Study of the role of a tomato wall-associated kinase (SlWAK1) in the defense against Pseudomonas syringae pv. tomato

POMBO, MARINA A.; MARTIN, GREGORY B.; ROSLI, HERNAN G.

Salta

Congreso; LV Annual SAIB Meeting and XIV PABMB Congress; 2019

Plants count on a two-layered immune system to control and restrict pathogens. The first one, pattern-triggered immunity (PTI), is activated when cell surface receptors perceive microbe-associated molecular patterns (MAMPs) such as the epitope flg22 from bacterial flagellin. Certain bacterial pathogens, for example Pseudomonas syringae pv. tomato DC3000 (Pst DC3000), are able to deliver into the cytoplasm nearly 30 effector proteins to suppress PTI and alter metabolic processes in order to proliferate in the apoplast. The second layer of immunity, effector-triggered immunity (ETI), is activated when one of these effectors is perceived by resistance proteins and leads to a hypersensitive response that controls bacterial growth.We have previously identified using a transcriptomic-based approach, SlWAK1 (Solanum lycopersicum Wall-Associated Kinase) as a gene whose expression is induced by flagellin perception and suppressed by two Pst DC3000 effectors, AvrPto and AvrPtoB. To test its participation in plant immunity we silenced Nicotiana benthamiana plants using virus-induced gene silencing (VIGS) with an SlWAK1-based construct. Silencing resulted in plants with a compromised PTI, higher leaf bacterial titers and more severe disease symptoms. The altered PTI phenotype was also observed when using for VIGS 2 alternative constructs based on the N. benthamiana orthologs. Induction with flg22 epitope, in spite of activating transcriptionally SlWAK1, lead to finding no difference (silenced vs control plants) in symptoms when challenged with Pst DC3000. Immunity induction using a mutant lacking flagellin (ΔfliC) and later on challenge with Pst DC3000 resulted in no symptom difference between SlWAK1-silenced and controls plants, suggesting that flagellin induction is required for full functionality of the SlWAK1-mediated pathway. Furthermore, induction with autoclaved P. fluorescens 55 (a strong inducer of PTI) resulted in no symptom difference between silenced and control plants, indicating that a live inducer is required for observing the phenotype of compromised PTI. Taken together our results indicate that flagellin-mediated PTI is required for SlWAK1 transcriptional activation and that some other ligand could be perceived through SlWAK1 leading to a more robust or prolonged PTI.