Jasmonate-induced oxygenases are novel players in immune suppression acting as jasmonic acid hydroxylases
L. CAARLS (1), J. Elberse (1), M. Awwanah (1), N. Ludwig (1), T. Zeilmaker (1), M. de Vries (2), R. Schuurink (2), G. Van den Ackerveken (1) (1) Utrecht University, Netherlands; (2) University of Amsterdam, Netherlands

The plant hormone jasmonic acid (JA) plays a vital role in defense against necrotrophic pathogens and insect herbivores. Although much is known about biosynthesis of JA and how its bioactive form JA-isoleucine activates the expression of defense genes, knowledge on JA metabolism is incomplete. In particular, it is unknown what enzyme hydroxylates JA into 12-OH-JA, an inactive form of JA that accumulates after wounding and pathogen attack. Here, we report the identification of a clade of four 2-oxoglutarate/Fe(II)-dependent oxygenases in Arabidopsis that is involved in JA hydroxylation. As the expression of the encoding genes is induced by JA we named them JASMONATE-INDUCED OXYGENASEs (JOXs). Metabolite analysis showed that a quadruple mutant of the four genes (jox4x) over-accumulated JA and was impaired in its ability to hydroxylate JA into 12-OH-JA. In contrast, plants overexpressing JOX1 accumulated more 12-OH-JA than wild-type plants when JA was supplied exogenously. The jox4x mutant showed higher expression of JA-related defense genes and increased resistance to the necrotrophic fungus Botrytis cinerea and the insect herbivore Mamestra brassicae. Other JA-related phenotypes, e.g. inhibition of root and shoot growth, were also observed. By identifying the enzymes responsible for hydroxylation of JA, our research reveals a missing step in JA metabolism. Moreover, we show that through inactivation of JA, these enzymes negatively regulate defense. 

Abstract Number: P16-442
Session Type: Poster