The role of CYP71A12 monooxygenase in pathogen-triggered tryptophan metabolism and Arabidopsis immunity

13 Pág.Effective defense of Arabidopsis against filamentous pathogens requires two mechanisms, both of which involve biosynthesis of tryptophan (Trp)-derived metabolites. Extracellular resistance involves products of PEN2-dependent metabolism of indole glucosinolates (IGs). Restriction of further fungal growth requires PAD3-dependent camalexin and other, as yet uncharacterized, indolics. This study focuses on the function of CYP71A12 monooxygenase in pathogen-triggered Trp metabolism, including the biosynthesis of indole-3-carboxylic acid (ICA). Moreover, to investigate the contribution of CYP71A12 and its products to Arabidopsis immunity, we analyzed infection phenotypes of multiple mutant lines combining pen2 with pad3, cyp71A12, cyp71A13 or cyp82C2. Metabolite profiling of cyp71A12 lines revealed a reduction in ICA accumulation. Additionally, analysis of mutant plants showed that low amounts of ICA can form during an immune response by CYP71B6/AAO1-dependent metabolism of indole acetonitrile, but not via IG hydrolysis. Infection assays with Plectosphaerella cucumerina and Colletotrichum tropicale, two pathogens with different lifestyles, revealed cyp71A12-, cyp71A13- and cyp82C2-associated defects associated with Arabidopsis immunity. Our results indicate that CYP71A12, but not CYP71A13, is the major enzyme responsible for the accumulation of ICA in Arabidopsis in response to pathogen ingression. We also show that both enzymes are key players in the resistance of Arabidopsis against selected filamentous pathogens after they invade.This work was supported by the National Science Centre SONATA BIS grant (UMO-2012/07/E/NZ2/04098) to PB and PRELUDIUM grant (UMO-2013/09/N/NZ2/02080) to KK, and Spanish Ministry of Economy and Competitiveness (MINECO) grant BIO2015-64077-R to AM, and Grants-in-Aid for Scientific Research (18H04780, 18K19212) (KAKENHI) and the Asahi Glass Foundation to YT. EG has been supported by a Heisenberg Fellowship of the Deutsche Forschungsgemeinschaft (GL346/5) and the TUM Junior Fellow Fund.Peer reviewe

Glucosinolate Regulation in a Complex Relationship - MYC and MYB - No One Can Act Without Each Other

The well-studied pathway of glucosinolate (GSL) biosynthesis in Arabidopsis thaliana serves as a model system for secondary metabolites in plants. Most biosynthetic genes are known and were used in systematic co-expression approaches to identify their transcriptional regulators. Two groups of homologous MYB and bHLH transcription factors (TFs) interact with each other and fulfil the main role of direct regulation. The MYB factors are crucial for the specificity of the pathway and control genes in the core-structure pathway of indolic and aliphatic GSL, respectively, as well as the genes in the primary metabolism for the necessary substrates. The MYC-bHLH TFs are crucial for all types of GSL and act together with both types of MYB factors; furthermore they integrate phytohormone signals specifically from the jasmonate signal transduction to adjust the production of this important defence compound class. The regulation of the modification reactions of GSL is under control of a diverse set of other TFs, which have the potential to fine-tune also the core-structure pathway of the glucosinolate biosynthesis. However, most of these regulators still need to be identified and characterized. Although many aspects and components involved in this transcriptional regulation are known, still not all known glucosinolate profiles can be explained by the activity of these modulators and point to the important role of transport and metabolism in determining accumulation pattern of GSL