are to: 1. Establish the cellular role of AtHKT1 in Na⁺ and K⁺ acquisition and the role of AtHKT1 in Na⁺ and K⁺ uptake and transport from root to shoot in whole plant context using our loss- and gain-of-function genetic resources, 2. Identify AtHKT1 regulators by genetic, molecular and biochemical approaches.

 Chromatin Remodeling and Stress Responses

The organization of chromatin is a fundamental transcriptional control mechanism in eukaryotic cells.  Chromatin remodeling mediated by modification of epigenetic components in selected DNA can either activate or suppress the expression of embedded genes.  As components of the nucleosome, histones and their modification by acetylation and deacetylation are elucidated to regulate gene expression in eukaryotic organisms.  We recently isolated a mutant showing enhanced expression of stress and ABA responsive genes, and phenotypes of sensitivity to freezing and delayed flowering, suggesting that this gene is a negative regulator of stress and ABA signaling.  Molecular approaches revealed a T-DNA insertion in a gene encoding a WD-repeat protein that is localized in nucleus and can physically bind to H2B and H4.  Together with its high similarity to a human protein that is a component of a protein complex involving in chromatin remodeling, it suggests that this protein might be involved in chromatin remodeling through histone acetylation/deacetylation to regulate gene expression.  Research will be conducted to dissect a putative nuclear repressor complex in Arabidopsis and to elucidate the mechanism of repressive chromatin formation in response to abiotic stresses.