Arginase Induction Represses Gall Development During Clubroot Infection in Arabidopsis

Arginase induction can play a defensive role through the reduction of arginine availability for phytophageous insects. Arginase activity is also induced during gall growth caused by Plasmodiophora brassicae infection in roots of Arabidopsis thaliana; however, its possible role in this context has been unclear. We report here that the mutation of the arginase-encoding gene ARGAH2 abrogates clubroot-induced arginase activity and results in enhanced gall size in infected roots, suggesting that arginase plays a defensive role. Induction of arginase activity in infected roots was impaired in the jar1 mutant, highlighting a link between the arginase response to clubroot and jasmonate signaling. Clubroot-induced accumulation of the principal amino acids in galls was not affected by the argah2 mutation. Because ARGAH2 was previously reported to control auxin response, we investigated the role of ARGAH2 in callus induction. ARGAH2 was found to be highly induced in auxin/cytokinin-triggered aseptic plant calli, and callus development was enhanced in argah2 in the absence of the pathogen. We hypothesized that arginase contributes to a negative control over clubroot symptoms, by reducing hormone-triggered cellular proliferation.