The role of phospholipid signalling in the defence of plants against pathogens

Plants are sessile organisms and need to respond quickly to environmental stresses. The innate immune system of plants allows sensing the presence of pathogens, resulting in a defence response that prevents infection. Elicitors produced by the pathogen are specifically recognized by host-encoded receptorlike resistance (R) proteins. The R_protein Cf-4 from tomato is responsible for the recognition of the Avr4 protein elicitor produced by the leaf mold fungus Cladosporium fulvum. The receptor-like part of the Cf-4 protein, consisting of leucine rich repeats, is on the outside of the cell (where it can mediate recognition of Avr4), whereas the remainder, a short C-terminal stretch of amino acids, is inside the cell (where it is thought to initiate a defence response). Our group studies the early signalling processes that are initiated by Cf-4 inside the cell after Avr4 recognition. It was found that a very early response of Cf-4-expressing cells (within five minutes after exposure to Avr4) is the activation of two enzymes involved in phospholipid signalling; phospholipase-C (PLC) and diacylglycerol kinase (DGK). As a result of this activation, phosphatidic acid (PA) rapidly accumulates which could act as a second messenger able to initiate responses further downstream. We revealed that PLC and DGK are required for an effective defence response to C. fulvum. Accordingly, we aim to identify and characterise the PLC and DGK gene families of tomato. The identified genes will be individually silenced or over-expressed and the effect of such manipulation on disease resistance will be studied. Once the key members of the PLC and DGK families playing a role in disease resistance have been identified, we will study both the mechanism by which the encoded enzymes are activated and their role in phospholipid signalling upon pathogen recognition