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Differential Expression of Genes Encoding Arabidopsis Phospholipases After Challenge with Virulent or Avirulent Pseudomonas Isolates

¹Department of Agricultural Sciences, Imperial College at Wye, Wye, Kent TN25 5AH, U.K.; ²INRA de Versailles, Route de Saint-Cyr, 78026 Versailles Cedex, France; ³John Innes Centre, Norwich Research Park. Colney Lane, Norwich, NR4 7UH, U.K.; ⁴Department of Biochemistry, University of Bath, Bath BA2 7AY, U.K.

Phospholipase D (PLD; EC 3.1.4.4) has been linked to a number of cellular processes, including Tran membrane signaling and membrane degradation. Four PLD genes (α, β, γ1, and γ2) have been cloned from Arabidopsis thalami. They encode isoforms with distinct regulatory and catalytic properties but little is known about their physiological roles. Using cDNA amplified fragment length polymorphism display and RNA blot analysis, we identified Arabidopsis PLDγ1 and a gene encoding a lysophospholipase (EC 3.1.1.5), lysoPL1, to be differentially expressed during host response to virulent and avirulent pathogen challenge. Examination of the expression pattern of phospholipase genes induced in response to pathogen challenge was undertaken using the lysoPL1 and gene-specific probes corresponding to the PLD isoforms α, β, and γ1. Each mRNA class exhibited different temporal patterns of expression after infiltration of leaves with Pseudomonas syringae pv. tomato with or without avrRpm1. PLDα was rapidly induced and remained constitutively elevated regardless of treatment. PLDβ was transiently induced upon pathogen challenge. However, mRNA for the lysoPL1 and PLDγ1 genes showed enhanced and sustained elevation during an incompatible interaction, in both ndr1 and overexpressing NahG genetic backgrounds. Further evidence for differential engagement of these PLD mRNA during defense responses, other than gene-for-gene interactions, was demonstrated by their response to salicylic acid treatment or wounding. Our results indicate that genes encoding lysoPL1, PLDγ1, and PLDβ are induced during early responses to pathogen challenge and, additionally, PLDγ1 and lysoPL1 are specifically upregulated during gene-for-gene interactions, leading to the hypersensitive response. We discuss the possible role of these genes in plant-pathogen interactions.

Additional keyword: RPM1 .