The stress- and abscisic acid-induced barley gene HVA22: developmental regulation and homologues in diverse organisms

Abscisic acid (ABA) induces the expression of a battery of genes in mediati ng plant responses to environmental stresses. Here we report one of the ear ly ABA-inducible genes in barley (Hordeum vulgare L.), HVA22, which shares little homology with other ABA-responsive genes such as LEA (late embryogen esis-abundant) and RAB (responsive to ABA) genes. In grains, the expression of HVA22 gene appears to be correlated with the dormancy status. The level of HVA22 mRNA increases during grain development, and declines to an undet ectable level within 12 h after imbibition of non-dormant grains. In contra st, the HVA22 mRNA level remains high in dormant grains even after five day s of imbibition. Treatment of dormant grains with gibberellin (GA) effectiv ely breaks dormancy with a concomitant decline of the level of HVA22 mRNA. The expression of HVA22 appears to be tissue-specific with the level of its mRNA readily detectable in aleurone layers and embryos, yet undetectable i n the starchy endosperm. The expression of HVA22 in vegetative tissues can be induced by ABA and environmental stresses, such as cold and drought. App arent homologues of this barley gene are found in phylogenetically divergen t eukaryotic organisms, including cereals, Arabidopsis, Caenorhabitis elega ns, man, mouse and yeast, but not in any prokaryotes. Interestingly, simila r to barley HVA22, the yeast homologue is also stress-inducible. These obse rvations suggest that the HVA22 and its homologues encode a highly conserve d stress-inducible protein which may play an important role in protecting c ells from damage under stress conditions in many eukaryotic organisms.