On the roles of cowpea seed trypsin inhibitor and Griffonia simplicifolia lectin II as resistance factors against insects
Abstract
Seeds of cowpea (Vigna unguiculata (L.) Walp) variety TVu 2027 are resistant to the cowpea weevil (Callosobruchus maculatus (F.)). In TVu2027 seeds, C. maculatus larvae exhibit higher mortality and take longer to develop than in susceptible seeds. It has been claimed (Gatehouse et al. 1979. J. Sci. Food Agric. 30: 948-958) that an elevated level of cowpea trypsin inhibitor (CPTI) confers resistance to TVu2027. To evaluate this hypothesis, we isolated and purified CPTI and determined its impact on cowpea weevil using an artificial seed system. CPTI at dietary levels up to 2.0% (w/w) had no significant effect on mortality of cowpea weevils and caused only slight delays in within-seed developmental times. These results fail to support the hypothesis that CPTI is the basis of resistance in TVu2027. Griffonia simplicifolia II (GS-II), a GlcNAc-specific legume lectin, has insecticidal activity against a number of insect pests including the cowpea weevil. A clone of the GS-II gene was isolated, sequenced and expressed in a bacterial expression system. Recombinant GS-II protein exhibited insecticidal activity against cowpea weevil. These results add support to the hypothesis that genes of the legume lectin gene family encode proteins which can function in defense of legumes against herbivores.
Degree
Ph.D.
Advisors
Murdock, Purdue University.
Subject Area
Molecular biology|Entomology|Ecology
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