Systemic acquired tolerance to virulent bacterial pathogens in tomato

Area of Science:

• Plant pathology
• Molecular plant-microbe interactions
• Plant signaling

Background:

• Plant disease symptoms can result from host responses, not just pathogen growth.
• Phytohormones like ethylene and salicylic acid (SA) mediate these host responses.
• The role of host responses in systemic defense signaling requires further investigation.

Purpose of the Study:

• To investigate the systemic responses of tomato (Lycopersicon esculentum) to Xanthomonas campestris pv vesicatoria (Xcv).
• To determine the involvement of ethylene and SA in mediating systemic acquired tolerance (SAT).
• To characterize the effects of SAT on pathogen growth and host tissue damage.

Main Methods:

• Utilized SA- and ethylene-deficient transgenic tomato lines.
• Inoculated plants with virulent and avirulent strains of Xcv.
• Assessed the expression of pathogenesis-related genes.
• Evaluated bacterial growth and tissue damage upon subsequent pathogen challenge.

Main Results:

• A systemic response, dependent on ethylene and SA, was induced by Xcv infection.
• This systemic response reduced cell death (tissue damage) but did not inhibit bacterial growth upon subsequent challenge.
• Systemic acquired tolerance (SAT) was observed, characterized by reduced tissue damage without affecting pathogen proliferation.
• SAT could also be induced by Pseudomonas syringae pv tomato.

Conclusions:

• Plant systemic acquired tolerance (SAT) is a defense mechanism that mitigates disease symptoms without directly inhibiting pathogen growth.
• Ethylene and salicylic acid play crucial roles in the induction and manifestation of SAT.
• SAT represents a distinct plant defense strategy, differing from systemic acquired resistance (SAR) in its lack of pathogen growth inhibition.