CHARACTERIZATION AND FUNCTIONAL STUDY OF A PUTATIVE JUVENILE HORMONE DIOL KINASE IN THE COLORADO POTATO BEETLE Leptinotarsa decemlineata (Say)

Abstract

Juvenile hormone diol kinase (JHDK) is an enzyme involved in JH degradation. In the present article, a putative JHDK cDNA (LdJHDK) was cloned from the Colorado potato beetle Leptinotarsa decemlineata. The cDNA consists of 814 bp, containing a 555 bp open reading frame encoding a 184 amino acid protein. LdJHDK reveals a high degree of identity to the previously reported insect JHDKs. It possesses three conserved purine nucleotide-binding elements, and contains three EF-hand motifs (helix-loop-helix structural domains). LdJHDK mRNA was mainly detected in hindgut and Malpighian tubules. Besides, a trace amount of LdJHDK mRNA was also found in thoracic muscles, brain-corpora cardiaca-corpora allata complex, foregut, midgut, ventral ganglia, fat body, epidermis, and hemocytes. Moreover, LdJHDK was expressed throughout all developmental stages. Within the first, second, and third larval instar, the expression levels of LdJHDK were higher just before and right after the molt, and were lower in the intermediate instar. In the fourth larval instar, the highest peak of LdJHDK occurred 56 h after ecdysis. Ingestion of double-stranded RNA (dsRNA) against LdJHDK successfully knocked down the target gene, increased JH titer, and significantly upregulated LdKr-h1 mRNA level. Knockdown of LdJHDK significantly impaired adult emergence. Thus, we provide a line of experimental evidence in L. decemlineata to support that LdJHDK encodes function protein involved in JH degradation.

Identification and Characterization of Three Juvenile Hormone Genes fromBactrocera dorsalis(Diptera: Tephritidae)

“…There were 3 conserved sequence elements responsible for purine nucleotide binding and 3 elongation factor (EF)-hand motifs in both dSCP2 and GTP-binding proteins (Maxwell et al 2002a,b). Several JHDK cDNAs have been identified from insect species, such as Danaus plexippus L. (Lepidoptera: Nymphalidae), Plutella xylostella L. (Lepidoptera: Plutellidae), and B. mori (Li et al 2005), Ostrinia furnacalis Guenée (Lepidoptera: Crambidae) (Feng & Zhai 2011), Spodoptera litura F. (Lepidoptera: Noctuidae) (Zeng et al 2015), and L. decemlineata (Fu et al 2015). The recombinant Bm-JHDK of B. mori in Sf9 cells using a baculovirus system converted 10S-JH diol to form JHdp, suggesting its enzymatic function in JH regulation (Li et al 2005).…”

“…The recombinant Bm-JHDK of B. mori in Sf9 cells using a baculovirus system converted 10S-JH diol to form JHdp, suggesting its enzymatic function in JH regulation (Li et al 2005). In L. decemlineata, knockdown of LdJHDK significantly increased the hemolymph JH titer and negatively affected adult emergence (Fu et al 2015).…”

“…Previous studies sought to develop new insect pest management strategies by targeting vital genes that function mainly during development (Baum et al 2007;Yang et al 2013a). The activities of JH-metabolizing enzymes are likely to be critical for successful functional regulation of JH in insect growth and development (Yang et al 2011;Fu et al 2015;Lü et al 2015). Bactrocera dorsalis is a typical holometabolous insect that undergoes dramatic morphological changes during development from egg to adult.…”

Hormonal signaling cascades required for phototaxis switch in wanderingLeptinotarsa decemlineatalarvae

“…At the wandering stage, JH titer obviously decreased [41], and the expression of JH degradation genes were activated [39]. Here we found that ingestion of JH (Fig 2F), or knockdown of an allatostatin gene ( AS-C ) [41] or either of two JH degradation genes (JH epoxide hydrolase, JHEH1 ; JH diol kinase, JHDK ) [35, 39] to delay JH decrease significantly reduced light avoidance (Fig 2G and S1E-G Fig) and postponed the occurrence of wandering (S2 Table); whereas knockdown of a JH biosynthesis gene (JH acid methyl transferase, JHAMT ) [34] and a JH receptor gene (methoprene-tolerant, Met ) to prematurely reduce JH signal enhanced light avoidance (Fig 2H and S1H, I Fig) and accelerated the onset of wandering (S2 Table). It is clear that JH signal inhibits the premature switch of light preference and the early onset of wandering.…”

Validating the potential of double-stranded RNA targeting Colorado potato beetlemeshgene in laboratory and field trials

“…This makes CPB an excellent candidate for pest management using dsRNAs, which was first recognized in a study by Baum et al (2007) that has also identified several RNAi targets. This was followed by studies that identified novel effective target genes in CPB (Zhu et al 2011Zhou et al 2013;Wan et al 2014;Meng et al 2015Meng et al , 2018Lü et al 2015;Fu et al 2015Fu et al , 2016Shi et al 2016b, a;Guo et al 2016;Xu et al 2018). In western corn rootworm, Hu et al (2016) identified another target gene -mesh (alternatively named dvssj2) which encodes a smooth septate junction protein important for structural integrity of the midgut epithelium.…”