Cyp15F1: A NOVEL CYTOCHROME P450 GENE LINKED TO JUVENILE HORMONE‐DEPENDENT CASTE DIFFERENTION IN THE TERMITE Reticulitermes flavipes

Abstract

Termites are eusocial insects that jointly utilize juvenile hormone (JH), pheromones, and other semiochemicals to regulate caste differentiation and achieve caste homeostasis. Prior EST sequencing from the symbiont-free gut transcriptome of Reticulitermes flavipes unexpectedly revealed a number of unique cytochrome P450 (Cyp) transcripts, including fragments of a Cyp15 family gene (Cyp15F1) with homology to other insect Cyp15s that participate in JH biosynthesis. The present study investigated the role of Cyp15F1 in termite caste polyphenism and specifically tested the hypothesis that it plays a role in JH-dependent caste differentiation. After assembling the full-length Cyp15F1 cDNA sequence, we (i) determined its mRNA tissue expression profile, (ii) investigated mRNA expression changes in response to JH and the caste-regulatory primer pheromones γ-cadinene (CAD) and γ-cadinenal (ALD), and (iii) used RNA interference (RNAi) in combination with caste differentiation bioassays to investigate gene function at the phenotype level. Cyp15F1 has ubiquitous whole-body expression (including gut tissue); is rapidly and sustainably induced from 3 h to 48 h by JH, CAD, and ALD; and functions at least in part by facilitating JH-dependent soldier caste differentiation. These findings provide the second example of a termite caste regulatory gene identified through the use of RNAi, and significantly build upon our understanding of termite caste homeostatic mechanisms. These results also reinforce the concept of environmental caste determination in termites by revealing how primer pheromones, as socioenvironmental factors, can directly influence Cyp15 expression and caste differentiation.

Expressions of juvenile hormone biosynthetic genes during presoldier differentiation in the incipient colony of Zootermopsis nevadensis (Isoptera: Archotermopsidae)

“…These motifs are important for protein conformation (Werck-Reichhart and Feyereisen 2000). Molecular phylogenetic analysis shows that Znev_14299 is most closely related to R. flavipes CYP15A1, which possesses an N-terminal site truncation and pseudogene defect conserved motif (Tarver et al 2012). Based on these results, there is a possibility that Znev_14299 may not have sufficient function for JH biosynthesis in Z. nevadensis.…”

“…However, BLAST database searches were performed using the published CYP15A1 genes from other insect species [R. flavipes (Tarver et al 2012; no. FJ792774), D. punctata (Helvig et al 2004; no.…”

“…CYP15A1, encoding JH epoxidase (Helvig et al 2004), converts methyl farnesoate into JH III, and RNAi resulted in an increase in the level of methyl farnesoate in the corpora allata and a decrease in the JH titer in S. gregaria (Marchal et al 2011). Moreover, knockdown of a JH epoxidase homolog, CYP15F1, by RNAi resulted in a decrease in presoldier differentiation from workers in the rhinotermitid termite Reticulitermes flavipes Kollar (Tarver et al 2012). Consequently, changes in the endogenous JH titer may also be influenced by the expression levels of these genes in Z. nevadensis.…”

Genes Underlying Reproductive Division of Labor in Termites, with Comparisons to Social Hymenoptera

“…The C. secundus Neofem4 gene is similar to the CYP4 genes identified in R. flavipes, but not at a level where they could be considered orthologous (Miura and Scharf, 2011). In addition, as in locusts and cockroaches (Helvig et al, 2004), the last step in the biosynthesis of JHIII from methylfarnesoate seems to be catalyzed by a P450 from the CYP15 family (Tarver et al, 2012). These results imply that P450 genes fulfill important functions during caste differentiation (e.g., soldier development in R. flavipes) as well as social organization (e.g., maintenance of reproductive division of labor in C. secundus).…”

“…In insects, they can be involved in the oxidation of xenobiotic substrates that include secondary plant compounds and insecticides. In addition, a P450 gene has been found to be involved in the biosynthesis of CHCs in cockroaches (Reed et al, 1994;Howard and Blomquist, 2005) and several P450s have been linked to juvenile hormone (JH) production or degradation (Sutherland et al, 1998;Feyereisen, 2012;Tarver et al, 2012). A CYP4C7 gene metabolizes JH in a cockroach and this is linked to ovulation (Sutherland et al, 1998(Sutherland et al, , 2000.…”