Molecular Evolution Of Argonaute Protein Genes Of Seven Fig Wasps

Argonaute proteins are associated with the different classes of small RNAs,and indispensable in small RNA-mediated regulatory pathways.Argonaute proteins are extremely conservative and have been identified in diverse organisms from plants and animals.Via binding to small RNA,Argonaute proteins play important roles in gene regulation.They can act as endonuclease,are the core component of RNA-induced silencing complex(RISC)and play vital roles in RNA inference(RNAi).Argonaute proteins can also participate in epigenetic regulation,and the regulation of transcription and translation.These essential regulation functions thus make the Argonaute proteins important in the embryonic development processes of organisms.By far,no related research of Argonaute proteins has been reported in fig wasps(Hymenoptera: Chalcidoidea).In this study,I am interested in the evolutionary relationships of Argonaute genes among different fig wasp species and the selection pressure subjected to all the Argonaute genes.In my study,first,I designed primers for RT-PCR(reverse transcription Polymerase Chain Reaction)to get the conservative fragments of Argonaute genes;second,based on the conservative fragments,I designed primers for hiTAIL-PCR(High-efficient thermal asymmetric interlaced PCR)to get longer Argonaute gene sequences.For species with genomic sequence and / or transcriptome data,such as Ceratosolen solmsi and Walkerella sp.,I also obtained all the argonaute gene sequences by manual annotation,exons assembling,and experimentally validation.In summary,I obtained sixteen argonaute gene sequences from seven different fig wasps,based on which,I used MEGA6.0 software to construct gene trees.Then I used PAML program to test selection pressure by using the site model.The results were as follows: 1)All the fig wasp species had two to four Argonaute genes,with members encoding proteins from the AGO subfamily and PIWI subfamily,except that the fig-pollinating wasp C.solmsi lacked the PIWI subfamily protein gene and had only the AGO subfamily protein genes of Ago2 and Ago2-like.2)In the analyses of selection pressure,no positive selection site was found based on the comparisons between models of M0/M3,M1/M2,and M7/M8;each branch in the gene tree was under purifying selection.The conservation of the argonaute proteins was further confirmed by the prediction of the conserved domain of the all Argonaute protein sequences.Nevertherless,the lack of the coding gene of PIWI subfamily protein for C.solmsi is still an unresolved question.