Recent gene multiplication and evolution of a juvenile hormone esterase-related gene in a lepidopteran pest

Circadian clock genes and photoperiodic diapause in the moth Sesamia nonagrioides

Insects, like most organisms, have an internal circadian clock that oscillates with a daily rhythmicity, and a timing mechanism (photoperiodic clock) that mediates seasonal events, including diapause. It has been argued that there is a connection between the two clocks. The Mediterranean corn stalk borer moth, Sesamia nonagrioides, undergoes facultative diapause governed by photoperiod. To obtain clues to the link between the molecular mechanism of circadian and photoperiod clocks, we cloned and investigated the expression profiles of the clock genes Snper, Sntim, Sncyc and Sncry1 in the aforementioned moth species. Our previous results suggested that these genes might be implicated in the regulation of the diapause programming in S. nonagrioides. Here we studied the expression patterns of these four clock genes in larvae reared under abnormal non-24 h light-dark cycles (L10:D62 and L10:D14:L10:D62) in order to assess whether disruption of circadian clock would have any effect in the photoperiodic regulation of diapause. In the L10:D14:L10:D62 cycle abnormal expression patterns of the Sntim/Sncry1 and Snper/Sncyc, pairs were found, compared to normal 24 h light-dark photoperiods suggesting that individual clock genes are acting independently in the molecular diapause program of S. nonagrioides. Photoperiod therefore appears to be the crucial signal for the regulation of these four genes.

Copy Number Variations of Glycoside Hydrolase 45 Genes in Bursaphelenchus xylophilus and Their Impact on the Pathogenesis of Pine Wilt Disease

The pine wood nematode Bursaphelenchus xylophilus parasitizes millions of pine trees worldwide each year, causing severe wilt and the death of host trees. Glycoside hydrolase 45 genes of B. xylophilus are reported to have been acquired by horizontal gene transfer from fungi and are responsible for cell wall degradation during nematode infection. Previous studies ignored the possibility of copy number variations of such genes. In this study, we determined that two of the glycoside hydrolase 45 genes evolved to maintain multiple copies with distinct expression levels, enabling the nematode to infect a variety of pine hosts. Additionally, tandem repeat variations within coding regions were also detected between different copies of glycoside hydrolase 45 genes that could result in changes in protein sequences and serve as an effective biological marker to detect copy number variations among different B. xylophilus populations. Consequently, we were able to further identify the copy number variations of glycoside hydrolase 45 genes among B. xylophilus strains with different virulence. Our results provide new insights into the pathogenicity of B. xylophilus, provide a practical marker to genotype copy number variations and may aid in population classification.

Molecular evolution of juvenile hormone esterase-like proteins in a socially exchanged fluid

Socially exchanged fluids are a direct means by which an organism can influence conspecifics. It was recently shown that when workers of the carpenter ant Camponotus floridanus feed larval offspring via trophallaxis, they transfer Juvenile Hormone III (JH), a key developmental regulator, as well as paralogs of JH esterase (JHE), an enzyme that catalyzes the hydrolysis of JH. Here we combine proteomic, phylogenetic and selection analyses to investigate the evolution of this esterase subfamily. We show that Camponotus JHE-like proteins have undergone multiple duplications, experienced positive selection, and changed tissue localization to become abundantly and selectively present in trophallactic fluid. The Camponotus trophallactic esterases have maintained their catalytic triads and contain a number of positively-selected amino acid changes distributed throughout the protein, which possibly reflect an adaptation to the highly acidic trophallactic fluid of formicine ants. To determine whether these esterases might regulate larval development, we fed workers with a JHE-specific pharmacological inhibitor to introduce it into the trophallactic network. This inhibitor increased the likelihood of pupation of the larvae reared by these workers, similar to the influence of food supplementation with JH. Together, these findings suggest that JHE-like proteins have evolved a new role in the inter-individual regulation of larval development in the Camponotus genus.