Characterization of four terpene synthase genes involved in nerolidol and linalool biosynthesis in Santalum album leaves induced by methyl jasmonate.

Santalum album is highly valued for its fragrant essential oil from heartwood. Volatile terpenoids involved in aroma formation in plants can be emitted in response to a variety of environmental stresses. However, the regulatory mechanisms underpinning the response of S. album to external stresses are not yet known. In this study, the regulatory mechanism of S. album leaves was investigated after the application of methyl jasmonate (MeJA), a stressor. Eight classes of volatile organic compounds were identified in S. album leaves, including terpenes, aldehydes, alcohols, ketones, esters, benzenoids, alkanes and heterocyclic compounds. In total, 15 terpenoids, such as ocimene, linalool, nerolidol and α-farnesene, were considerably induced 6 h after MeJA treatment, amounting to 38.01 % of all volatiles. Notably, transcript levels of the genes in the MVA pathway were enhanced by 2- to 8-fold after 6 h of MeJA treatment compared to the control. Exogenously applied MeJA resulted in the significant upregulation of ten terpene synthase (SaTPS) genes. In vitro enzyme activity assays confirmed that four SaTPS recombinant proteins converted substrates into (E)-nerolidol and linalool. Overexpression of the four SaTPS genes produced (E)-nerolidol, (Z)-nerolidol and linalool in sandalwood callus. These results suggest that the four SaTPS genes have the ability to synthesize nerolidol and linalool in S. album leaves in response to MeJA treatment. This study provides insight into the regulatory mechanism of the biosynthesis of terpenoids in S. album in response to an environmental stress.