Plant Physiology Preview Published on October 21, 2005; 10.1104/pp.105.069054
Received July 28, 2005
Returned for revision July 28, 2005
Accepted September 12, 2005
Suppression of Allene Oxide Cyclase in Hairy Roots of Medicago truncatula Reduces Jasmonate Levels and the Degree of Mycorrhization with Glomus intraradices
Stanislav Isayenkov , Cornelia Mrosk , Irene Stenzel , Dieter Strack , and Bettina Hause *
Department of Secondary Metabolism, Leibniz Institute of Plant Biochemistry, D-06120 Halle (Saale), Germany
Department of Natural Product Biotechnology, Leibniz Institute of Plant Biochemistry, D-06120 Halle (Saale), Germany
* Corresponding author; email: bhause{at}ipb-halle.de.
During the symbiotic interaction between Medicago truncatula and the arbuscular mycorrhizal (AM) fungus Glomus intraradices, an endogenous increase in jasmonic acid (JA) occurs. Two full-length cDNAs coding for the JA-biosynthetic enzyme allene oxide cyclase (AOC) from M. truncatula, designated as MtAOC1 and MtAOC2, were cloned and characterized. The AOC protein was localized in plastids and found to occur constitutively in all vascular tissues of M. truncatula. In leaves and roots, MtAOCs are expressed upon JA application. Enhanced expression was also observed during mycorrhization with G. intraradices. A partial suppression of MtAOC expression was achieved in roots following transformation with Agrobacterium rhizogenes harboring the MtAOC1 cDNA in the antisense direction under control of the cauliflower mosaic virus 35S promoter. In comparison to samples transformed with 35S::uidA, roots with suppressed MtAOC1 expression exhibited lower JA levels and a remarkable delay in the process of colonization with G. intraradices. Both the mycorrhization rate, quantified by fungal rRNA, and the arbuscule formation, analyzed by the expression level of the AM-specific gene MtPT4, were affected. Staining of fungal material in roots with suppressed MtAOC1 revealed a decreased number of arbuscules, but these did not exhibit an altered structure. Our results indicate a crucial role for JA in the establishment of AM symbiosis.
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