Gene Expression during Dehydration Stress in the Resurrection Plant Craterostigma plantagineum

Abstract

The resurrection plant Craterostigma plantagineum is being used as an experimental model system to dissect pathways leading to desiccation tolerance. This plant can recover from severe desiccation within 24 h of contact with water. During drying or ABA treatment novel gene products accumulate rapidly in leaves and other tissues. It is proposed that these gene products contribute to the protection of cellular structures during dehydration. It has been a major goal to isolate genes and determine parameters which regulate the expression of the responsive genes. One approach was to characterize promoters. Three promoters from different lea type genes and three promoters from genes encoding inducible enzymes of the carbohydrate metabolism have been analyzed for their responsiveness to drought and ABA in transient assays and in transgenic plants. The promoter activities in transgenic plants suggest differences in the mode of the regulatory pathways and point to at least two transduction pathways. Evidence has been accumulated that the activation of at least one promoter in vegetative tissues depends on a gene product related to the Arabidopsis abi3-gene. In gel shift mobility assays it was shown that nuclear proteins from ABA treated callus and leaves specifically bind sequence elements in the promoter region. Other environmental factors such as light interact with desiccation stress and modulate the expression level of the proteins involving post-transcriptional and post-translational mechanisms. To dissect events in this signal transduction chain, two other experimental approaches have been initiated. A T-DNA based tagging experiment was carried out in order to obtain positive mutations over- expressing gene products downstream of the ABA signal. One such mutant has been obtained and has been molecularly characterized. A subtractive and differential screening is being used to isolate cDNA clones which encode transcripts expressed during the very early events of dehydration.