Regulation of lignin biosynthesis in fruit pericarp hardening of mangosteen (Garcinia mangostana L.) after impact

Abstract

Pericarp hardening in fresh mangosteen (Garcinia mangostana L.) fruit is a rapid response to mishandling during and after harvest. Firmness, lignin content and lignin composition (G and S lignin) increased rapidly, while total free phenolic content decreased in damaged mangosteen pericarp following impact. Application of nitrogen to the fruit after impact reduced these effects, compared with fruit kept in ambient air. The majority of the genes encoding the mangosteen lignin biosynthetic pathway, and a full length MYB transcription factor (R2R3 MYB), were isolated. Expression analysis using qPCR showed that of the genes encoding enzymes in lignin biosynthesis, only GmCCoAMT and GmF5H increased after impact and correlated with increases in firmness and lignin content. The transcript level of a stress-related R2R3 MYB transcription factor was significantly increased by impact, and delayed by elevated nitrogen. These results suggest that pericarp hardening of mangosteen after impact is due to rapid transcriptional activation of late steps of the lignin biosynthetic pathway, potentially via up-regulation of transcription factors such as R2R3 MYBs.