Foliar application of methyl jasmonate does not increase terpenoid accumulation, but weakly elicits terpenoid pathway genes in sandalwood (<i>Santalum album</i> L.) seedlings

Abstract

The sesquiterpenoid rich essential oils of sandalwood (Santalum album L.) stems and roots are a highly sought commodity in the fragrance industry. Plantations of sandalwood are being established in northern Australia, however the valuable heartwood essential oils do not accumulate in substantial amounts before 10 years, while commercially viable harvests do not normally take place for at least 15 years. Inducing essential oil accumulation at an earlier stage, or increasing oil yield in mature trees, may have the potential to enhance the oil productivity of plantations. In this study, we investigated the effects of foliar application of methyl jasmonate on less than one-year-old sandalwood seedlings. Essential oil accumulation was unaffected in both stems and roots. However, at the gene transcript level, several key genes early in the biosynthesis of sandalwood oil components were induced in both leaves and stems. These results suggest that terpenoid biosynthesis in S. album does indeed respond to foliar application of methyl jasmonate, however the effects are small and the full biosynthesis of santalols is likely to be developmentally regulated.

Identification and functional characterization of three new terpene synthase genes involved in chemical defense and abiotic stresses in Santalum album

“…To date, little is known about the roles of α-terpineol produced by TPSs in plant defense. In S. album , the expression levels of genes coding for HMCR and FPPS were slightly induced in the leaves and stems of seedlings after the foliar application of 0.1% MeJA [46]. In our study, increased enzyme activities in the ROS antioxidant defense system and the sharp accumulation of SaTPS1 and SaTPS2 transcripts by exogenously applied MeJA and SA in leaves suggest that SaTPS1 and SaTPS2 play defensive roles against biotic stresses.…”

“…Another five TPSs, namely SamonoTPS1, SasesquiTPS1, Sasesquisabinene synthases (SaSQS1 and SaSQS2), and Sabisabolene synthase (SaBS), have also been identified [42, 45]. Kulheim et al (2014) attempted to enhance the essential oil productivity of sandalwood by applying 0.01% MeJA to the leaves of seedling younger than one year [46]. Their findings indicate that the expression levels of only two genes coding for hydroxymethylglutaryl CoA reductase (HMCR) and farnesyl diphosphate synthase (FPPS) were slightly induced in leaves and stems of seedlings in response to MeJA treatment.…”

Physiological and transcriptomic analyses reveal a response mechanism to cold stress in Santalum album L. leaves

“…However, the molecular regulation of santalol biosynthesis in sandalwood is largely unknown. A foliar application of methyl jasmonate caused a higher expression level of HMGR and the farnesyl diphosphate synthase gene in leaves and stems of treated S. album seedlings compared to untreated plants at 4 h, but expression of cytochrome P450 showed no change in both leaves and stems 29 . In the present study, several homologs of HMGR were dramatically up-regulated in leaves by cold stress, implying that this key rate-limiting enzyme in MVA is likely to play an important role in the response of S. album to external stress.…”

“…Külheim et al . discovered that several key genes in the terpenoid pathway were induced by spraying a 0.1% methyl jasmonate solution over the foliage, but valuable heartwood essential oils were not be detected in the leaves and stems of seedlings following this treatment 29 . Whether environmental stresses, including cold stress, affect the expression of terpene synthase genes and the accumulation of essential oil in sandalwood is unclear.…”