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Published on May 6, 2009; 10.1104/pp.109.138420

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Received March 10, 2009
Accepted May 1, 2009

Abscisic acid negatively regulates elicitor-induced synthesis of capsidiol in wild tobacco (Nicotiana plumbaginifolia)

Alexis Samba Mialoundama , Dimitri Heintz , Delphine Debayle , Alain Rahier , Bilal Camara *, and Florence Bouvier

Institut de Biologie Moleculaire des Plantes, Centre National de la Recherche Scientifique and Universite de Strasbourg, 67084 Strasbourg Cedex, France

* Corresponding author; email: Camara{at}ibmp-ulp.u-strasbg.fr.

In the solanaceae, biotic and abiotic elicitors induce de novo synthesis of sesquiterpenoid stress metabolites known as phytoalexins. Because plant hormones play critical roles in the induction of defense-responsive genes, we have explored the effect of abscisic acid (ABA) on the synthesis of capsidiol, the major tobacco sesquiterpenoid phytoalexin using wild-type (WT) Nicotiana plumbaginifolia versus non-allelic mutants Npaba2 and Npaba1 that are deficient in ABA synthesis. Npaba2 and Npaba1 mutants exhibited a two-fold higher synthesis of capsidiol than WT plants when elicited with either cellulase or arachidonic acid, or when infected by Botrytis cinerea. The same trend was observed for the expression of the capsidiol biosynthetic genes, 5-epi-aristolochene synthase (EAS) and 5-epi-aristolochene hydroxylase (EAH). Treatment of WT plants with fluridone, an inhibitor of the upstream ABA pathway, recapitulated the behaviour of Npaba2 and Npaba1mutants, while the application of exogenous ABA reversed the enhanced synthesis of capsidiol in Npaba2 and Npaba1 mutants. Concomitantly with the production of capsidiol, we observed the induction of ABA 8'-hydroxylase (ABAH) in elicited plants. In WT plants, the induction of ABAH coincided with a decrease in ABA content and with the accumulation of ABA catabolic products such as phaseic acid and dihydrophaseic acid, suggesting a negative regulation exerted by ABA on capsidiol synthesis. Collectively, our data indicate that ABA is not required per se for the induction capsidiol synthesis, but is essentially implicated in a stress-response checkpoint to fine-tune the amplification of capsidiol synthesis in challenged plants.






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