Water Stress-Induced Genes inArabidopsis thaliana

Abstract

Plants respond to conditions of severe environmental changes or stresses, such as dehydration, low temperature, high-salinity with a number of physiological and developmental changes. We have isolated more than thirty genes that respond to dehydration stresses at transcriptional level. In the present study, we will report the expression and function of differentArabidopsis genes involved in the kinase cascade and in the proline biosynthesis. MAP kinases play key roles in the signalling pathway activated by growth factors and in stress response in animals. The mRNA levels of three protein kinases, ATMEKK1 (MAP kinase kinase kinase), ATMPK3 (MAP kinase) and ATPK19 (ribosomal S6 kinase), increased markedly and simultaneously in response to touch, cold and salinity stresses. These results suggest that MAP kinase cascades, which are thought to respond to a variety of extracellular signals, are regulated not only at the post-translational level but also at the transcriptional level in plants. It is also suggested that MAP kinase cascades in plants may function in transducing signals under environmental stresses. Proline is thought to be a compatible osmolyte like glycine betaine, which plays a role in counteracting the effects of osmotic stress in plants. We have isolated two cDNAs fromArabidopsis (cAtPSCS andcAtPSCR) encoding P5CS (Δ¹-pyrroline-5-carboxylate synthetase) and P5CR (Δ¹-pyrroline-5-carboxylate reductase) which play key roles in the biosynthesis of proline in plants under water stress. Northern blot analysis revealed that theAtP5CS gene was induced by dehydration, high salt and treatment with ABA. Moreover, a simultaneous accumulation of proline was observed as a result of these treatments ofArabidopsis plants. By contrast, theAtPSCR gene was not induced to a significant extent by dehydration or high-salt stress. These observations suggest that theAtP5CS gene plays a principal role in the biosynthesis of proline inArabidopsis under osmotic stress.