Anti-idiotypic antibodies can mimic the ability of Phytophthora infestans to induce the accumulation of transcripts associated with defence responsesin potato

The initial infection process involving adhesion/recognition events between plants and fungal pathogens is essential for the establishment of pathogen esis. The basis of the specificity between Phytophthora infestans and potat o is not yet known. It could lie in the recognition between extracellular m atrix and plasma membrane components of the penetrating structures of the f ungus and host cells during the earliest stages of infection processes. We have used polyclonal antibodies (AZ and AC) obtained after immunizing rabbi ts with either 10(7) zoospores (Z) or germinating cysts (C) of P. infestans to detect putative fungal components located on the surface of invasive st ructures. AZ recognized several bands, while AC recognized three polypeptid es of approximately 87, 73 and 45 kDa in western blots. Zoospore suspension s preincubated either with AZ or AC were unable to infect potato leaves. Si nce it was already known that some anti-idiotypic (anti-IT) antibodies may resemble the antigen, thus mimicking its structure, anti-IT antibodies (a-A Z and a-AC) were generated in mice and used as inducers on potato tuber dis cs. In northern blots a-AZ treatments increased 1.5-fold the glyceraldehyde -3-P dehydrogenase (GAPDH) and 1.8-fold the phenylalanine ammonia-lyase (PA L) transcript levels, while an increase of 1.8 and 1.7-fold for GAPDH and P AL, respectively, was observed when the inducer was a-AC. Both PAL and GAPD H transcript levels have previously been shown to be modulated by Fungal an d elicitor: treatments. These results show that the anti-idiotypic antibodi es are able to mimic the pathogen components, leading to the accumulation o f transcripts related to defence responses in potato-P. infestans interacti on. (C) 1998 Academic Press.