Three new osmotic stress-regulated cDNAs identified by differential display polymerase chain reaction in rapeseed leaf discs.

ABSTRACTPlant osmotic stress responses are associated with changes in gene expression. Osmotic stress-regulated genes (OR genes) have been isolated by various approaches such as differential screening of cDNA libraries or by complementation. We have used differential display of mRNA to isolate partial cDNAs corresponding to transcripts differentially expressed in leaf discs from osmotically stressed rapeseed. The cloning and the sequencing of three OR genes (MC12, MC43 and MC24) isolated by this method are reported here. Differences in corresponding mRNA levels during the first hours of stress were confirmed by Northern blot analysis. The deduced amino acid sequence of the MC12 and MC43 clones, for which mRNA accumulation was detected under osmotic stress, shows significant similarities to saccharopine dehydrogenase and linker histone H1-3 genes, respectively. Furthermore these up- regulated genes are induced by ABA. The nucleotide sequence of MC24 shows strong homology with a chloroplast gene (rps12) encoding a ribosomal protein. mRNA hybridization with MC24 led to a multiple banding pattern resulting from maturation of polycistronic precursor transcripts. Levels of different sized transcript hybridizing with MC24 decreased during osmotic stress, suggesting that rps12 chloroplast gene is down-regulated by osmotic stress. Interestingly, up-regulation of a gene encoding an enzyme involved in lysine catabolism suggests that products from this pathway could be of interest for the adaptation of rapeseed leaf explants subjected to osmotic upshock in vitro. This discovery opens new insights into metabolic adjustment mechanisms under stress. [ABSTRACT FROM AUTHOR]