title: Identification of likely orthologs of tobacco salicylic acid-binding protein 2 and their role in systemic acquired resistance in Arabidopsis thaliana.
abstract: Salicylic acid-binding protein 2 (SABP2) is essential for the establishment of systemic acquired resistance (SAR) in tobacco; SABP2's methyl salicylate (MeSA) esterase activity is required in healthy systemic tissues of infected plants to release the active defense phytohormone SA from MeSA, which serves as a long-distance signal for SAR. In the current study, we characterize a new gene family from Arabidopsis thaliana encoding 18 potentially active alpha/beta fold hydrolases that share 32-57% identity with SABP2. Of 14 recombinant AtMES (MES for methyl esterase) proteins tested, five showed preference for MeSA as a substrate and displayed SA inhibition of MeSA esterase activity in vitro (AtMES1, -2, -4, -7, and -9). The two genes encoding MeSA esterases with the greatest activity, AtMES1 and -9, as well as AtMES7 were transcriptionally upregulated during infection of Arabidopsis with avirulent Pseudomonas syringae. In addition, conditional expression of AtMES1, -7, or -9 complemented SAR deficiency in SABP2-silenced tobacco, suggesting that these three members of the AtMES family are SABP2 functional homologs (orthologs). Underexpression by knockout mutation and/or RNAi-mediated silencing of multiple AtMES genes, including AtMES1, -2, -7, and -9, compromised SAR in Arabidopsis and correlated with enhanced accumulation of MeSA in the systemic tissue of SAR-induced plants. Together, the data show that several members of the AtMES gene family are functionally homologous to SABP2 and redundant for MeSA hydrolysis and probably SAR. These data suggest that MeSA is a conserved SAR signal in Arabidopsis and tobacco.
authors.affiliation: Boyce Thompson Institute for Plant Research, Tower Road, Ithaca, NY 14853, USA.
authors.forename: Anna Corina
authors.initials: AC
authors.lastname: Vlot
authors.forename: Po-Pu
authors.initials: PP
authors.lastname: Liu
authors.forename: Robin K
authors.initials: RK
authors.lastname: Cameron
authors.forename: Sang-Wook
authors.initials: SW
authors.lastname: Park
authors.forename: Yue
authors.initials: Y
authors.lastname: Yang
authors.forename: Dhirendra
authors.initials: D
authors.lastname: Kumar
authors.forename: Fasong
authors.initials: F
authors.lastname: Zhou
authors.forename: Thihan
authors.initials: T
authors.lastname: Padukkavidana
authors.forename: Claes
authors.initials: C
authors.lastname: Gustafsson
authors.forename: Eran
authors.initials: E
authors.lastname: Pichersky
authors.forename: Daniel F
authors.initials: DF
authors.lastname: Klessig
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics* / Q000276:immunology / Q000382:microbiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D004950:Esterases / Q000235:genetics*; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D007113:Immunity, Innate; D005810:Multigene Family; D010940:Plant Proteins / Q000235:genetics*; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics / Q000276:immunology / Q000382:microbiology; D044224:Pseudomonas syringae / Q000502:physiology; D034622:RNA Interference; D018749:RNA, Plant / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012459:Salicylates / Q000378:metabolism; D013379:Substrate Specificity; D014026:Nicotiana / Q000235:genetics; D014170:Transformation, Genetic; D019076:Transgenes
chemical_list: D029681:Arabidopsis Proteins; D010940:Plant Proteins; D018749:RNA, Plant; D012459:Salicylates; C499506:SABP2 protein, Nicotiana tabacum; D004950:Esterases; C033069:methyl salicylate