CLONING OF CDNAS FOR GENES THAT ARE EARLY-RESPONSIVE TO DEHYDRATION STRESS (ERDS) IN ARABIDOPSIS-THALIANA L - IDENTIFICATION OF 3 ERDS AS HSP COGNATE GENES

In Arabidopsis thaliana L., accumulation of abscisic acid (ABA) began to increase 2 h after plants had been subjected to dehydration stress and reached maximum levels after 10 h. Differential hybridization was used to isolate 26 Arabidopsis cDNAs with gene expression induced by a 1 h dehydration treatment. The cDNA clones were classified into 16 gr oups based on Southern blot hybridization, and named ERD (early-respon sive to dehydration) clones. Partial sequencing of the cDNA clones rev ealed that three ERDs were identical to those of HSP cognates (Athsp70 -1, Athsp81-2, and ubiquitin extension protein). Dehydration stress st rongly induced the expression of genes for the three ERDs, while appli cation of ABA, which is known to act as a signal transmitter in dehydr ation-stressed plants, did not significantly affect the ERD gene expre ssion. This result suggests that these HSP cognates are preferentially responsive to dehydration stress in A. thaliana, and that signaling p athways for the expression of these genes under conditions of dehydrat ion stress are not mainly mediated by ABA. We also discuss the possibl e functions of these three ERD gene products against dehydration stres s.