SaMYC2 acts as a key transcriptional activator of terpenoid biosynthesis and is subject to feedback regulation by SaGNAT01 in Santalum album L.

Abstract

Santalum album L. (sandalwood) is an economically important tree species valued for its heartwood essential oil, which is primarily composed of terpenoids. However, the transcriptional regulatory mechanisms governing terpenoid biosynthesis in sandalwood remain poorly understood. Here, we identified a nuclear-localized MYC transcription factor, SaMYC2, that plays a critical role in regulating terpenoid biosynthesis. DNA affinity purification sequencing (DAP-seq) analysis revealed that a cluster of genes involved in mono- and sesquiterpenoid biosynthesis are direct targets of SaMYC2. Electrophoretic mobility shift assay (EMSA) and dual luciferase reporter (DLR) assay confirmed that SaMYC2 binds to the promoters of two key sesquiterpenoid biosynthesis genes, SaSSy and SaCYP736A167 , and activates their expression. We further demonstrated that SaGNAT01 , which encodes a ubiquitin-like protein, is transcriptionally activated by SaMYC2. Intriguingly, SaGNAT01 interacts with SaMYC2 both in vitro and in vivo . This interaction attenuates the transcriptional activation activity of SaMYC2 to the SaSSy and SaCYP736A167 promoters without affecting SaMYC2 protein stability. Moreover, heterologous overexpression of SaMYC2 in tomato altered its fruit volatile profile and increased the levels of several terpenoids that also occur in sandalwood oil. Collectively, our findings establish SaMYC2 as a key transcriptional activator for improving sandalwood oil yield and uncover a previously unknown self-regulatory feedback mechanism wherein SaMYC2-activated SaGNAT01 modestly attenuates terpenoid biosynthesis.