Downstream DNA sequences are required to modulate Pvlea-18 gene expression in 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 work, we studied Pvlea-18 gene transcriptional regulation by using transgenic Arabidopsis thaliana plants containing a chimeric gene consisting of the Pvlea-18 promoter region and the 3'-nos terminator fused to the GUS gene-coding region. We demonstrate that the chimeric gene is active during Arabidopsis normal development under well-irrigated conditions, and that it is further induced in response to ABA and dehydration treatments. Replacing the 3'-nos terminator with the Pvlea-18 3' region led to an additional increase in expression during development and in response to dehydration, but not in response to exogenous ABA. These results reveal an enhancer effect of the Pvlea-18 3' region, which showed to be higher specifically under dehydration. The small decrease in Pvlea-18 promoter expression observed when transgenic plants treated with fluridone (an ABA biosynthesis inhibitor) were subjected to dehydration suggests that the Pvlea-18 gene dehydration response is predominantly ABA-independent. Finally, we present evidence indicating that Pvlea-18 gene expression is negatively regulated during etiolated growth, particularly in roots, in contrast to the expression pattern observed during normal development.