Signal transduction pathways involved in the regulation of plant defense gene expression by hormonal and environmental inducers
Abstract
Osmotin gene expression can be regulated by at least eight hormonal and environmental inducers. The induction of osmotin gene by salt and wounding may be through the combination of different hormone pathways. Different hormones activate osmotin gene expression by separate signal transduction pathways. Combinations of ethylene and methyl jasmonate (E/JA) can synergistically induce two defense genes, PR1 and PR5 (osmotin). E/JA causes a synergistic induction of PR-1 and osmotin (PR-5) mRNA accumulation in tobacco seedlings. E/JA also synergistically activated the osmotin promoter fused to a GUS marker gene in a tissue specific manner. The E/JA responsiveness of the osmotin promoter is localized on a $-$248/+45 fragment that exhibits responsiveness to several other inducers. Although no apparent E/JA induced qualitative or quantitative change in DNA-binding proteins were detected in situations where the promoter is synergistically induced, this induction did require protein synthesis. E/JA also resulted in osmotin protein accumulation to levels similar to those induced by osmotic stress. Of the several known inducers of the osmotin gene including salicylic acid (SA), fungal infection is the only other condition known to cause substantial osmotin protein accumulation in Wisconsin 38, a tobacco genotype that does not respond hypersensitively to tobacco mosaic virus. Based on the ability of the protein kinase C inhibitor, H7, to block ethylene induction of PR-1 mRNA accumulation, and its inability to block osmotin mRNA induction by ethylene, these two PR gene groups appear to have at least partially separate transduction pathways. Stimulation of osmotin mRNA accumulation by okadaic acid indicates that another protein kinase system is involved in regulation of the osmotin gene. SA, which is known to induce pathogen resistance in tobacco, cannot induce the osmotin gene as much as E/JA nor can it induce PR-1 as much as SA and JA combined.
Degree
Ph.D.
Advisors
Bressan, Purdue University.
Subject Area
Botany|Molecular biology
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