Pf. Straub et al., STRUCTURE AND PROMOTER ANALYSIS OF AN ABA-REGULATED AND STRESS-REGULATED BARLEY GENE, HVA1, Plant molecular biology, 26(2), 1994, pp. 617-630
A single-copy barley gene, HVA1, encoding a class 3 late embryogenesis
-abundant protein, can be induced by either treatment with abscisic ac
id (ABA) or by stress conditions such as drought, cold, heat and salin
ity. We have isolated an HVA1 genomic clone containing about 400 bp of
5'-upstream sequence, a single 109 bp intron, and the full coding seq
uence. Linker scan mutagenesis and transient expression studies were u
sed to test the function of four HVA1 promoter elements conserved in A
BA-responsive genes. Mutations in two of these elements, the C box and
the putative ABRE 1 (ABA-responsive element) containing an ACGT core,
resulted in no significant change in transcription level or ABA induc
tion. In contrast, mutations of the other two elements, putative ABRE
2 and 3 cause the level of transcription to drop to 10-20 % of that ob
tained with the wild-type promoter indicating that the high level of e
xpression of HVA1 is dependent on both pABRE 2 and 3. Interestingly, d
espite their low level of expression, the mutated promoters still gave
more than 20-fold induction in response to ABA treatment. We suggest
that the ABA induction of barley HVA1 gene is governed by a complex co
nsisting of pABRE 2 and 3 working together to regulate the absolute le
vel of expression, and either of these elements or a possible third el
ement may regulate ABA inducibility. Phylogenetic analysis by parsimon
y indicates that the barley HVA1 and wheat pMA2005 sequences share a r
ecent common ancester. These two genes are closely related to the carr
ot Dc3 and cotton D-7 genes with which they share a similar structural
gene organization.