Transcriptional Analysis of The Adaptive Digestive System of The Migratory Locust in Response to Plant Defensive Protease Inhibitors.

Jornt Spit,Liesbet Badisco,Michiel Holtof,Lucia Vergauwen,Jozef Vanden Broeck,Dries Knapen,Elise Vogel

doi:10.1038/srep32460

Abstract

Herbivorous insects evolved adaptive mechanisms to compensate for the presence of plant defensive protease inhibitors (PI) in their food. The underlying regulatory mechanisms of these compensatory responses remain largely elusive. In the current study, we investigated the initiation of this adaptive response in the migratory locust, Locusta migratoria, via microarray analysis of gut tissues. Four hours after dietary uptake of PIs, 114 and 150 transcripts were respectively found up- or downregulated. The results suggest a quick trade-off between compensating for potential loss of digestive activity on the one hand, and stress tolerance, defense, and structural integrity of the gut on the other hand. We additionally addressed the role of a group of related upregulated hexamerin-like proteins in the PI-induced response. Simultaneous knockdown of corresponding transcripts by means of RNA interference resulted in a reduced capacity of the locust nymphs to cope with the effects of PI. Moreover, since insect hexamerins have been shown to bind Juvenile Hormone (JH), we also investigated the effect of JH on the proteolytic digestion in L. migratoria. Our results indicate that JH has a stimulatory effect on the expression of three homologous chymotrypsin genes, while knocking down the JH receptor (methoprene tolerant) led to opposite effects.

Highlights

Several important pest insects have evolved mechanisms to compensate for the antimetabolic effects of protease inhibitors (PI), with attenuation, or a complete lack of developmental defects as a result[5]
Our previous research demonstrated that an increase in proteolytic enzyme expression could already be observed four hours after the dietary uptake of soybean Bowman Birk (SBBI) and SBTi (1%) in L. migratoria
We investigated large scale transcriptional changes that occur in the midgut and gastric caeca of fifth instar L. migratoria nymphs, four hours after dietary uptake of SBBI and soybean trypsin inhibitors (SBTI)

Summary

Introduction

Several important pest insects have evolved mechanisms to compensate for the antimetabolic effects of PI, with attenuation, or a complete lack of developmental defects as a result[5]. We previously have shown that L. migratoria possesses a clear PI-based compensatory response[13] It responds to the dietary uptake of soybean Bowman Birk (SBBI) and soybean trypsin inhibitors (SBTI) by inducing the expression of serine proteases active in the digestive system, while no effect on larval development could be observed[13]. One other study performed in the Colorado potato beetle, Leptinotarsa decemlineata, demonstrated an induced expression of several JHBPs after feeding on potato plants with induced defences[16] These findings could suggest a more general role for JHBPs or JH in the regulation of the digestive process in insects. We were able to demonstrate a stimulatory effect of JH signalling on a specific group of serine proteases, further hinting towards a conserved role for this hormone in the regulation of digestion

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Results

Conclusion