Research Projects

Papaya ringspot virus (PRSV) belongs to the genus potyvirus, is the cause of destructive disease and is a major global constraint for cucurbits and papaya, production and cultivation worldwide. The disease affects papaya plants at all growth stages and naturally spreads swiftly, leading to the infection of the whole orchard within 3–7 months resulting in catastrophic yield losses of up to 100 per cent (Sharma and Tripathi, 2019). Trees that are infected at an earlier stage remain stunted and will not produce an economical crop. The virus is grouped into the papaya infecting type (PRSV-P) which infects plants belonging to families Caricaceae, Cucurbitaceae and Chenopodiaceae whereas cucurbit infecting type (PRSV-W) infect plants including families Cucurbitaceae and Chenopodiaceae but not Caricaceae. Both strains are serologically indistinguishable and are transmitted non-persistently by several species of aphids. Efforts have been made to study the incapability of the PRSV-W strain to cause disease infection in papaya. The results of bioassay studies with in vitro transcripts of recombinant PRSV-W with its CP gene replaced with that of a CP gene from PRSV-P demonstrated that the CP gene is not a determinant for infection of papaya (Chen et al., 2001). Similar experiments with PRSV-W containing PRSV-P segments from the region including the NIa gene and a portion of the NIb gene were shown to be required for papaya infection. Mutations in the PRSV-P genome at two amino acid positions in the NIa-Pro region, which differ between PRSV-P and PRSV-W, 2309 (K→D) and 2487 (I→V), demonstrated that these two residues are critical for conferring PRSV pathogenicity in papaya (Chen et al., 2008). However, the exact downstream components which make the papaya plants resistant to PRSV-W are still unknown. Here, the proposed project involves the identification of the protein(s) in papaya which are distinctly acting against the PRSV-P and PRSV -W infection using proteomic approaches. Briefly, the PRSV-P and PRSV-W strains will be isolated, full-length cDNA infectious clones will be developed and a bio-assay will be performed to test its infectivity in papaya as well as in cucumber. Later, the cDNA clones will be tagged with 6X-His tag in the NIa protease region and allowed for infection. Further proceeds with the identification of probable host protein targets of NIa protease by using affinity purification followed by mass spectrometry (AP-MS). The AP-MS results will be analyzed between the proteins which are isolated from papaya plants infected with PRSV-P and PRSV-W. In comparison, the candidate host protein (s) which is distinctly interacting with the NIa protease will be identified and confirmed using yeast two-hybrid assays. The outcome of the proposed investigation will aid in the identification of potential target protein which can be utilized to develop PRSV resistance in papaya.