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Abscisic Acid (ABA) Abscisic Acid (ABA) © 2015 American Society of Plant Biologists Seed quality ABSCISIC ACID (ABA) Dormancy Germination controls many plant processes including stress responses, development and reproduction Abscisic Acid Development Biotic stress response Gene expression Stomatal aperture Stress tolerance Adapted with permission from RIKEN © 2015 American Society of Plant Biologists Lecture Outline • ABA biosynthesis, homeostasis and transport • ABA receptors • Downstream signaling • Whole-plant responses • Guard cell responses • Root developmental responses • Vegetative desiccation responses • Seed desiccation and dormancy • Biotic stress responses © 2015 American Society of Plant Biologists Biosynthesis, homeostasis and transport ABA levels increase during stress but decrease when stress is relieved Jan Zeevaart (1930-2009) was a major contributor to our understanding of ABA synthesis and homeostasis. Image courtesy of Michigan State University-Department of Energy Plant Research Lab; Zeevaart, J.A.D. (1980). Changes in the levels of abscisic acid and its metabolites in excised leaf blades of Xanthium strumarium during and after water stress. Plant Physiol. 66: 672-678. © 2015 American Society of Plant Biologists ABA is synthesized in the plastid and cytoplasm and is derived from zeaxanthin, a plant pigment Zeaxanthin Zeaxanthin is abundant in green tissues but can be ABA ABA2 limiting for ABA synthesis in roots Reprinted from Nambara, E., and Marion-Pol, A. (2003) ABA action and interactions in seeds. Trends Plant Sci. 8: 213-217 with permission from Elsevier. © 2015 American Society of Plant Biologists Zeaxanthin epoxidase (ZEP) converts zeaxanthin to violaxanthin Zeaxanthin Antheraxanthin All trans-Violaxanthin Schwartz, S.H., Qin, X., and Zeevaart, J.A.D. (2003). Elucidation of the indirect pathway of abscisic acid biosynthesis by mutants, genes, and enzymes. Plant Physiol. 131: 1591-1601. © 2015 American Society of Plant Biologists ZEP mutants are ABA deficient and lose water rapidly Wild-type tobacco aba2 mutant Closed stomata Open stomata Leaf water content Marin, E., Nussaume, L., Quesada, A., Gonneau, M., Sotta, B., Hugueney, P., Frey, A., and Marion-Poll, A. (1996). Molecular identification of zeaxanthin epoxidase of Nicotiana plumbaginifolia, a gene involved in abscisic acid biosynthesis and corresponding to the ABA locus of Arabidopsis thaliana.EMBO J 15: 2331 – 2342. © 2015 American Society of Plant Biologists All-trans-violaxanthin rearranges to form 9-cis-epoxycarotenoids 9-cis-epoxycarotenoids Han, S.-Y., Kitahata, N., Sekimata, K., Saito, T., Kobayashi, M., Nakashima, K., Yamaguchi-Shinozaki, K., Shinozaki, K., Yoshida, S., and Asami, T. (2004). A novel inhibitor of 9-cis-epoxycarotenoid dioxygenase in abscisic acid biosynthesis in higher plants. Plant Physiol. 135: 1574-1582. © 2015 American Society of Plant Biologists NCED cleaves 9-cis-epoxycarotenoids to produce xanthoxin NCED is 9-cis- epoxycarotenoid dioxygenase xanthoxin © 2015 American Society of Plant Biologists The first NCED gene was identified from the maize vp14 mutant Leaves from vp14 plants lose water more rapidly than wild- type leaves because of reduced levels of ABA vp14 Wild-type Tan, B.C., Schwartz, S.H., Zeevaart, J.A.D., and McCarty, D.R. (1997). Genetic control of abscisic acid biosynthesis in maize. Proc. Natl. Acad. Sci. USA 94: 12235-12240. © 2015 American Society of Plant Biologists The VP14 protein has NCED activity in vitro Thin-layer chromatography showing cleavage VP14/ of 9-cis-epoxycarotenoids by VP14 NCED Xanthoxin VP14 9cV or 9cN By product From Schwartz, S.H., Tan, B.C., Gage, D.A., Zeevaart, J.A.D., and McCarty, D.R. (1997). Specific oxidative cleavage of carotenoids by VP14 of maize. Science 276: 1872-1874 reprinted with permission from AAAS. © 2015 American Society of Plant Biologists NCEDs are part of a large family, but only some are involved in ABA synthesis Cluster of NCED genes thought to be involved in ABA synthesis. Some are primarily expressed in seeds, and others in vegetative tissues Schwartz, S.H., Qin, X., and Zeevaart, J.A.D. (2003). Elucidation of the indirect pathway of abscisic acid biosynthesis by mutants, genes, and enzymes. Plant Physiol. 131: 1591-1601. © 2015 American Society of Plant Biologists NCED genes are induced by drought stress and during seed maturation Increased mRNA levels are detected within 30 minutes of leaf detachment During seed Days maturation NCED after pollination expression levels increase and then decrease Audran, C., Borel, C., Frey, A., Sotta, B., Meyer, C., Simonneau, T., and Marion-Poll, A. (1998). Expression studies of the zeaxanthin epoxidase gene in Nicotiana plumbaginifolia. Plant Physiol. 118: 1021-1028; Qin, X., and Zeevaart, J.A.D. (1999). The 9-cis-epoxycarotenoid cleavage reaction is the key regulatory step of abscisic acid biosynthesis in water-stressed bean. Proc. Natl. Acad. Sci. USA 96: 15354-15361. © 2015 American Society of Plant Biologists Increased NCED correlates with increased ABA synthesis Control vector PvNCED1 Tobacco plants transformed with an inducible Phaseolis vulgaris NCED gene show increased ABA levels, enhanced drought tolerance and increased seed dormancy Collectively these studies show that NCED expression is highly correlated with ABA levels and a key regulatory event in ABA synthesis Qin, X., and Zeevaart, J.A.D. (2002). Overexpression of a 9-cis-epoxycarotenoid dioxygenase gene in Nicotiana plumbaginifolia increases abscisic acid and phaseic acid levels and enhances drought tolerance. Plant Physiol. 128: 544-551. © 2015 American Society of Plant Biologists Conversion of xanthoxin to ABA requires two enzymes WT aao3 mutants aba2 are wilty WT aao3 aba2 mutants germinate under inappropriate conditions Gonzalez-Guzman, M., et al. (2002). The short-chain alcohol dehydrogenase ABA2 catalyzes the conversion of santhoxin to abscisic aldehyde. Plant Cell 14: 1833-1846. Schwartz, S.H., Qin, X., and Zeevaart, J.A.D. (2003). Elucidation of the indirect pathway of abscisic acid biosynthesis by mutants, genes, and enzymes. Plant Physiol. 131: 1591-1601. Seo, M., et al. (2000). The Arabidopsis aldehyde oxidase 3 (AAO3) gene product catalyzes the final step in abscisic acid biosynthesis in leaves. Proc. Nalt. Acad. Sci. USA 97: 12908-12913. © 2015 American Society of Plant Biologists ABA levels are also controlled by inactivation pathways Rehydration Developmental signals [ABA] -Glc © 2015 American Society of Plant Biologists Rehydration of vegetative tissues causes ABA levels to drop ABA Xanthium ABA accumulates eliminated strumarium Leaf detached Rehydration to initiation by immersion Rehydration drying at time in water ZERO ABA Krochko, J.E., Abrams, G.D., Loewen, M.K., Abrams, S.R., and Cutler, A.J. (1998). (+)-Abscisic Acid 8'-Hydroxylase Is a Cytochrome P450 Monooxygenase. Plant Physiol. 118: 849-860. Zeevaart, J.A.D. (1980). Changes in the levels of abscisic acid and its metabolites in excised leaf blades of Xanthium strumarium during and after water stress. Plant Physiol. 66: 672-678. Charles T. Bryson, USDA Agricultural Research Service, Bugwood.org © 2015 American Society of Plant Biologists Rehydration of vegetative tissues causes ABA levels to drop ABA ABA converted Xanthium accumulates strumarium to phaseic acid Phaseic Acid Leaf detached Rehydration to initiation by immersion Rehydration drying at time in water ZERO ABA Krochko, J.E., Abrams, G.D., Loewen, M.K., Abrams, S.R., and Cutler, A.J. (1998). (+)-Abscisic Acid 8'-Hydroxylase Is a Cytochrome P450 Monooxygenase. Plant Physiol. 118: 849-860. Zeevaart, J.A.D. (1980). Changes in the levels of abscisic acid and its metabolites in excised leaf blades of Xanthium strumarium during and after water stress. Plant Physiol. 66: 672-678. Charles T. Bryson, USDA Agricultural Research Service, Bugwood.org © 2015 American Society of Plant Biologists ABA is deactivated by ABA-8′- hydroxylase, encoded by CYP707A Low humidity High humidity CYP707A genes are upregulated upon transfer to high humidity Okamoto, M., Tanaka, Y., Abrams, S.R., Kamiya, Y., Seki, M., and Nambara, E. (2009). High humidity induces abscisic acid 8'-hydroxylase in stomata and vasculature to regulate local and systemic abscisic acid responses in Arabidopsis. Plant Physiol. 149: 825-834. © 2015 American Society of Plant Biologists Drought tolerance by chemical inhibition of 8′-hydroxylase action Inhibitors of P450 enzymes can slow the degradation of ABA by ABA 8′- hydroxylase Reprinted from Kitahata, N., Saito, S., Miyazawa, Y., Umezawa, T., Shimada, Y., Min, Y.K., Mizutani, M., Hirai, N., Shinozaki, K., Yoshida, S., and Asami, T. (2005). Chemical regulation of abscisic acid catabolism in plants by cytochrome P450 inhibitors. Bioorg. Med. Chem. 13: 4491-4498 and Todoroki, Y., Kobayashi, K., Yoneyama, H., Hiramatsu, S., Jin, M.-H., Watanabe, B., Mizutani, M., and Hirai, N. (2008). Structure-activity relationship of uniconazole, a potent inhibitor of ABA 8'-hydroxylase, with a focus on hydrophilic functional groups and conformation. Bioorg. Med. Chem. 16: 3141-3152.with permission from Elsevier © 2015 American Society of Plant Biologists Uniconazole inhibits P450 enzymes, but non-specifically P450 inhibitors are often non- specific. Uniconazole inhibits ABA inactivation AND gibberellin (GA) synthesis, causing growth reduction Reprinted from Kitahata, N., Saito, S., Miyazawa, Y., Umezawa, T., Shimada, Y., Min, Y.K., Mizutani, M., Hirai, N., Shinozaki, K., Yoshida, S., and Asami, T. (2005). Chemical regulation of abscisic acid catabolism
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