Constitutive and phloem specific expression of Allium sativum leaf agglutinin (ASAL) to engineer aphid (Lipaphis erysimi) resistance in transgenic Indian mustard (Brassica juncea)

Lipaphis erysimi, commonly known as mustard aphid is a seriously damaging pest of important oilseed crop, Brassica juncea. In previous study we reported using artificial diet bioassay that Allium sativum leaf lectin, ASAL shows insecticidal activity against sap sucking L. erysimi. A gut receptor protein having binding affinity to ASAL was purified from L. erysimi. The receptor protein was further identified as a SymL, playing role in aphid mediated virus transmission. To develop resistance against the above pest, ASAL had been expressed in mustard both in constitutive and phloem tissue specific manner. Stable integration and inheritance of ASAL gene has been shown through Southern hybridization. Expression of ASAL has been confirmed in T0 and T1 plants through northern and western blot analyses. The segregation pattern of ASAL transgene and hygromycin selection marker gene were observed in T1 progenies which followed the 3:1 Mendelian ratio. The phloem tissue specific expression of ASAL gene driven by rice sucrose synthase promoter (RSs-1) has also been monitored by immunohistochemical analysis of mature stem and petiole sections. In-planta bioassays on T0 plants and their progenies exhibited the efficacy of expressed ASAL to reduce the survival and fecundity of L. erysimi. This is the first report showing sustainable resistance in transgenic B. juncea with ASAL gene against the target pest, mustard aphid.