Identification of new transcription factors involved in tomato defense against Pseudomonas syringae pv. tomato (Pst)

SIRVENT, EMILIA; ROSLI, HERNÁN GUILLERMO; POMBO, MARINA ALEJANDRA

Congreso; LVIII Reunión Anual SAIB; 2022

During their life cycle, plants are exposed to a wide variety of pathogens and to defend themselves they have evolved a two-layered immune system. The first barrier is called PTI (pattern-triggered immunity) and is activated upon the recognition of MAMPs (microbe-associated molecular patterns) by plants' PRRs (pattern-recognition receptors) located on the cell's surface. In early stages of the infection, tomato detects mainly two flagellin MAMPs with receptors flagellin sensing 2 (FLS2) and flagellin sensing 3 (FLS3) which recognise flg22 and flgII-28 respectively, leading to PTI activation. Virulent pathogens like Pst can deliver effector proteins into the cytoplasm to promote susceptibility. However some plants have evolved a second layer of immunity called ETI (effector-triggered immunity) which requires resistance proteins (R) that can recognise these effectors and activate a fast and localized response that culminates in a hypersensitive response (HR) where infected cells die to contain pathogen infection. Tomato Rio Grande Pto-R plants detect two Pst effectors (AvrPto and AvrPtoB) with a two protein complex Pto/Prf which lead to ETI activation.PTI and ETI activation include large transcriptional changes. Current studies mainly focus on a few transcription factors (TF) families such as bHLH, MYB, WRKY, AP2/ERF and NAC. We wonder if there are other TFs outside these families that have not yet been implicated in plant immunity, regulating key processes in plant defense against bacteria. In previous studies we identified around 300 genes that encode for TFs whose expression is increased due to the treatment with MAMPs and Pst mutants. With this information we propose to identify and characterize new TFs implicated in the regulation of tomato defense against Pst, with special emphasis in those belonging to families not previously linked to the defense response. We selected five TFs (ERF30, Ethylene responsive factor 30; HSF, Heat shock factor; LBS, LOB domain protein; DBP, DNA binding Phosphatase; OFP, Ovate family protein) and silenced their orthologous genes in Nicotiana benthamiana (Nb) using VIGS (virus-induced gene silencing) technique. To assess their implication in ETI, silenced plants were infiltrated with a combination of A. tumefaciens GV2260, one which possesses pBTEX::pto vector, and another one with pBTEX::avrPto, that strongly induce macroscopic HR. Plants silenced for ERF30 and HSF showed a delay in HR development compared to control plants. Next, Nb plants expressing 35S:Pto transgene were silenced with our candidate constructs and infiltrated with P. s. pv. tabaci strains carrying AvrPto or an empty vector as control. Plants silenced with ERF30 and HSF showed increased disease symptoms compared to control plants. Together, these experiments suggest that TFs ERF30 and HSF may play a role on plant defense response signaling pathways against Pst infection.