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PLANTS INTERACTING WITH OTHER ORGANISMS

Evidence for Abscisic Acid Biosynthesis in Cuscuta reflexa, a Parasitic Plant Lacking Neoxanthin^1,[W],[OA]

Department of Energy Plant Research Laboratory (X.Q., S.H.Y., A.C.K., S.H.S., J.A.D.Z.) and Department of Plant Biology (J.A.D.Z.), Michigan State University, East Lansing, Michigan 48824–1312

Abscisic acid (ABA) is a plant hormone found in all higher plants; it plays an important role in seed dormancy, embryo development, and adaptation to environmental stresses, most notably drought. The regulatory step in ABA synthesis is the cleavage reaction of a 9-cis-epoxy-carotenoid catalyzed by the 9-cis-epoxy-carotenoid dioxygenases (NCEDs). The parasitic angiosperm Cuscuta reflexa lacks neoxanthin, one of the common precursors of ABA in all higher plants. Thus, is C. reflexa capable of synthesizing ABA, or does it acquire ABA from its host plants? Stem tips of C. reflexa were cultured in vitro and found to accumulate ABA in the absence of host plants. This demonstrates that this parasitic plant is capable of synthesizing ABA. Dehydration of detached stem tips caused a big rise in ABA content. During dehydration, ¹⁸O was incorporated into ABA from ¹⁸O₂, indicating that ABA was synthesized de novo in C. reflexa. Two NCED genes, CrNCED1 and CrNCED2, were cloned from C. reflexa. Expression of CrNCEDs was up-regulated significantly by dehydration. In vitro enzyme assays with recombinant CrNCED1 protein showed that the protein is able to cleave both 9-cis-violaxanthin and 9'-cis-neoxanthin to give xanthoxin. Thus, despite the absence of neoxanthin in C. reflexa, the biochemical activity of CrNCED1 is similar to that of NCEDs from other higher plants. These results provide evidence for conservation of the ABA biosynthesis pathway among members of the plant kingdom.

² These authors contributed equally to the article.

³ Present address: Department of Plant Sciences, University of California Davis, CA 95616.

⁴ Present address: Department of Biological Science, Institute of Bioscience and Biotechnology, Science Campus, Myongji University San 38–2, Namdong, Cheoin-Gu, Yongin, Gyeonggi, 449–728, Korea.

⁵ Present address: Room B4325, VA Medical Center, 4646 John R, Detroit, MI 48201.

⁶ Present address: Monsanto Company, Calgene Campus, Davis, CA 95616.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Jan A.D. Zeevaart (zeevaart{at}msu.edu).

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.116749

^* Corresponding author; e-mail zeevaart{at}msu.edu.

Received January 25, 2008; accepted April 23, 2008; published April 25, 2008.