Osmotin gene expression in response to hormonal and environmental signals
Abstract
In response to adaptation to NaCl, cultured cells of Nicotiana tabacum L. var. Wisconsin 38 synthesize a major 26 kD protein which has been named osmotin due to its induction by low water potentials. This protein is also a member of the PR-5 (pathogenesis related) gene family. cDNA and genomic clones encoding this protein were isolated for use in experiments to study the regulation of this gene. Osmotin mRNA accumulates in cells in response to exogenously applied ABA and adaptation to NaCl but not to NaCl shock treatments. Nuclear run-on transcription studies indicated that ABA exerts its effect through an increase in transcription rate. To study the effects of hormonal and environmental signals on osmotin promoter activity in plants, an osmotin promoter/$\beta$-glucuronidase gene fusion was constructed and introduced into tobacco via Agrobacterium-mediated transformation. Similar to the tissue expression pattern for other basic PR genes, root tissues contained the highest levels of GUS activity. GUS activity was highly inducible in four day old R1 seedlings by treatment with ABA. Osmotin promoter activity showed a linear response to ABA when compared to the log of hormone concentration. Promoter activity increased within one hour and rose continuously for 24 hours. The sensitivity to ABA decreased with the age of the seedlings in both root and shoot tissues. Ethylene induced promoter activity irrespective of age of the seedlings. Wounding induced promoter activity and the effect is mediated through ethylene. NaCl shock treatments induced promoter activity in plants and the effect is apparently mediated through ABA. Expression of osmotin genes in the diploid parents of tobacco, N. sylvestris and N. tomentosiformis was also studied. Protein accumulates to high levels in the roots of both parents. Steady state levels of mRNA are higher in N. sylvestris than in N. tomentosiformis while protein levels are equal, potentially indicating post-transcriptional regulation of the gene(s). In both parents, ABA and ethylene treatments induced mRNA accumulation. Studies were initiated in a tobacco cell suspension culture system to determine if osmotin has a role in adaptation to NaCl. Strategies based on overexpression driven by the CaMV 35S promoter and anti-sense RNA inhibition were employed.
Degree
Ph.D.
Advisors
Bressan, Purdue University.
Subject Area
Molecular biology
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