Expression of host S-adenosylmethionine decarboxylase gene and polyamine composition in aphid bacteriocytes.

Differential cDNA display and quantitative RT-PCR revealed that mRNA of host S-adenosylmethionine decarboxylase (SAMDC) was abundant only in the aphid endosymbiotic system well organized in young hosts, suggesting that SAMDC plays some important roles in the system. SAMDC is a key enzyme to synthesize polyamines that are known to be involved in a large array of biological events including protein synthesis, DNA stabilization, DNA replication, and cell proliferation. As the first step to investigate roles of polyamines in the endosymbiotic system, polyamine composition in bacteriocytes was determined by high performance liquid chromatography. As a result, we found that bacteriocytes contained virtually an only single polyamine, spermidine. The spermidine content of bacteriocytes fluctuated with time in the course of development and aging of the host aphid. This is the first report of polyamine assessment in a prokaryote-eukaryote endocellular symbiotic system, which demonstrated a unique polyamine composition.