We have used site-directed mutagenesis and agroinfiltration to investigate molecular function in the tomato Cf-9 protein conferring leaf mould resistance.
The tomato Cf-9 gene encodes a membrane-anchored receptor-like protein that confers resistance to tomato leaf mould (pictured). Cf-9 has a small cytosolic domain that contains short motifs that may be involved in quality control, sorting and signalling. Previously, we have shown that a C-terminal KKxx motif functions as an ER retention signal that may be involved in Cf-9 quality control (Benghezal et al. 2000).
Recently, we have been investigating the role of a potential YxxPhi motif, which may function as an endocytosis signal. We have used site-directed mutagenesis to conduct an alanine scan of the region containing the potential YxxPhi motif and used agroinfiltration (infiltration with Agrobacterium) to assay the mutant Cf-9 proteins in the leaves of Avr9 tobacco plants. Our data suggest that the cytosolic domain of Cf-9 plays an important role in Cf-9 signalling, but, contrary to other reports, do not support an important role for the YxxPhi motif or endocytosis in signalling (Chakrabarti et al. in preparation).