Structure-guided analysis of Arabidopsis JASMONATE-INDUCED OXYGENASE(JOX)2 reveals key residues for recognition of jasmonic acid substrate by plant JOXs

The jasmonic acid(JA)signaling pathway is used by plants to control wound responses.The persistent accumulation of JA inhibits plant growth,and the hydroxylation of JA to 12-hydroxy-JA by JASMONATE-INDUCED OXYGENASEs(JOXs,also named jasmonic acid oxidases)is therefore vital for plant growth,while structural details of JA recognition by JOXs are unknown.Here,we present the 2.65Åresolution X-ray crystal structure of Arabidopsis JOX2 in complex with its substrate JA and its co-substrates 2-oxoglutarate and Fe(Ⅱ).JOX2 contains a distorted double-stranded p helix(DSBH)core flanked by a helices and loops.JA is bound in the narrow substrate pocket by hydrogen bonds with the arginine triad R225,R350,and R354 and by hydrophobic interactions mainly with the phenylalanine triad F157,F317,and F346.The most critical residues for JA binding are F157 and R225,both from the DSBH core,which interact with the cyclopentane ring of JA.The spatial distribution of critical residues for JA binding and the shape of the substrate-binding pocket together define the substrate selectivity of the JOXs.Sequence alignment shows that these critical residues are conserved among JOXs from higher plants.Collectively,our study provides insights into the mechanism by which higher plants hydroxylate the hormone JA.

Comparative Secretome Analysis of Magnaporthe oryzae Identified Proteins Involved in Virulence and Cell Wall Integrity

Plant fungal pathogens secrete numerous proteins into the apoplast at the plant–fungus contact sites to facilitate colonization.However,only a few secretory proteins were functionally characterized in Magnaporthe oryzae,the fungal pathogen causing rice blast disease worldwide.Asparagine-linked glycosylation 3(Alg3)is an a-1,3-mannosyltransferase functioning in the Nglycan synthesis of N-glycosylated secretory proteins.Fungal pathogenicity and cell wall integrity are impaired inΔalg3 mutants,but the secreted proteins affected inΔalg3 mutants are largely unknown.In this study,we compared the secretomes of the wild-type strain and theΔalg3 mutant and identified 51 proteins that require Alg3 for proper secretion.These proteins were predicted to be involved in metabolic processes,interspecies interactions,cell wall organization,and response to chemicals.Nine proteins were selected for further validation.We found that these proteins were localized at the apoplastic region surrounding the fungal infection hyphae.Moreover,the Nglycosylation of these proteins was significantly changed in theΔalg3 mutant,leading to the decreased protein secretion and abnormal protein localization.Furthermore,we tested the biological functions of two genes,INV1(encoding invertase 1,a secreted invertase)and AMCase(encoding acid mammalian chinitase,a secreted chitinase).The fungal virulence was significantly reduced,and the cell wall integrity was altered in theΔinv1 andΔamcase mutant strains.Moreover,the N-glycosylation was essential for the function and secretion of AMCase.Taken together,our study provides new insight into the role of N-glycosylated secretory proteins in fungal virulence and cell wall integrity.