Construction of Cowpea (Vigna unguiculata L) cDNA Library and Characterization of an Isolated Lectin Gene

The cDNA library of cowpea was constructed in λ ZAP II vector using poly (A+) RNA from developing seeds of cowpea. Initially, to demonstrate the presence of lectin genes in the cowpea genome, cowpea total genomic DNA was isolated, Southern blotted and hybridized with the heterologous pea lectin cDNA probe. It is observed that there exists a strong homology between lectin genes of cowpea and pea. Hence, cowpea cDNA library was screened for the presence of lectin genes using pea lectin cDNA probe. After primary, secondary and tertiary screening, eight positive clones were obtained. When subcloned into pBluescript, out of these eight clones, only four showed presence of larger cDNA inserts. When the DNA of these positive clones were Southern blotted and hybridized, they showed strong hybridization with the probe DNA. One of the clones was sequenced completely and the nucleotide sequence also showed strong homology with other legume lectin genes.