Hormone and stress-regulated gene expression in plants



-Amylase in action. Scanning EM of starch granules form barley seed being digested (holes in surface) by -amylase which is regulated by plant hormones, gibberellins and abscisic acid

"ABA Response Complexex (ABRCs): promoter switches which are necessary and sufficient for ABA induced gene expression"

Abscisic Acid induced genes and drought resistance.
The two tobacco plants shown are genetically identical except that the plant on the left has been engineered to overexpress a gene, HVA1, induced by abscisic acid or stress conditions. Overexpression of this gene allows the transgenic plant to withstand drought better than the control plant on the right, which is clearly wilted. Water was withheld from both plants on the same day and the moisture content of the soil is essentially identical for the two plants shown.

We are interested in the mechanisms of developmental transition from embryogenesis to seed germination, a process governed by two phytohormones, gibberellins (GA) and abscisic acid (ABA). Since plant embryos are very resistant to environmental stresses such as drought and cold, we also study the role of stress-induced proteins in mediating stress tolerance in plants.

1) Hormonal control of gene expression in the aleurone cells of cereal grains.

In this project we study the effect of GA and ABA on the expression of genes encoding alpha-amylases, proteases and nucleases in germinating cereal grains. We follow both biochemical and genetic approaches to investigate the structure and function of these genes and their protein products. We are currently investigating transcription factors, such as a Myb type DNA binding protein called GAMYB and a suppressor, HRT, which interact with specific regions in the alpha-amylase and protease gene promoters. We are also interested in elucidating the role of protein phosphatase 2C and a ser/thr protein kinase, PKABA1, on mediating the ABA-regulated gene expression. Future work includes the study of interactions among these factors and how hormones affect their levels and/or activities. The stress/ABA up-regulation of genes encoding late embryogenesis abundant (LEA) proteins has also been a subject of intensive study. We have determined that the promoter complex necessary and sufficient for ABA up-regulation consists of an ACGT box (G-box) and a coupling element. We are currently cloning the transcription factors that specifically interact with these stress/ABA responsive promoter elements. We will study the effect of ABA treatment on the sub-cellular distribution of these transcription factors. We also plan to use genetic mutants with altered hormone sensitivities to further elucidate the action of these hormones.

2) Regulation and function of stress-induced genes.

We are particularly interested in the function of drought, salinity and cold stress induced proteins in cereals and Arabidopsis. One of these proteins, HVA1, contains long stretches of amphipathic alpha-helical structure, and its over- expression in transgenic plants leads to elevated levels of stress tolerance. Another stress/ABA-induced protein, HVA22, has apparent homologs in many diverse eukaryotes, but not in any prokaryotes. Studies of the HVA22 homolog in yeast suggest that this protein be involved in vesicular transport that may be essential for modifications of the structure and function of plasma membrane. We are further investigating the function of these two stress/ABA induced protein following a multidisciplinary approach employing tools in cell biology, biochemistry and genetics. A patent on the use of HVA1 to generate stress tolerant plants has recently been approved. Efforts are underway to establish collaborations with industrial interests in further developing this technology.

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