The Function Of Progesterone-mediated Oocyte Maturation Pathway In The Reproductive Model Switch Of Cotton Aphid Aphis Gossypii

The cotton aphid (Aphis gossypii Glover), an important agricultural insect pest, is able to reproduce asexually and sexually upon environmental change. During spring and summer, the cotton aphid reproduces asexually via viviparous parthenogenesis. In the fall, the parthenogenetic females produce gynoparae that produce sexual females (oviparous females). The sexual females mate with the males and lay overwintering eggs. Although the holocyclic life cycle and reproductive mode transition (or reproductive polyphenism) of the cotton aphid have been characterized, litter is known about the underlying molecular mechanisms. The pea aphid, Acyrthosiphon pisum has been used as a model for studies on reproductive polyphenism. Different from the pea aphid, the cotton aphid is a host-alternating species. In addition, the cotton aphid has the unique form of gynopara. In an effort to reveal the molecular mechanisms of reproductive mode switch in the cotton aphid, our laboratory has performed RNA-seq to explore the differential gene expression profiles among parthenogenetic females, gynoparae and sexual females. GO category and KEGG pathway analysis suggest that the multiple signal pathways including phototransduction, progesterone-mediated oocyte maturation, endocrine regulation and cuticle composition are likely to be involved in the regulation of reproductive mode transition in the cotton aphid.In this dissertation research, the progesterone-mediated oocyte maturation pathway and the phototransduction pathway were selected for further studies. Validation with qRT-PCR was conducted for bubl、ccna2、polo、plkl and mad2 in the progesterone-mediated oocyte maturation pathway, showing that the expression levels of bubl、ccna2 and polo were higher in parthenogenetic females than that in gynoparae. Knockdown of bub1 or ccna2 via dsRNA injection had an apparent impact on ovarian development of parthenogenetic females. However, whether depletion of bubl or ccna2 has an effect on the transition from parthenogenetic females to gynoparae is undetermined. qRT-PCR was also performed for the developmental expression profiles of ninac、opsin、arr2、 GNB2、Trp and ANA in the phototransduction pathway during gynopara development, which showed that the expression of ninac, opsin, arr2 and GNB2 was significantly increased at 4th instar nymphs of gynoparae.The cotton aphid is characterized by its tiny body size, thin cuticle and rich body fluid. RNAi in the cotton aphid, particularly the comparison of dsRNA delivery methods are less explored. In this dissertation study, dsRNA injection and ingestion were compared, including injection sites, injection doses, ingestion doses, tissue uptake, and RNAi efficiency. The advantages and disadvantages of these two delivery methods are discussed. For dsRNA injection, the optimal site is the conjunctive between the mesothorax and metathorax, and the optimal dose is 10 ng. For dsRNA ingestion, the optimal dose is 400 ng/μl. When fluorescent Cy3-siRNA was injected or ingested, the fluorescent signal was detectable in the ovary and gut of cotton aphids.