Integrated electronic tongue, metabolomic and transcriptomic analyses link tyramine-conjugated phenylpropanoid amides to spatial bitterness in Pleioblastus maculatus bamboo shoots

Abstract

Bamboo shoots are widely consumed vegetables in East and Southeast Asia, but the metabolites responsible for spatial bitterness variation within a single shoot and the underlying transcriptional mechanisms have not been identified. We combined electronic tongue phenotyping with metabolomics (885 metabolites) and transcriptomics (33,709 transcripts) across the tip, middle and basal sections of Pleioblastus maculatus shoots. Light exclusion and soil-mulching treatments were applied to separate photic from non-photic environmental signals. Bitterness peaked in the middle section. Two tyramine-conjugated hydroxycinnamic acid amides, N-feruloyltyramine and N-coumaroyltyramine, accumulated preferentially in the middle section and correlated with the measured bitterness pattern. Expanded phenylpropanoid gene families showed paralog-level expression divergence along the shoot axis. Two BAHD acyltransferases, PmAT15 and PmAT15-like, were preferentially expressed in the middle section, whereas paralogs directing monolignol biosynthesis predominated in the base. Total phenolic content correlated most strongly with bitterness among all physiological indicators measured. Soil mulching reduced middle-section bitterness by 69.7%, whereas light exclusion alone had no significant effect. These results showed that paralog-level expression divergence within phenylpropanoid gene families was associated with the spatial distribution of bitter metabolites in bamboo shoots. Non-photic signals associated with soil burial, rather than light deprivation, were the primary environmental cues regulating this distribution.