Molecular diversity of tuliposide B-converting enzyme in tulip (): identification of the third isozyme with a distinct expression profile.

6-Tuliposide B (PosB), a major secondary metabolite that accumulates in tulip (), is converted to the antibacterial lactone, tulipalin B (PaB), by PosB-converting enzyme (TCEB). and , which encode TCEB, are specifically expressed in tulip pollen and roots, respectively, but are hardly expressed in other tissues (e.g. leaves) despite the presence of substantial PosB-converting activity, suggesting the existence of another TCEB isozyme. Here, we describe the identification of ("L" for leaf), a paralog of and , from leaves via native enzyme purification. The enzymatic characters of TgTCEB-L, including catalytic activity and subcellular localization, were substantially the same as those of TgTCEB1 and TgTCEB-R. However, did not exhibit tissue-specific expression. Identification of explains the PosB-converting activity detected in tissues where and transcripts could not be detected, indicating that tulip subtilizes the three TgTCEB isozymes depending on the tissue.