Plant & Animal Genome IX Conference

Poster: Sequencing & EST
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GENE DISCOVERY AND TRANSCRIPT PROFILING OF SALINITY STRESS RESPONSES BY EXPRESSED SEQUENCE TAG (EST) ANALYSIS IN THE COMMON ICE PLANT, MESEMBRYANTHEMUM CRYSTALLINUM.

¹ Department of Biochemistry and Molecular Biology, Saitama University Urawa 338-8570

² Department of Biochemistry, University of Nevada, Reno NV 89557-0014

The common ice plant, Mesembryanthemum crystallinum, has emerged as a useful model for understanding plant abiotic stress responses and Crassulacean acid metabolism (CAM), a photosynthetic adaptation to water limitation. This extremely stress tolerant, halophytic, inducible CAM species has a relatively short life cycle, a small genome (390 Mb or 2.5 times larger than Arabidopsis thaliana), and a growing collection of morphological and biochemical mutants available. In spite of these advantages, relatively few genes have been characterized from this species compared with other higher plant models. Therefore, we have conducted large-scale expressed sequence tag (EST) analysis of randomly selected cDNAs derived from leaf tissues of well-watered and salinity-stressed (0.4 M NaCl for 30 and 48 h) plants. At present, about 12,000 ESTs have been obtained from various tissues representing more than 6,000 non-redundant sequences. Abundance of transcripts encoding light harvesting and photosystem complexes and C₃ photosynthetic enzymes decreased dramatically following salinity stress. In contrast, salt stress brought about pronounced increases in transcripts involved in CAM, disease and/or defense responses, abiotic stress adaptation, proteolysis and ion homeostasis. Moreover, stressed plants contained a higher percentage of ESTs encoding novel and functionally unknown proteins. The rapid discovery of new and unknown ice plant genes related to stress adaptation demonstrates the great utility of EST analysis in unraveling the complex set of adaptive mechanisms contributing to salinity and drought tolerance.