Nicotiana tabacum agglutinin is active against Lepidopteran pest insects

A jasmonate-inducible lectin called Nicotiana tabacum agglutinin or NICTABA was found in tobacco (Nicotiana tabacum cv Samsun) leaves. Since NICTABA expression is also induced after insect herbivory, a role in the defence response of tobacco was suggested. In this report, a detailed analysis was made of the entomotoxic properties of NICTABA using different transgenic approaches. First, purified NICTABA was shown to be strongly resistant to proteolytic degradation by enzymes present in the Lepidopteran midgut. To address the question of whether NICTABA is also active against Lepidopteran larvae, transgenic N. tabacum plants that silence endogenous NICTABA expression were constructed using RNA interference. Feeding experiments with these transgenic N. tabacum plants demonstrated that silencing of NICTABA expression enhances the larval performance of the generalist pest insect Spodoptera littoralis. In a second transgenic approach, NICTABA was ectopically expressed in the wild diploid tobacco Nicotiana attenuata, a species that lacks a functional NICTABA gene. When these transgenic N. attenuata plants were used in feeding experiments with S. littoralis larvae, a clear reduction in mass gain and significantly slower development were observed. In addition, feeding experiments with the Solanaceae specialist, Manduca sexta, provided further evidence that NICTABA exerts clear entomotoxic effects on Lepidopteran larvae.