Abstract
Feeding and oviposition deterrents help phytophagous insects to identify host plants. The taste organs of phytophagous insects contain bitter gustatory receptors (GRs). To explore their function, the GRs in Plutella xylostella were analyzed. Through RNA sequencing and qPCR, we detected abundant PxylGr34 transcripts in the larval head and adult antennae. Functional analyses using the Xenopus oocyte expression system and 24 diverse phytochemicals showed that PxylGr34 is tuned to the canonical plant hormones brassinolide (BL) and 24-epibrassinolide (EBL). Electrophysiological analyses revealed that the medial sensilla styloconica of 4th instar larvae are responsive to BL and EBL. Dual-choice bioassays demonstrated that BL inhibits larval feeding and female oviposition. Knock-down of PxylGr34 by RNAi attenuates the taste responses to BL, and abolishes BL-induced feeding inhibition. These results increase our understanding of how herbivorous insects detect compounds that deter feeding and oviposition, and may be useful for designing plant hormone-based pest management strategies.
Highlights
Many phytophagous insects have evolved to select a limited range of host plants
To search for candidate gustatory receptors (GRs) that may be involved in host selection by P. xylostella, we searched for candidates among those that had been annotated in the P. xylostella genome (Engsontia et al, 2014; You et al, 2013), the transcriptome (Yang et al, 2017), and the P. xylostella GRs deposited in GenBank (Supplementary file 1)
We identified the full-length coding sequence of PxylGr34 from our transcriptome data, and found that this gene is highly expressed in the head of the 4th instar larvae and in the antennae of females
Summary
Many phytophagous insects have evolved to select a limited range of host plants. Understanding the ultimate and proximate mechanisms underlying this selection strategy is a crucial issue in the field of insect–plant interactions. Ecology eLife digest Plant-eating insects use their sense of taste to decide where to feed and where to lay their eggs They do this using taste sensors called gustatory receptors which reside in the antennae and legs of adults, and in the mouthparts of larvae. Brassica species as its host plants, and its females pat the leaf surfaces with their antennae before egg laying (Qiu et al, 1998) This behavior may be related to certain chemical components in leaves. Through transcriptome analysis and qPCR, we identified one bitter GR (PxylGr34) highly expressed in the larval head and the adult antennae We functionally analyzed this GR with the Xenopus oocyte expression system and RNAi, and found that PxylGr34 is tuned to BL as a feeding and oviposition deterrent in P. xylostella
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