The root-knot nematode effector MiMSP32 targets host 12-oxophytodienoate reductase 2 to regulate plant susceptibility

To establish persistent infections in host plants, herbivorous invaders, such as root-knot nematodes, must rely on effectors for suppressing damage-induced jasmonate-dependent host defenses. However, at present, the effector mechanisms targeting the biosynthesis of biologically active jasmonates to avoid adverse host responses are unknown. Using yeast two-hybrid, in planta co-immunoprecipitation, and mutant analyses, we identified 12-oxophytodienoate reductase 2 (OPR2) as an important host target of the stylet-secreted effector MiMSP32 of the root-knot nematode Meloidogyne incognita. MiMSP32 has no informative sequence similarities with other functionally annotated genes but was selected for the discovery of novel effector mechanisms based on evidence of positive, diversifying selection. OPR2 catalyzes the conversion of a derivative of 12-oxophytodienoate to jasmonic acid (JA) and operates parallel to 12-oxophytodienoate reductase 3 (OPR3), which controls the main pathway in the biosynthesis of jasmonates. We show that MiMSP32 targets OPR2 to promote parasitism of M. incognita in host plants independent of OPR3-mediated JA biosynthesis. Artificially manipulating the conversion of the 12-oxophytodienoate by OPRs increases susceptibility to multiple unrelated plant invaders. Our study is the first to shed light on a novel effector mechanism targeting this process to regulate the susceptibility of host plants.

A maize death acid, 10-oxo-11-phytoenoic acid, is the predominant cyclopentenone signal present during multiple stress and developmental conditions

Recently we investigated the function of the 9-lipoxygenase (LOX) derived cyclopentenones 10-oxo-11-phytoenoic acid (10-OPEA) and 10-oxo-11,15-phytodienoic acid (10-OPDA) and identified their C-14 and C-12 derivatives. 10-OPEA accumulation is elicited by fungal and insect attack and acts as a strong inhibitor of microbial and herbivore growth. Although structurally similar, comparative analyses between 10-OPEA and its 13-LOX analog 12-oxo-phytodienoic acid (12-OPDA) demonstrate specificity in transcript accumulation linked to detoxification, secondary metabolism, jasmonate regulation, and protease inhibition. As a potent cell death signal, 10-OPEA activates cysteine protease activity leading to ion leakage and apoptotic-like DNA fragmentation. In this study we further elucidate the distribution, abundance, and functional roles of 10-OPEA, 10-OPDA, and 12-OPDA, in diverse organs under pathogen- and insect-related stress.

Crystal structure of 12-oxophytodienoate reductase 3 from tomato: self-inhibition by dimerization

12-Oxophytodienoate reductase (OPR) 3, a homologue of old yellow enzyme (OYE), catalyzes the reduction of 9S,13S-12-oxophytodienoate to the corresponding cyclopentanone, which is subsequently converted to the plant hormone jasmonic acid (JA). JA and JA derivatives, as well as 12-oxophytodienoate and related cyclopentenones, are known to regulate gene expression in plant development and defense. Together with other oxygenated fatty acid derivatives, they form the oxylipin signature in plants, which resembles the pool of prostaglandins in animals. Here, we report the crystal structure of OPR3 from tomato and of two OPR3 mutants. Although the catalytic residues of OPR3 and related OYEs are highly conserved, several characteristic differences can be discerned in the substrate-binding regions, explaining the remarkable substrate stereoselectivity of OPR isozymes. Interestingly, OPR3 crystallized as an extraordinary self-inhibited dimer. Mutagenesis studies and biochemical analysis confirmed a weak dimerization of OPR3 in vitro, which correlated with a loss of enzymatic activity. Based on structural data of OPR3, a putative mechanism for a strong and reversible dimerization of OPR3 in vivo that involves phosphorylation of OPR3 is suggested. This mechanism could contribute to the shaping of the oxylipin signature, which is critical for fine-tuning gene expression in plants.