How Plants Use Sugar to Cope with Stress

Abstract

Cheng et al. have developed an intriguing model whereby glucose may modify plant growth and development in response to prevailing environmental conditions by regulating biosynthesis of the plant hormone abscisic acid (ABA). Glucose and other sugars play a key role in plant growth and development by modulating such processes as germination, seedling development, and senescence. Glucose regulates intrinsic developmental programs by mechanisms that remain unclear; phenotypic and genetic analyses, however, have implicated signaling pathways involving two plant stress hormones with growth-inhibitory activity, ABA and ethylene, in the glucose response. Using genetic crosses of glucose-insensitive and ABA-deficient Arabidopsis mutants, together with map-based cloning and complementation analysis, Cheng et al. identified a gene, ABA2/GIN1, implicated in both glucose-insensitive and ABA-deficient phenotypes. Sequence analysis indicated that ABA2/GIN1 encodes a unique member of a superfamily of short-chain dehydrogenase/reductases (SDR1) found in plants, animals, and bacteria. Biochemical analyses using purified SDR1 indicated that ABA2/GIN1 was essential for the major pathway for ABA biosynthesis. The authors delineated a complex interrelationship among glucose, ABA, and ethylene: glucose activates the expression of ABA2/GIN1 and other genes involved in ABA biosynthesis synergistically with ABA, and antagonizes ethylene pathways in part through ABA biosynthesis. Phenotypic analysis of mutant plants suggested that ABA may promote growth under relatively stress-free conditions and may inhibit growth during severe environmental stress. Also, that glucose concentration may serve as a reporter of environmental conditions. ABA2/GIN1 localization, determined both by Northern analysis and with reporter genes containing the ABA2/GIN1 promoter, was spatially and temporally restricted and distinct from both ABA target sites and the location of other genes involved in ABA biosynthesis, which suggests dynamic transport of ABA or its precursors.W. H. Cheng, A. Endo, L. Zhou, J. Penney, H.-C. Chen, A. Arroyo, P. Leon, E. Nambara, T. Asami, M. Seo, T. Koshiba, J. Sheen, A unique short-chain dehydrogenase/reductase in Arabidopsis glucose signaling and abscisic acid biosynthesis and functions. Plant Cell 14, 2723-2743 (2002). [Abstract] [Full Text]