Cloning, characterization, and expression profile of an insect farnesoic acid O-methyltransferase orthologue from the mud crab Scylla paramamosain Estampador, 1950 (Brachyura: Portunidae): Putative relationship with methyl farnesoate

Abstract

Methyl farnesoate (MF) is a sesquiterpenoid hormone that plays a pivotal role in the regulation of metamorphosis and gonad development in crustaceans. Studies of farnesoic acid O-methyltransferase (FAMeT), which catalyses the transition of farnesoic acid to MF in crustaceans, have long been contradictory. We obtained a full length of FAMeT cDNA sequence from the portunid crab Scylla paramamosain Estampador, 1950. To distinguish this FAMeT cDNA from the previously reported FAMeT in the mud crab, we name this gene Sp-FAMeT2. The full length of Sp-FAMeT2 was 1,279 bp, with a predicted 762-bp open reading frame (ORF) encoding 253 amino acids with a predicted molecular weight of 28.014 kDa. The protein sequence of Sp-FAMeT2 contained a Methyltransf_FA domain and DUF3421 domain with a DM9 repeat and was thought to be an insect FAMeT orthologue gene. Sp-FAMeT2 mRNA was ubiquitously expressed in all of the detected tissues, with the highest expression in the hepatopancreas, followed by haemolymph and thoracic ganglia. The expression of Sp-FAMeT2 changed significantly during larval and ovary development, and the trends were similar with those of Sp-HMGR, a key enzyme involved in the biosynthesis of MF. Sp-FAMeT2 expression also seemed to have a positive correlation with the role of MF in the growth and metamorphosis of larvae as well as in the development of ovaries. Combined with studies of FAMeT in insects, we hypothesise that Sp-FAMeT2 functions in the MF signaling pathway in an indirect model and thus has a close relationship with larval and ovary development in S. paramamosain.