4 DISCUSSIONS
C. japonica is a kind of forestry pest and has been evaluated for
its potential medical value (Chen et al. , 2022). It is meaning to
turn this pest, which threatens the development of economic forestry,
into a useful resource through in-depth study of its genetic and
physiological characteristics, which may help us to promote efficient
management solutions and develop a massive rearing technique for
obtaining abundant population of C. japonica as economic
resources. In this study, we obtained high-quality genome at chromosome
level. With the combination of Illumina NovaSeq, PacBio Sequel Ⅱ and
Hi-C technology, we obtained that C. japonica has 31 chromosomes,
and the genome size is 584.5 MB.
To annotate the genes involved to diapause, we manually annotated the
existence of six potential diapause related genes in C. japonica(DH-PBAN ,PTTH, cry1 , cry2 , per and tim ). The absence
of per in C. japonica attracted our attention. It is not a
unique event, although the DNA sequence of clock genes have been
well-conserved. It was also not found of per in Cydia
pomonella and Anoplophora glabripennis (Cao et al. ,
2021). The absence of cry2 in Drosophila and the absence
of cry1 in Tribolium castaneum and Apis mellifera has been
reported (Yuan et al. , 2007) (Sandrelli et al. , 2008).per is not a necessary gene for these Lepidoptera insects and may
have been lost in the process of evolution. per and timare transcribed promoted by CLK and CYC in the nucleus and translated
into proteins in the cytoplasm. At the same time, the concentration of
PER and TIM will also reduce the level of CLK and CYC by negative
feedback, thus reducing the transcription of per and tim(Tomioka and Matsumoto, no date). However, CRY2 is likely more important
negative regulator for transcription of CLK and CYC in some insects and
can degrade by light. Therefore, it could be existing some complementary
factor of PER in function of circadian regulation pathway. Although,per gene has occurred mutation in evolution, some non-PER insect
can develop normally and adapt rhythmic change regularly. S.
ricini has the same number of diapause-related genes (in this study)
with C. japonica and both absence of per . However,A. pernyi and A. yamamai have different related-diapause
gene with two formers. Based on their phylogenetic relationship (Figure
4), it may occur some evolutionary events in rhythmic system. In someper -null flies, they also can into diapause, that suggests per
may not involve in initiating by photoperiodic diapause(Saunders,
Henrich and Gilbert, 1989).
Genes related to circadian clock are usually expressed in neurosecretory
cells in the brain, and these regions also regulate diapause-related
hormones gene expression(Meuti and Denlinger, 2013). In non-diapause
mutation files of Chymomyza costata , there is a mutation in 5’
leader sequence of tim gene, which suggested TIM plays an
important role in it regulation for diapause (Pavelka, Shimada and
Kostal, 2003). When per and cry2 were knocked down in bean
bug, Riptortus pedestris , it caused the ovarian development of
female adults which should have entered diapause in short photoperiod.
Similarly, RNA interference (RNAi) was used to interrupt expression of
per and cry2 in male adult, which can avoid diapause (Ikeno, Numata and
Goto, 2011). Research above indicate that circadian genes can involve in
photoperiodic diapause. Hence, for the development of diapause related
research of C. japonica , it is important to understand the
pathway patterns of circadian genes and diapause-related genes in the
genome of the species.
Diapause of resources insects and nature enemies is an important but
unaddressed issue. It is a key technical barrier restricting the
quantity of products and industrial development in the utilization of
resource insects. For example, in the silk industry, the diapause of
silkworm will affect the quality and yield of silk. Therefore, the
diapause removal of silkworm and its related regulation mechanism have
been studied very deeply. If the female adult experiences high
temperature during the embryonic period, it will produce diapause eggs
(Tsuchiya et al ., 2020). In biological control, the simple
acquisition of alternative hosts is the key to the large-scale
propagation of natural enemy insects. Diapause also exists in the
industrial production of A. pernyi , an important intermediate
host of natural enemies such as Trichogrammatidae and Eupelmidae.
However, the commercial A. pernyi has been cultivated, there are
still some limitations in quality and yield. Not only Lepidoptera, but
other natural enemy insects will also be refrigerated to facilitate
storage and transportation in biological control, which will cause
diapause. The common problem is that the natural enemy insects take a
long time to remove diapause, which will affect their control effect on
pests. The cocoon of pupa of C. japonica can used to produce
natural material. So, it has great potential to explore as a resource
insect for its medical value. It is meaningful to know how to regulate
the diapause of C. japonica.
The evolution and fluctuation of expression of the gene according to
diapause usually caused by environment. However, the critical values of
natural conditions for diapause of C. japonica , such as
photoperiod and temperature, have not been explored clearly. Therefore,
we will quantify the impact of these abiotic factors on diapause and to
explore the gene foundations according to biological changes. The
expression of each gene in the C. japonica still needs to be
explored clearly to better carry out the follow-up verification
experiment.
In summary, we firstly reported a high-quality chromosome scale genome
of C. japonica and discuss the evolution of diapause related
genes. It will provide a valuable database for the future study around
resource insect and biomedical materials development.