Selectable antibiotic resistance marker gene-free transgenic rice harbouring the garlic leaf lectin gene exhibits resistance to sap-sucking planthoppers

Rice, the major food crop of world is severely affected by homopteran sucking pests. We introduced coding sequence of Allium sativum leaf agglutinin, ASAL, in rice cultivar IR64 to develop sustainable resistance against sap-sucking planthoppers as well as eliminated the selectable antibiotic-resistant marker gene hygromycin phosphotransferase (hpt) exploiting cre/lox site-specific recombination system. An expression vector was constructed containing the coding sequence of ASAL, a potent controlling agent against green leafhoppers (GLH, Nephotettix virescens) and brown planthopper (BPH, Nilaparvata lugens). The selectable marker (hpt) gene cassette was cloned within two lox sites of the same vector. Alongside, another vector was developed with chimeric cre recombinase gene cassette. Reciprocal crosses were performed between three single-copy T-0 plants with ASAL- lox-hpt-lox T-DNA and three single-copy T-0 plants with cre-bar T-DNA. Marker gene excisions were detected in T-1 hybrids through hygromycin sensitivity assay. Molecular analysis of T-1 plants exhibited 27.4% recombination efficiency. T-2 progenies of L03C04(1) hybrid parent showed 25% cre negative ASAL-expressing plants. Northern blot, western blot and ELISA showed significant level of ASAL expression in five marker-free T-2 progeny plants. In planta bioassay of GLH and BPH performed on these T-2 progenies exhibited radical reduction in survivability and fecundity compared with the untransformed control plants.