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Metabolic and genomic profiling of transgenic tomato lines expressing inositol polyphosphate 5-phosphatase   Mariya Khodakovskaya¹, Chiu-Yeh Hung¹, Imara Perera¹, Wendy Boss¹, Christopher Brown^1,2 and Heike Winter Sederoff ¹

¹Department of Plant Biology, ²Kenan Institute for Science and Engineering, North Carolina  State University, Raleigh, NC

   Inositol-1,4,5-trisphosphate (InsP₃) is secondary messenger involved in plant signal transduction pathways. Rapid, transient increases in InsP₃ have been demonstrated in plant tissues in response to a variety of environmental stresses. Expression of inositol polyphosphate 5-phosphatase (InsP 5-ptase), an enzyme which hydrolyzes InsP₃, dramatically reduced steady-state levels of InsP₃ in Arabidopsis plants and resulted in a decreased and delayed response to gravity and increased tolerance to drought stress (Perera et al. 2006; and unpublished data). We transformed tomato plants (v. Micro-Tom) with InsP 5-ptase to study the effect of dampened InsP₃ levels in a crop plant. Constitutive expression of InsP 5-ptase decreased InsP₃ levels in leaves and fruits analyzed. Preliminary data indicate correlating increases in ABA levels and dramatically increased tolerance to drought stress. Some transgenic lines exhibited phenotypical and morphological differences in leaf and stem thickness. We are currently analyzing the effects of the transgene expression on global gene expression using Affymetrix Microarrays. We are suggesting that decreasing of InsP₃ levels affect not only plant stress response but also the metabolic profile and nutritional characteristics in the transgenic lines. Using realtime PCR, we found several fold increases in the transcript abundance of chalcone synthase (LECHS1), a key enzyme in the flavonoid biosynthetic pathway, in five independent transgenic tomato lines compared to wild type. Because primary and secondary metabolite levels play important roles in plant stress responses, composition and level of basic metabolite groups should be different in cells expressing genes involved in stress signal transductional pathway. We are integrating genomic and metabolomic data with to understand the mechanism by which InsP₃ metabolism regulates vegetative and generative tissues of transgenic tomato lines.

(Supported by NASA grant NAG2-1566 to CSB and NC Space Grant 526294 to MVK)