Arabidopsis JASMONATE-INDUCED OXYGENASES down-regulate plant immunity by hydroxylation and inactivation of the hormone jasmonic acid

Abstract

The phytohormone jasmonic acid (JA) is vital in plant defense and development. Although biosynthesis of JA and activation of JA-responsive gene expression by the bioactive form JAisoleucine (JA-Ile) have been well-studied, knowledge on JA metabolism is incomplete. In particular, the enzyme that hydroxylates JA to 12-OH-JA, an inactive form of JA that accumulates after wounding and pathogen attack, is unknown. Here, we report the identification of four paralogous 2-oxoglutarate/Fe(II)-dependent oxygenases in Arabidopsis thaliana as JA hydroxylases and show that they down-regulate JA-dependent responses. As they are induced by JA we named them JASMONATE-INDUCED OXYGENASEs (JOXs). Concurrent mutation of the four genes in a quadruple Arabidopsis mutant resulted in increased defense gene expression and increased resistance to the necrotrophic fungus Botrytis cinerea and the caterpillar Mamestra brassicae. In addition, root and shoot growth of the plants was inhibited. Metabolite analysis of leaves showed that loss of function of the four JOX enzymes resulted in over-accumulation of JA and in reduced turnover of JA into 12-OH-JA. Transformation of the quadruple mutant with each JOX gene strongly reduced JA levels, demonstrating that all four JOXs inactivate JA in plants. The in vitro catalysis of 12-OH-JA from JA by recombinant enzyme could be confirmed for three JOXs. The identification of the enzymes responsible for hydroxylation of JA reveals a missing step in JA metabolism, which is important for the inactivation of the hormone and subsequent down-regulation of JA-dependent defenses. SIGNIFICANCE STATEMENTIn plants, the hormone jasmonic acid (JA) is synthesized in response to attack by pathogens and herbivores, leading to activation of defense responses. Rapidly following JA accumulation, the hormone is metabolized, presumably to prevent inhibitive effects of high JA levels on growth and development. The enzymes that directly inactivate JA were so far unknown. Here, we identify four jasmonate-induced oxygenases (JOXs) in Arabidopsis that hydroxylate jasmonic acid to form inactive 12-OH-JA. A mutant that no longer produces the four enzymes hyperaccumulates JA, exhibits reduced growth, and is highly resistant to attackers that are sensitive to JA-dependent defense. The JOX enzymes thus play an important role in determining the amplitude and duration of JA responses to balance the growth-defense tradeoff.peer-reviewed)

Deep Sequencing Reveals Early Reprogramming of Arabidopsis Root Transcriptomes Upon Ralstonia solanacearum Infection

“…Their expression was repressed after R. solanacearum inoculation. Three of four Arabidopsis jasmonate-induced oxygenase genes, whose products inactivate JA through hydroxylation (Caarls et al 2017), were highly expressed in our data. Similarly, the expression of ST2A encoding a hydroxyjasmonate sulfotransferase that inactivates JA functions (Gidda et al 2003) was highly induced at the LR stage.…”

Long non‐coding RNAs associate with jasmonate‐mediated plant defence against herbivores

“…Second, the biosynthetic genes of defence traits and genes involved in the catabolism of JAs are activated 3 hr after elicitation: these were defined as ‘late’ responders. The accumulation of inactive JAs at 3 hr after elicitation is thought to down‐regulate JA perception, which somehow keeps JA signalling in check (Caarls et al, 2017). This kinetic analysis allowed us to predict the function of lncRNAs.…”

Reshaping of the Arabidopsis thaliana proteome landscape and co-regulation of proteins in development and immunity

“…These results lead us to hypothesize that deconjugation and subsequent modification of JA-Ile play an important role in control of the JA pathway in defense against biotrophs as has been shown against the necrotrophic fungus Botrytis cinerea (Caarls et al, 2017). JA/JA-Ile clearance is presumably in some type of equilibrium with JA synthesis because it has been reported that the JA pathway is party to PTI induction and SA accumulation via EDS5 (Mine et al, 2017).…”