Molecular characterization of a mutation affecting abscisic acid biosynthesis and consequently stomatal responses to humidity in an agriculturally important species
McAdam, SAM and Sussmilch, FC and Brodribb, TJ and Ross, JJ, Molecular characterization of a mutation affecting abscisic acid biosynthesis and consequently stomatal responses to humidity in an agriculturally important species, AoB Plants, 7 Article plv091. ISSN 2041-2851 (2015) [Refereed Article]
Mutants deficient in the phytohormone abscisic acid (ABA) have been instrumental in determining not only the biosynthetic
pathway for this hormone, but also its physiological role in land plants. The wilty mutant of Pisum sativum is one of the classic, well-studied ABA deficient mutants; however this mutant remains uncharacterised at a molecular level.
Using a candidate gene approach, we show that the wilty mutation affects the xanthoxin dehydrogenase step in ABA biosynthesis. To date, this step has only been represented by mutants
in the ABA2 gene of Arabidopsis thaliana. Functional ABA biosynthesis appears to be critical for normal stomatal responses to changes in humidity in angiosperms,
with wilty mutant plants having no increase in foliar ABA levels in response to a doubling in vapour pressure deficit and no closure
of stomata. Phylogenetic analysis of the ABA2 gene family from diverse land plants indicates that the evolution of an ABA-biosynthetic-specific short-chain dehydrogenase
(ABA2) evolved in the earliest angiosperms. The relatively recent evolutionary origin of specificity in this step has important
implications for both the evolution of ABA biosynthesis and action in land plants.