Downstream DNA sequences are required to modulate Pvlea-18 gene expressionin response to dehydration

We have previously shown that mRNA and protein encoded by the Pvlea-18 gene from Phaseolus vulgaris L., a member of a new family of late embryogenesis -abundant (LEA) proteins, accumulate in dark-grown bean seedlings not only in response to water deficit but also during optimal irrigation. In this wo rk, we studied Pvlea-18 gene transcriptional regulation by using transgenic Arabidopsis thaliana plants containing a chimeric gene consisting of the P vlea-18 promoter region and the 3'-nos terminator fused to the GUS gene-cod ing region. We demonstrate that the chimeric gene is active during Arabidop sis normal development under well-irrigated conditions, and that it is furt her induced in response to ABA and dehydration treatments. Replacing the 3' -nos terminator with the Pvlea-18 3' region led to an additional increase i n expression during development and in response to dehydration, but not in response to exogenous ABA. These results reveal an enhancer effect of the P vlea-18 3' region, which showed to be higher specifically under dehydration . The small decrease in Pvlea-18 promoter expression observed when transgen ic plants treated with fluridone (an ABA biosynthesis inhibitor) were subje cted to dehydration suggests that the Pvlea-18 gene dehydration response is predominantly ABA-independent. Finally, we present evidence indicating tha t Pvlea-18 gene expression is negatively regulated during etiolated growth, particularly in roots, in contrast to the expression pattern observed duri ng normal development.