Capsicum annuum proteinase inhibitor ingestion negatively impacts the growth of sorghum pest Chilo partellus and promotes differential protease expression

Abstract

BackgroundChilo partellus is an important insect pest infesting sorghum and maize. The larvae internalize in the stem, rendering difficulties in pest management. We investigated the effects of Capsicum annuum proteinase inhibitors (CanPIs) on C. partellus larvae by in-vitro and in-vivo experiments.MethodsRecombinant CanPI-7 (with four-Inhibitory Repeat Domains, IRDs), -22 (two-IRDs) and insect proteinase activities were estimated by proteinase assays, dot blot assays and in gel activity assays. Feeding bioassays of lab reared C. partellus with CanPI-7 and -22 were performed. C. partellus proteinase gene expression was done by RT-PCR. In-silico structure prediction of proteinases and CanPI IRDs was carried out, their validation and molecular docking was done for estimating the interaction strength.ResultsLarval proteinases of C. partellus showed higher activity at alkaline pH and expressed few proteinase isoforms. Both CanPIs showed strong inhibition of C. partellus larval proteinases. Feeding bioassays of C. partellus with CanPIs revealed a dose dependent retardation of larval growth, reduction of pupal mass and fecundity, while larval and pupal periods increased significantly. Ingestion of CanPIs resulted in differential up-regulation of C. partellus proteinase isoforms, which were sensitive to CanPI-7 but were insensitive to CanPI-22. In-silico interaction studies indicated the strong interaction of IRD-9 (of CanPI-22) with Chilo proteinases tested.ConclusionsOf the two PIs tested, CanPI-7 prevents induction of inhibitor insensitive proteinases in C. partellus so it can be explored for developing C. partellus tolerance in sorghum.General significanceIngestion of CanPIs, effectively retards C. partellus growth; while differentially regulating the proteinases.

Evaluating the pesticidal impact of plant protease inhibitors: lethal weaponry in the co‐evolutionary battle

“…Several attempts have been made successfully to introduce foreign PIs and overexpress the native PIs in plants (Table 3). 66,73–93 This would facilitate the selection of appropriate combination of PIs to achieve maximum protection against pest and pathogens. About two decades ago, PIs were popularised as a key weapon to combat insect herbivory 101 .…”

“…The cowpea TI gene ( CpTI ) was first PI (Bowman–Birk type) to be overexpressed in tobacco and later was inserted in other plant genomes such as sweet potato, potato cotton, rice, cabbage, strawberry and pigeon pea to improve insect resistance (Table 3). 66,73–93 …”

“…Evolutionary conflict is reflected by insect insensitivity and efficient avoidance, causing commercial failure of insect‐resistant transgenic crops 103,140 . Capsicum annuum (Pin II type) CanPI‐7 was demonstrated to be a dose‐dependent inhibitor against Chilo partellus (pest of maize and sorghum) 77 . CanPI‐7 is more active against Helicoverpa armigera neonates, in contrast to the third‐instar larvae.…”