No evidence for binding between resistance gene product Cf-9 of tomato andavirulence gene product AVR9 of Cladosporium fulvum

The gene-for-gene model postulates that for every gene determining resistan ce in the host plant, there is a corresponding gene conditioning avirulence in the pathogen. On the basis of this relationship, products of resistance (R) genes and matching avirulence (Avr) genes are predicted to interact. H ere, we report on binding studies between the R gene product Cf-9 of tomato and the Avr gene product AVR9 of the pathogenic fungus Cladosporium fulvum . Because a high-affinity binding site (HABS) for AVR9 is present in tomato lines, with or without the Cf-9 resistance gene, as well as in other solan aceous plants, the Cf-9 protein was produced in COS and insect cells in ord er to perform binding studies in the absence of the HABS, Binding studies w ith radiolabeled AVR9 were performed with Cf-9-producing COS and insect cel ls and with membrane preparations of such cells. Furthermore, the Cf-9 gene was introduced in tobacco, which is known to be able to produce a function al Cf-9 protein. Binding of AVR9 to Cf-9 protein produced in tobacco was st udied employing surface plasmon resonance and surface-enhanced laser desorp tion and ionization. Specific binding between Cf-9 and AVR9 was not detecte d with any of the procedures. The implications of this observation are disc ussed.