Abscisic acid-dependent and -independent expression of the carrot LEA class gene Dc3 in transgenic tobacco seedlings

Abstract

We studied the expression of three promoter deletion mutants (A218, A599, and A1312) of the Late Embryo Abundant (LEA) class gene Dc3 fused to the reporter gene, B-glucuronidase (GUS) in 14 d old transgenic tobacco seedlings. Seedlings were subjected to one of the following stresses: dehydration, hypoxia, salinity, exogenous ethylene, and exogenous methyl jasmonate (MeJa). GUS activity was quantified fluorometrically, and expression was observed by histochemical staining of the seedlings. An increase in GUS activity was observed in A599 and A1312 mutants in response to dehydration and salinity within 6 h of stress, and at 12 h in response to hypoxia. No increase in endogenous ABA was found in any of the three mutants even after 24 h of hypoxia. ABA-independent increase in GUS activity was observed when endogenous ABA biosynthesis was blocked by fluridone and plants were exposed to 5 [[ ]-' ethylene in air or 100 @M MeJa. No expression was observed in A218 mutant in response to dehydration, salinity, or MeJa. A mild response was observed in response to ethylene or hypoxia. This suggests that the region between-218 and-599 is absolutely necessary for ABA (dehydration and salinity) and MeJa-dependent expression whereas ethylene mediated expression does not require this region of the promoter. This study shows that Dc3, which is an ABA responsive gene, can also be induced by stress signals other than ABA.