Identification of Albizia lebbeck seed coat chitin-binding vicilins (7S globulins) with high toxicity to the larvae of the bruchid Callosobruchus maculatus

Abstract

Seed coat is a specialized maternal tissue that interfaces the embryo and the external environment during embryogenesis, dormancy and germination. In addition, it is the first defensive barrier against penetration by pathogens and herbivores. Here we show that Albizia lebbeck seed coat dramatically compromises the oviposition, eclosion and development of the bruchid Callosobruchus maculatus. Dietary supplementation of bruchid larvae with A. lebbeck seed coat flour causes severe weight loss and reduces survival. By means of protein purification, mass spectrometry and bioinformatic analyses, we show that chitinbinding vicilins are the main source of A. lebbeck tegumental toxicity to C. maculatus. At concentrations as low as 0.1%, A. lebbeck vicilins reduce larval mass from 8.1 ± 1.7 (mass of control larvae) to 1.8 ± 0.5 mg, which corresponds to a decrease of 78%. Seed coat toxicity constitutes an efficient defense mechanism, hindering insect predation and preventing embryo damage. We hypothesize that A. lebbeck vicilins are good candidates for the genetic transformation of crop legumes to enhance resistance to bruchid predation.

Soybean seed coat chitinase as a defense protein against the stored product pest Callosobruchus maculatus

“…To test the effects of the chitinase‐rich fraction on larval development, an artificial seed system was used . Different concentrations of the fraction (0.1, 0.5 and 1.0% w/w) were mixed with V. unguiculata cotyledonary flour in order to make up 400 mg.…”

“…Although chitinase has been detected in the mature soybean seed coat, its participation in seed defense mechanisms has not yet been shown. The seed coat is an external tissue that protects the seed and regulates water absorption during germination . Previous works have shown that proteins from the seed coat prevent insect attacks, such as those by C. maculatus, the most important pest of cowpea ( Vigna unguiculata ) seeds.…”

“…Previous works have shown that proteins from the seed coat prevent insect attacks, such as those by C. maculatus, the most important pest of cowpea ( Vigna unguiculata ) seeds. Attack by this bruchid causes significant economic losses in stored seeds, decreasing their commercial and nutritional values and germination potential . In this work, we studied the efficiency of a soybean seed coat chitinase as a defense protein against the insect Callosobruchus maculatus , when present in an artificial seed coat or cotyledons.…”

“…The seed coat is an external tissue that protects the seed and regulates water absorption during germination. [12][13][14] Previous works have shown that proteins from the seed coat prevent insect attacks, such as those by C. maculatus, the most important pest of cowpea (Vigna unguiculata) seeds. Attack by this bruchid causes significant economic losses in stored seeds, decreasing their commercial and nutritional values and germination potential.…”

“…Attack by this bruchid causes significant economic losses in stored seeds, decreasing their commercial and nutritional values and germination potential. [12][13][14] In this work, we studied the efficiency of a soybean seed coat chitinase as a defense protein against the insect Callosobruchus maculatus, when present in an artificial seed coat or cotyledons.…”