Knockdown of cadherin genes decreases susceptibility of Chilo suppressalis larvae to Bacillus thuringiensis produced Crystal toxins

Abstract

The striped rice stem borer, Chilo suppressalis Walker, is one of the most destructive rice pests in Asia. Insecticidal crystal proteins (Cry toxins) produced by Bacillus thuringiensis are widely used as biopesticides or in developing transgenic crops for pest management. In this study, we tested the involvement of two newly cloned C. suppressalis cadherins (CsCAD3 and CsCAD4) in the toxicity of Cry1Ab/Ac, Cry2Aa and Cry1Ca. Our results showed that CsCAD4 was expressed highest in the midgut, whereas CsCAD3 was expressed highest in the epidermis. The feeding of double-stranded RNA specific to CsCAD3 and CsCAD4 respectively significantly suppressed the expressions of target gene. The knockdown of CsCAD3 significantly reduced the mortality of larvae to Cry1Ab/Ac, whereas knockdown of CsCAD4 significantly decreased the larval susceptibility to Cry2Aa. In contrast, reduced expressions of CsCAD3 or CsCAD4 were not interacted with larval susceptibility to Cry1Ca. Our results suggest that CsCAD3 and CsCAD4 function in Cry toxin toxicity and these findings will help us to better understand the action mechanism of Cry toxins in C. suppressalis.

The induced knockdown of GmCAD receptor protein encoding gene in Galleria mellonella decreased the insect susceptibility to a Photorhabdus akhurstii oral toxin

“…Furthermore, GmCAD was most abundantly expressed in the midgut tissues compared to other body parts such as Malpighian tubule, foregut, hindgut, head, and fat body. A similar expression patterns of CAD was detected in other lepidopteran insects [ 30 , 32–35 ]. Incidentally, we found that the G. mellonella fourth-instar stage was most vulnerable to P. akhurstii TcaB intoxication and TcaB catalytic activity in the midgut epithelium [ 21 , 22 ].…”

“…Fourteen cadherin repeats (CRs) were predicted in the extracellular domain. Interestingly, among lepidopteran CADs, a number of CRs ( B. mori – 9, O. nubilalis, S. exigua, Pectinophora gossypiella, Heliothis virescens – 11, Helicoverpa armigera, M. sexta – 12, C. suppressalis – 14) vary considerably [ 29 , 30 ], indicating its species-specific conservation. Fifty-four CAD sequences from different insect species were used to construct a maximum likelihood method-based phylogenetic tree, which showed that lepidopteran CAD sequences are highly conserved as they form a distinct clade that diverges from hymenopteran, isopteran, coleopteran and hemipteran clades.…”

“…Subsequently, the susceptibility of dsRNA-treated insects to TcaB toxin was markedly reduced as revealed by the mortality data. Similar RNAi silencing of CAD transcription in a number of lepidopteran insects also led to reduced sensitivity to Cry toxins, implying that CAD is a functional receptor of gut-active toxins [ 29 , 30 , 32–35 ]. Expression interference of GmCAD did not cause any unintended off-target effect as GmCAD suppression did not affect pupal and adult development of G. mellonella in our study.…”

Molecular characterization and functional analysis of Cry toxin receptor‐like genes from the model insect Galleria mellonella

“…14 CRs are predicted in the extracellular domain. , 11, 11, 11, 11, 12, 12 and 14 CRs, respectively (Fabrick & Wu, 2015;Zhou et al, 2020). Our motif conservation analysis indicated that motif numbers and location varied within the CAD homologues from order Lepidoptera.…”

“…The number of CRs varies greatly across the lepidopteran CADs suggesting a species‐specific conservation. For example, B. mori , O. nubilalis , S. exigua , P. gossypiella , H. virescens , H. armigera , M. sexta and C. suppressalis CADs contain 9, 11, 11, 11, 11, 12, 12 and 14 CRs, respectively (Fabrick & Wu, 2015; Zhou et al, 2020). Our motif conservation analysis indicated that motif numbers and location varied within the CAD homologues from order Lepidoptera.…”