Multiple Xanthomonas euvesicatoria Type III Effectors Inhibit flg22-Triggered Immunity

Area of Science:

• Plant Pathology
• Microbial Genetics
• Molecular Plant-Microbe Interactions

Background:

• Xanthomonas euvesicatoria causes bacterial spot disease in pepper and tomato.
• The type III secretion (T3S) system delivers effector proteins into host cells, aiding pathogen survival.
• Some T3S effectors suppress plant pattern-triggered immunity (PTI), a crucial defense mechanism.

Purpose of the Study:

• To identify X. euvesicatoria 85-10 T3S effectors that interfere with PTI signaling.
• To investigate the molecular mechanisms by which these effectors suppress plant immunity.

Main Methods:

• Arabidopsis thaliana and tomato protoplast-based assays were used to screen for effectors inhibiting PTI signaling.
• Promoter activation assays and mitogen-activated protein (MAP) kinase phosphorylation assays were performed.
• In planta assays measured callose deposition and disease symptoms.

Main Results:

• 17 out of 33 tested X. euvesicatoria T3S effectors inhibited PTI signaling.
• Nine effectors also interfered with abscisic acid signaling pathways.
• Key effectors (XopAJ, XopE2, XopF2) suppressed PTI in both Arabidopsis and tomato, acting downstream or parallel to MAP kinase cascades.
• Several effectors enhanced disease symptoms and suppressed callose deposition in planta.

Conclusions:

• X. euvesicatoria employs multiple T3S effectors to suppress flg22-induced PTI signaling.
• These effectors likely act through diverse molecular mechanisms.
• Understanding these effectors provides insights into bacterial pathogenesis and plant immune evasion strategies.