Overexpression of the gibberellin 20-oxidase gene from Torenia fournieri resulted in modified trichome formation and terpenoid metabolities of Artemisia annua L.

Abstract

Gibberellins (GAs) are diterpenoid hormones, control various physiological developments in plants. The role of gibberellins on morphology and secondary metabolite production was examined in Artemisia annua, a medicinal plant that has been acknowledged as a source of artemisinin, an antimalarial compound. Subsequently, the GA20ox gene from Torenia fournieri (TfGA20ox2) was transferred to A. annua by Agrobacterium-mediated transformation. Compared with wild type plants, all nine transgenic plants showed significantly higher plant heights and artemisinin contents. The highest artemisinin content and yield in TfGA20ox2-overexpressing plants was around two-fold higher than wild type. Moreover, transgenic plants had higher numbers of branches (52.4%) and greater branch lengths (60–203%), but smaller leaf size (77.6%). Interestingly, relative to wild type the number and size of glandular trichomes in transgenic leaves was about 30 and 35% higher, respectively. From GC–MS analysis, the proportion of diterpenes in transgenic plant extracts was 1.5-fold lower than those noticed in wild type, while the proportion of sesquiterpenes was increased about 1.6 times when compared to wild type. However, the content proportion of monoterpenes showed a slightly increase, whereas the level of triterpenes showed no variation. In addition, two monoterpenes (eucalyptol and borneol), four sesquiterpenes (α-caryophyllene, β-guaiene, δ-cadinene and β-cubebene) and one triterpenes (isomultiflorenone) were detected only in transgenic extract, whereas d-α-tocopherol, a diterpenoid compound was found only in wild type but not transgenic plant. These results suggested that gibberellins play a significant role in regards to morphology, trichome formation and terpenoid metabolite production in A. annua.