title: Cooperative functioning between phenylalanine ammonia lyase and isochorismate synthase activities contributes to salicylic acid biosynthesis in soybean.
abstract: Salicylic acid (SA), an essential regulator of plant defense, is derived from chorismate via either the phenylalanine ammonia lyase (PAL) or the isochorismate synthase (ICS) catalyzed steps. The ICS pathway is thought to be the primary contributor of defense-related SA, at least in Arabidopsis. We investigated the relative contributions of PAL and ICS to defense-related SA accumulation in soybean (Glycine max). Soybean plants silenced for five PAL isoforms or two ICS isoforms were analyzed for SA concentrations and SA-derived defense responses to the hemibiotrophic pathogens Pseudomonas syringae and Phytophthora sojae. We show that, unlike in Arabidopsis, PAL and ICS pathways are equally important for pathogen-induced SA biosynthesis in soybean. Knock-down of either pathway shuts down SA biosynthesis and abrogates pathogen resistance. Moreover, unlike in Arabidopsis, pathogen infection is associated with the suppression of ICS gene expression. Pathogen-induced biosynthesis of SA via the PAL pathway correlates inversely with phenylalanine concentrations. Although infections with either virulent or avirulent strains of the pathogens increase SA concentrations, resistance protein-mediated response to avirulent P. sojae strains may function in an SA-independent manner. These results show that PAL- and ICS-catalyzed reactions function cooperatively in soybean defense and highlight the importance of PAL in pathogen-induced SA biosynthesis.
authors.affiliation: Department of Plant Pathology, University of Kentucky, Lexington, KY, 40546, USA.
authors.forename: M B
authors.initials: MB
authors.lastname: Shine
authors.affiliation: Department of Plant Pathology, University of Kentucky, Lexington, KY, 40546, USA.
authors.forename: Jung-Wook
authors.initials: JW
authors.lastname: Yang
authors.affiliation: Department of Plant Pathology, University of Kentucky, Lexington, KY, 40546, USA.
authors.forename: Mohamed
authors.initials: M
authors.lastname: El-Habbak
authors.affiliation: Department of Plant Pathology, University of Kentucky, Lexington, KY, 40546, USA.
authors.forename: Padmaja
authors.initials: P
authors.lastname: Nagyabhyru
authors.affiliation: Department of Plant Pathology, University of Kentucky, Lexington, KY, 40546, USA.
authors.forename: Da-Qi
authors.initials: DQ
authors.lastname: Fu
authors.affiliation: Department of Plant Pathology, USDA-Agricultural Research Service, Washington State University, Prosser, WA, 99350, USA.
authors.forename: Duroy
authors.initials: D
authors.lastname: Navarre
authors.affiliation: Department of Plant Pathology, University of Kentucky, Lexington, KY, 40546, USA.
authors.forename: Said
authors.initials: S
authors.lastname: Ghabrial
authors.affiliation: Department of Plant Pathology, University of Kentucky, Lexington, KY, 40546, USA.
authors.forename: Pradeep
authors.initials: P
authors.lastname: Kachroo
authors.affiliation: Department of Plant Pathology, University of Kentucky, Lexington, KY, 40546, USA. apkach2@uky.edu.
authors.forename: Aardra
authors.initials: A
authors.lastname: Kachroo
mesh_terms: D053898:Biosynthetic Pathways; D060467:Disease Resistance / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D020868:Gene Silencing; D017343:Genes, Plant; D019751:Intramolecular Transferases / Q000235:genetics / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism; D010650:Phenylalanine Ammonia-Lyase / Q000235:genetics / Q000378:metabolism*; D010838:Phytophthora / Q000502:physiology; D010935:Plant Diseases; D018515:Plant Leaves / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D044224:Pseudomonas syringae / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020156:Salicylic Acid / Q000378:metabolism*; D013025:Glycine max / Q000201:enzymology* / Q000235:genetics / Q000382:microbiology
chemical_list: D007527:Isoenzymes; D010940:Plant Proteins; D012333:RNA, Messenger; D010650:Phenylalanine Ammonia-Lyase; D019751:Intramolecular Transferases; C058486:isochorismate synthase; D020156:Salicylic Acid
keywords: isochorismate synthase (ICS); pathogen defense; phenylalanine ammonia lyase (PAL); salicylic acid (SA); soybean (Glycine max)