The key role of phloroglucinol O-methyltransferase in the biosynthesis of Rosa chinensis volatile 1,3,5-trimethoxybenzene.

1,3,5-Trimethoxybenzene is a key component of the Chinese rose odor. This compound is synthesized in three successive methylation steps from phloroglucinol, the initial precursor. A novel, to our knowledge, phloroglucinol O-methyltransferase (POMT) characterized here methylates the first step to produce the intermediate 3,5-dihydroxyanisole, while two previously described orcinol O-methyltransferases catalyze the subsequent steps. We isolated POMT from rose petals and determined partial amino acid sequences of the purified enzyme. The full-length POMT cDNA was isolated and expressed in Escherichia coli. Both the native and recombinant POMT exhibited substrate specificity for phloroglucinol. POMT was expressed specifically in floral organs, in accordance with its role as a key enzyme in the synthesis of rose floral scent compounds.