title: TALE-induced bHLH transcription factors that activate a pectate lyase contribute to water soaking in bacterial spot of tomato.
abstract: AvrHah1 [avirulence (avr) gene homologous to avrBs3 and hax2, no. 1] is a transcription activator-like (TAL) effector (TALE) in Xanthomonas gardneri that induces water-soaked disease lesions on fruits and leaves during bacterial spot of tomato. We observe that water from outside the leaf is drawn into the apoplast in X. gardneri-infected, but not X. gardneriΔavrHah1 (XgΔavrHah1)-infected, plants, conferring a dark, water-soaked appearance. The pull of water can facilitate entry of additional bacterial cells into the apoplast. Comparing the transcriptomes of tomato infected with X. gardneri vs. XgΔavrHah1 revealed the differential up-regulation of two basic helix-loop-helix (bHLH) transcription factors with predicted effector binding elements (EBEs) for AvrHah1. We mined our RNA-sequencing data for differentially up-regulated genes that could be direct targets of the bHLH transcription factors and therefore indirect targets of AvrHah1. We show that two pectin modification genes, a pectate lyase and pectinesterase, are targets of both bHLH transcription factors. Designer TALEs (dTALEs) for the bHLH transcription factors and the pectate lyase, but not for the pectinesterase, complement water soaking when delivered by XgΔavrHah1 By perturbing transcriptional networks and/or modifying the plant cell wall, AvrHah1 may promote water uptake to enhance tissue damage and eventual bacterial egression from the apoplast to the leaf surface. Understanding how disease symptoms develop may be a useful tool for improving the tolerance of crops from damaging disease lesions.
authors.affiliation: Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720-3120.
authors.forename: Allison R
authors.initials: AR
authors.lastname: Schwartz
authors.affiliation: Department of General Genetics, Center of Plant Molecular Biology, University of Tübingen, D-72076 Tubingen, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Morbitzer
authors.affiliation: Department of General Genetics, Center of Plant Molecular Biology, University of Tübingen, D-72076 Tubingen, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Lahaye
authors.affiliation: Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720-3120; stask@berkeley.edu.
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Staskawicz
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D051792:Basic Helix-Loop-Helix Proteins / Q000502:physiology*; D002212:Capsicum / Q000378:metabolism / Q000382:microbiology*; D004789:Enzyme Activation; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics*; D018506:Gene Expression Regulation, Plant / Q000235:genetics*; D018551:Solanum lycopersicum / Q000378:metabolism / Q000382:microbiology*; D010641:Phenotype; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology*; D018515:Plant Leaves / Q000378:metabolism / Q000382:microbiology; D011133:Polysaccharide-Lyases / Q000235:genetics*; D014026:Nicotiana / Q000378:metabolism / Q000382:microbiology*; D014157:Transcription Factors / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D015854:Up-Regulation; D014774:Virulence; D014867:Water / Q000378:metabolism; D014974:Xanthomonas / Q000235:genetics / Q000472:pathogenicity* / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; D051792:Basic Helix-Loop-Helix Proteins; D011133:Polysaccharide-Lyases; D014157:Transcription Factors; D014867:Water; C023911:pectate lyase
keywords: TAL effector; Xanthomonas bacterial spot; water soaking