Loss of cytosolic NADP-malic enzyme 2 in Arabidopsis thaliana is associated with enhanced susceptibility to Colletotrichum higginsianum.

• While photosynthetic NADP-malic enzyme (NADP-ME) has a prominent role in the C(4) cycle, the biological function of nonphotosynthetic isoforms remains elusive. Here, we analysed the link between Arabidopsis thaliana cytosolic NADP-ME2 and the plant defence response. • Arabidopsis thaliana plants with wild-type and modified NADP-ME2 expression levels were analysed after elicitation with pathogen-associated molecular patterns (PAMPs) and during the interaction with the hemibiotrophic fungal pathogen Colletotrichum higginsianum. • Under normal growth conditions, the lack or gain of NADP-ME2 activity produced large changes in plant metabolite pool sizes without any effect on morphology or development. Total NADP-ME activity and NADP-ME2 transcript level were enhanced after PAMP treatment and pathogen infection. During infection with C. higginsianum, loss-of-function mutants of NADP-ME2 (nadp-me2) showed enhanced susceptibility. Transient apoplastic reactive oxygen species production after elicitation and callose papilla formation after infection were dampened in nadp-me2. Late salicylic acid (SA)-dependent and SA-independent defence responses were not affected. • Taken together, our results indicate that NADP-ME2 is an important player in plant basal defence, where it appears to be involved in the generation of Moreover, NADP-ME2 was found to be dispensable for later defence responses.

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