Identification of target amino acids that affect interactions of fungal polygalacturonases and their plant inhibitors

Plant polygalacturonase inhibitor proteins (PGIPs) bind fungal polygalactur onases (PGs), but inhibition specificities and kinetics vary within and amo ng species. Purified bean PGIP inhibited all fungal PGs we tested, includin g Fusarium moniliforme PG. Pear PGIP, however, was only effective against B otrytis cinerea PG. Moreover, tomato PGIP inhibited B. cinerea PG more than Aspergillus niger PG. Models of codon evolution for 22 dicot PGIPs and 19 fungal PGs indicated that advantageous substitutions dominate the molecular evolution of these genes and identified 9 amino acid residues, each, that are likely to evolve adaptively in response to natural selection, Many of t hese residues are within the beta-strand/beta-turn region of the PGIP LRR, including two sites known to alter inhibition specificities of bean PGIPs, but others lie outside this region. Our results complement existing molecul ar and biochemical studies of resistance specificity, and suggest new targe t amino acids for manipulating PG-inhibition. (C) 2000 Academic Press.