Epigenetic priming of terpenoid biosynthesis drives cultivar-specific efficient agarwood formation in Aquilaria sinensis

High-yielding cultivars of Aquilaria sinensis have been widely planted in Southern China over the last decade as a resource for the industrial production of agarwood. However, the molecular mechanisms underlying its superior yield remain unclear. Here, we used traditional planted 'Baimu' (BM) as rootstock and high-yielding 'Shuxinyou' (SXY) cultivar as scion to generate grafted plants. In 6-month-grafted plants, the SXY branch accumulated substantially more resin than that in the BM branch (alcohol-soluble extract) after 1 month of injury. We further performed integrated ATAC-seq (Assay for Transposase-Accessible Chromatin) and RNA-seq analyses to characterize chromatin accessibility and transcriptional responses under standardized injury conditions. Results indicated that the SXY branch had substantially more open chromatin overall (71,680 vs 51,489 ATAC peaks), with pronounced promoter accessibility. These cultivar-specific accessibility differences were associated with transcriptional activation of terpenoid biosynthesis after injury, including an accessibility difference at the AsTPS1 promoter that was accompanied by higher expression in SXY. Motif enrichment and network inference further nominated a candidate bHLH/bZIP module, with BHLH137 and HYH as candidate regulators at major nodes of the terpenoid pathway. These results are consistent with a candidate epigenetic-priming model in which pre-existing chromatin states may shape cultivar-specific metabolic potential; BHLH137 and HYH remain priorities for functional validation.