Molecular diversity of tuliposide B-converting enzyme in tulip (Tulipa gesneriana): identification of the root-specific isozyme

Abstract

6-Tuliposide B (PosB) is a glucose ester accumulated in tulip (Tulipa gesneriana) as a major secondary metabolite. PosB serves as the precursor of the antimicrobial lactone tulipalin B (PaB), which is formed by PosB-converting enzyme (TCEB). The gene TgTCEB1, encoding a TCEB, is transcribed in tulip pollen but scarcely transcribed in other tissues (e.g. roots) even though those tissues show high TCEB activity. This led to the prediction of the presence of a TCEB isozyme with distinct tissue specificity. Herein, we describe the identification of the TgTCEB-R gene from roots via native enzyme purification; this gene is a paralog of TgTCEB1. Recombinant enzyme characterization verified that TgTCEB-R encodes a TCEB. Moreover, TgTCEB-R was localized in tulip plastids, as found for pollen TgTCEB1. TgTCEB-R is transcribed almost exclusively in roots, indicating a tissue preference for the transcription of TCEB isozyme genes.

Identification of tuliposide G, a novel glucoside ester-type tuliposide, and its distribution in tulip

“…Biologically inert 6-PosA and 6-PosB are the storage forms (precursors) of antimicrobial α-methylene-γ-butyrolactones, tulipalin A (PaA) and tulipalin B (PaB), respectively, which are formed from the C-6 acyl group (Figure 1). The conversion reactions of 6-PosA to PaA and 6-PosB to PaB in planta are catalyzed by PosA-converting enzyme [tuliposide A-converting enzyme (TCEA)] and PosB-converting enzyme (TCEB), respectively, which are unique non-ester-hydrolyzing carboxylesterases we discovered previously [3,[6][7][8][9][10][11][12][13].…”