Cloning, expression and functional analysis of farnesoic acid O-methyltransferase (FAMeT) in the mud crab, Scylla paramamosain

Abstract

Farnesoic acid O-methyltransferase (FAMeT) is the enzyme that catalyses methylation of farnesoic acid (FA) to produce isoprenoid methyl farnesoate (MF) at the final step of the biosynthetic pathway. As the sesquiterpenoid precursor of the insect juvenile hormone III (JH III), MF has been suggested to play a vital role in regulating crustacean growth and reproduction. In this study, we report the identification of three isoforms of FAMeT transcript from the mud crab, Scylla paramamosain, which encode a peptide of 275, 278 and 280 amino acid residues respectively. Gene expression profiling by reverse transcriptase-polymerase chain reaction (RT-PCR) demonstrated that FAMeT has wide tissue distribution in S. paramamosain. In female S. paramamosain, the expression levels of FAMeT are significantly up-regulated in thoracic ganglion and down-regulated in eyestalk during ovarian development. In contrast, FAMeT expression levels increased in both thoracic ganglion and eyestalk during testicular development stages. During the molting stages of the mud crab, the mRNA abundance of FAMeT increased significantly in the eyestalk of females but not of males. FAMeT expression is therefore differentially regulated in male and female mud crab, during reproductive and molting stages. These results suggest that FAMeT is involved in many important functions, especially in the regulation of the growth, reproduction and molting processes, in S. paramamosain.