Poster: Hormones

Abs # 576: The site of ABA biosynthesis and the ABA transport in Arabidopsis

Presenter:	Koshiba, Tomokazu , koshiba-tomokazu@c.metro-u.ac.jp
Authors	Koshiba, Tomokazu  (A)   Koiwai, Hanae  (A)   Ikegami, Keiichi  (A)
Affiliations:	(A): Tokyo Metropolitan University
Web Site:	http://www.comp.metro-u.ac.jp/~koshiba/

Abscisic acid (ABA) is a plant hormone that regulates many aspects of plant growth and development, including tolerance to a variety of environmental stresses. Since many of these physiological processes correlate with endogenous ABA levels, the regulation of ABA biosynthesis is one of the key elements facilitating the elucidation of the molecular mechanisms of ABA actions. Recent studies based on the cloning of genes encoding enzymes responsible for ABA biosynthesis revealed an overview of the main ABA biosynthetic pathway. However, details of the ABA biosynthesis site(s) and ABA transport are still unknown. Our recent works dealing with the Arabidopsis aao3 mutant gene have suggested the presence of more complex regulations of ABA biosynthesis and transportation of ABA and/or ABA precursor in plants. (1) AAO3, a member of the aldehyde oxidase family, catalyzes the oxidation of abscisic aldehyde to form ABA. (2) A rapid ABA biosynthesis in response to drought stress takes place mainly in leaves, and AAO3 plays a critical role in the regulation. (3) ABA synthesized in leaves during drought stress is transported to roots. (4) Expression of AAO3-GFP fusion protein driven by AAO3 promoter is observed along with leaf veins and in root tips. These results suggest the possibility for inter-organ and inter-cellular mobilization of ABA precursors and/or ABA to the target sites. A possible source of ABA for rapid stomatal closure in response to water stress will also be discussed in this session.