Differential expression analysis of a select list of genes in susceptible and resistant heirloom tomatoes with respect to Pseudomonas syringae pv. tomato

Abstract

Bacterial speck disease of tomato, caused by Pseudomonas syringae pv. tomato (Pst) is one of the most devastating diseases of tomato in the world. To investigate plant responses activated during plant-pathogen interaction, we studied the expression analysis of selected defense-response genes and the microbe or pathogen associated molecular patterns (MAMP or PAMP) triggered immunity (PTI) marker genes in heirloom tomatoes challenged with virulent Pst DC3000. Transcript levels of the defense response genes, including SlPR1a (pathogenesis related proteins), SlPR-Q′b (β-1,3-glucanase), SlGST (Glutathione S-transferase) and peroxidase were up-regulated in the resistant cultivars Orange Strawberry and Amishpaste. The PTI marker genes SlPTI5 (encode a pathogen-inducible ethylene response element-binding protein-like transcription factor) and SlFLS2 (a leucine rich-repeat receptor like kinase) were strongly up-regulated in the incompatible reaction to resistant cultivar Orange Strawberry. On the other hand, transcripts from all tested genes were down-regulated in the compatible interaction in susceptible cultivars Yellow Pear and Brandywine. The induction of defense response and PTI marker genes occurred in the early infection process at 3 days post-inoculation (dpi) and consistent with lower levels of disease severity in resistant cultivars was observed than in susceptible cultivars. Our results contribute to the body of information on bacterial speck disease resistance in an economically important crop tomato.