Identification of Pseudomonas syringae pv. tomato genes induced during infection of Arabidopsis thaliana

• Published in: Molecular microbiology Vol. 44; no. 1; pp. 73 - 88
• Main Authors: Boch, Jens, Joardar, Vinita, Gao, Lisa, Robertson, Tara L., Lim, Melisa, Kunkel, Barbara N.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science Ltd 01-04-2002; Blackwell Publishing Ltd
• Subjects: Arabidopsis - microbiology; Gene Deletion; Gene Expression Regulation, Bacterial; Genes, Reporter; Glucuronidase - genetics; Mutagenesis, Insertional; Plant Diseases - microbiology; Promoter Regions, Genetic; Pseudomonas - genetics; Pseudomonas - growth & development; Pseudomonas - pathogenicity
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1046/j.1365-2958.2002.02877.x

Summary
Phytopathogenic bacteria possess a large number of genes that allow them to grow and cause disease on plants. Many of these genes should be induced when the bacteria come in contact with plant tissue. We used a modified in vivo expression technology
(IVET) approach to identify genes from the plant pathogen Pseudomonas syringae
pv. tomato that are induced upon infection of Arabidopsis thaliana
and isolated over 500 in planta‐expressed (ipx) promoter fusions. Sequence
analysis of 79 fusions revealed several known and potential virulence genes, including
hrp/hrc, avr and coronatine biosynthetic genes. In addition, we identified
metabolic genes presumably important for adaptation to growth in plant tissue, as
well as several genes with unknown function that may encode novel virulence factors.
Many ipx fusions, including several corresponding to novel genes, are dependent
on HrpL, an alternative RNA polymerase sigma factor that regulates the expression
of virulence genes. Expression analysis indicated that several ipx fusions
are strongly induced upon inoculation into plant tissue. Disruption of one ipx
gene, conserved effector locus (CEL) orf1, encoding a putative lytic murein
transglycosylase, resulted in decreased virulence of P. syringae. Our results
demonstrate that this screen can be used successfully to isolate genes that are induced
in planta, including many novel genes potentially involved in pathogenesis.