Polygalacturonase inhibitor protein from fruits of anthracnose resistant and susceptible varieties of Chilli (Capsicum annuum L)

Chilli fruit is highly susceptible to anthracnose infection A the stage of harvest maturity, due to which the fruit yield in the leading commercial variety Byadgi is severely affected. Field studies on screening of several varieties for resistance to anthracnose have shown that a variety of chilli AR-4/99K is resistant to anthracnose infection. In many crops, resistance to fungal attack has been correlated with PGIP activity in developing fruits based on which transgenic varieties have been developed with resistance to fungi. The present study was carried out to determine whether anthracnose resistance in AR-4/99K was due to the increased levels of PGIP alone and/or due to differences, if any, in the properties of PGIP. Hence, a comparative study of the properties of polygalacturonase inhibitor protein (PGIP) isolated from fruits of anthracnose resistant chilli var AR-4/99K and a susceptible variety Byadgi was conducted with the objective of utilizing the information in genetic transformation studies. Both the PGIPs from anthracnose resistant and susceptible varieties of chilli exhibited similarities in the elution pattern on Sephadex gel, DEAF cellulose, PAGE and SDS-PAGE. The two PGIPs were active over a wide range of pH and temperature. Both PGIPs showed differential inhibitory activity against polygalacturonase (PG) secreted by Colletotrichum gleosporoides, C. capsici, C. lindemuthianum, Fusarium moniliforme and Sclerotium rolfsii. The inhibitory activity of PGIP from both resistant and susceptible varieties was the highest (82% and 76%, respectively) against the PG from Colletotrichum capsici, a pathogen causing anthracnose rot of chilli, while the activity was lower (1.27 to 12.3%) on the other fungal PGs. Although PGIP activity decreased with fruit maturation in both the varieties, the resistant variety maintained a higher activity at 45 days after flowering (DAF) as compared to the susceptible variety which helped it to overcome the infection by anthracnose as against the susceptible variety (Byadgi) in which PGIP activity was drastically reduced at maturity. The molecular mass of PGIP as determined by SDS-PAGE was found to be 37 kDa. N-terminal sequence analysis of the PGIP showed the first six amino acid residues from N-terminal end were Asp-Thr-His-Lys-Ser-Glu (DTHKSE), respectively. The similarities in properties of the two PGIPs support the earlier findings that resistance of AR-4/99K to anthracnose fungus is a result of its higher PGIP activity at maturity.