Lipophorin receptor regulates the cuticular hydrocarbon accumulation and adult fecundity of the pea aphid Acyrthosiphon pisum

Abstract

Cuticular hydrocarbons form a barrier that protects terrestrial insects from water loss via the epicuticle. Lipophorin loads and transports lipids, including hydrocarbons, from one tissue to another. In some insects, the lipophorin receptor (LpR), which binds to lipophorin and accepts its lipid cargo, is essential for female fecundity because it mediates the incorporation of lipophorin by developing oocytes. However, it is unclear whether LpR is involved in the accumulation of cuticular hydrocarbons and its precise role in aphid reproduction remains unknown. We herein present the results of our molecular characterization, phylogenetic analysis, and functional annotation of the pea aphid (Acyrthosiphon pisum) LpR gene (ApLpR). This gene was transcribed throughout the A. pisum life cycle, but especially during the embryonic stage and in the abdominal cuticle. Furthermore, we optimized the RHA interference (RNAi) parameters by determining the ideal dose and duration for gene silencing in the pea aphid. We observed that the RNAibased ApLpR suppression significantly decreased the internal and cuticular hydrocarbon contents as well as adult fecundity. Additionally, a deficiency in cuticular hydrocarbons increased the susceptibility of aphids to desiccation stress, with decreased survival rates under simulated drought conditions. Moreover, ApLpR expression levels significantly increased in response to the desiccation treatment. These results confirm that ApLpR is involved in transporting hydrocarbons and protecting aphids from desiccation stress. Furthermore, this gene is vital for aphid reproduction. Therefore, the ApLpR gene of A. pisum may be a novel RNAi target relevant for insect pest management.

Downregulation of NADPH‐cytochrome P450 reductase via RNA interference increases the susceptibility of Acyrthosiphon pisum to desiccation and insecticides

“…qRT‐PCR was performed using SYBR ® Premix Ex Taq TM II mix (TaKaRa Bio) on an ABI 7300 Real‐Time PCR System (Bio‐Rad, Hercules, CA). The qRT‐PCR reaction system and procedure, as well as the reference gene (ribosomal protein S20; NM_001162819.2) and calculation method for the relative expression of target genes were as described in our previous study (Qiao et al ., 2021). The qRT‐PCR primer sequences and their amplification efficiencies are shown in Table S1.…”

“…A 306 bp fragment of the target gene ApCPR (XM_001945277.5) was amplified using the PCR reaction system following the procedures described in our previous study (Qiao et al ., 2021). Lymphotoxin A of Mus musculus ( Muslta ; XM_006536550.2) was selected as the control gene (Chen et al ., 2016).…”

“…A 193 bp coding‐fragment of Muslta was used to synthesize ds Muslta as a negative control. dsRNA delivery was performed via microinjection as described in our previous study (Qiao et al ., 2021).…”

“…The purification and preparation steps for the GC‐MS analysis were consistent with the aforementioned steps for CHCs. GC‐MS was used to quantify the HCs as described previously (Qiao et al ., 2021).…”

“…Moreover, CHCs play a crucial role in protecting insects by decreasing cuticular permeability (Feingold & Elias, 2014; Balabanidou et al ., 2018; Chen et al ., 2020; Yang et al ., 2020). Insect CHCs comprise straight or methyl‐branched long‐chain alkanes and alkenes (Lockey, 1988; Martin & Drijfhout, 2009; Blomquist, 2010; Geiselhardt et al ., 2011; Arcaz et al ., 2016; Pei et al ., 2019; Chen et al ., 2020; Qiao et al ., 2021), which are synthesized in specialized secretory cells known as oenocytes (Schal et al ., 1998; Fan et al ., 2003; Makki et al ., 2014) and transported to internal organs and insect epicuticles via a high‐density lipoprotein called lipophorin (Haruhito & Haruo, 1982; Schal et al ., 1998, 2001; Fan et al ., 2004). The CHC biosynthesis pathway in insects comprises 4 stages: precursor synthesis catalyzed by fatty acid synthases; desaturation and elongation catalyzed by desaturases and elongases, respectively; reduction catalyzed by reductases; and decarboxylation catalyzed by CYP4Gs (Qiu et al ., 2012; Chung et al ., 2014; Chung & Carroll, 2015; Grigoraki et al ., 2020).…”