Molecular Analysis of the Polygalacturonase-Inhibiting Protein (PGIP) Gene Family in Phaseolus Vulgaris L.

In Phaseolus vulgaris (bean), PGIP is encoded by a gene family. We have isolated cDNA clones corresponding to two different pgip genes (pgip-1 and pgip-2). These genes have been separately expressed in Nicotiana benthamiana using the potato virus X (PVX) as a vector. PGIP-1 and PGIP-2 in crude protein extracts of PVX-infected TV. benthamiana, and a PGIP-1 purified from transgenic tomato plants carrying the pgip-1 coding sequence under the control of the CaMV 35S promoter, have been assayed for specificity of interaction with several fungal PGs. PGIP-1 from both plant sources exhibited a similar specificity, which was different from that of PGIP-2 and of the bulk PGIP purified from bean. Notably, PGIP-1 was unable to interact with homogeneous PG from Fusarium moniliforme, as determined by surface plasmon resonance analysis, while PGIP-2 and the bulk bean PGIP interacted with this enzyme.