IDENTIFICATION AND HORMONE INDUCTION OF PUTATIVE CHITIN SYNTHASE GENES AND SPLICE VARIANTS IN Leptinotarsa decemlineata (SAY)

Abstract

Chitin synthase (ChS) plays a critical role in chitin synthesis and excretion. In this study, two ChS genes (LdChSA and LdChSB) were identified in Leptinotarsa decemlineata. LdChSA contains two splicing variants, LdChSAa and LdChSAb. Within the first, second, and third larval instars, the mRNA levels of LdChSAa, LdChSAb, and LdChSB coincide with the peaks of circulating 20-hydroxyecdysone (20E) and juvenile hormone (JH). In vitro culture of midguts and an in vivo bioassay revealed that 20E and an ecdysteroid agonist halofenozide stimulated the expression of the three LdChSs. Conversely, a reduction of 20E by RNA interference (RNAi) of an ecdysteroidogenesis gene LdSHD repressed the expression of these LdChSs, and ingestion of halofenozide by LdSHD RNAi larvae rescued the repression. Moreover, disruption of 20E signaling by RNAi of LdEcR, LdE75, LdHR3, and LdFTZ-F1 reduced the expression levels of these genes. Similarly, in vitro culture and an in vivo bioassay showed that exogenous JH and a JH analog methoprene activated the expression of the three LdChSs, whereas a decrease in JH by RNAi of a JH biosynthesis gene LdJHAMT downregulated these LdChSs. It seems that JH upregulates LdChSs at the early stage of each instar, whereas a 20E pulse triggers the transcription of LdChSs during molting in L. decemlineata.

RNA interference of chitin synthase genes inhibits chitin biosynthesis and affects larval performance in Leptinotarsa decemlineata (Say)

“…Moreover, LdChSA contains two splicing variants, LdChSAa and LdChSAb 26. In the present paper, we found that RNAi of both LdChSA isoforms, or each of LdChSAa , LdChSAb or LdChSB severely affected larval growth, caused larval lethality, and impaired larval-larval molting, larval-pupal ecdysis and adult emergence.…”

“…Furthermore, chitin is absent in plants and vertebrates. All these results indicate that ChS provides an important target for a potential pest control strategy through RNAi 18, 25, 26.…”

“…LdChSA has two splicing variants, LdChSAa and LdChSAb 26. It is well known that RNAi-mediated knockdown of ChS dramatically affects survival, ecdysis, oviposition and egg hatching in different insect species 7, 8, 17-20.…”

“…Conversely, this process is absent in vertebrates and plants 18, 25, 26. It is accordingly considered that ChS presents an attractive target for combating insect pests and fungi-born diseases.…”

Silencing chitin deacetylase 2 impairs larval–pupal and pupal–adult molts in Leptinotarsa decemlineata

“…Fortunately, dietary introduction of bacterially expressed double‐stranded RNAs (dsRNAs) is able to effectively knock down target genes in L. decemlineata (Sun et al ., ; Meng et al ., ; ; Xu et al ., ). Moreover, chitin is absent in vertebrates, and chitin biosynthesis enzymes have been confirmed to be potential targets for novel insecticide development (Shi et al ., ; ). These prompt us to carry out a functional analysis of CDA2 in L. decemlineata larvae and to estimate its potential effect on the larvae.…”