Transient overexpression of β-glucosidase in leaves of Centaurium erythraea Rafn reduces the content of secoiridoid glucosides

Abstract

Centaurium erythraea Rafn, also known as common centaury, is a rich source of pharmacologically active specialized metabolites among which secoiridoid glucosides (SG) predominate. These compounds belong to the group of monoterpenoids, which are derived from the iridoid cyclopentan-C-pyran skeleton with β-D glucose linked at C1 position. Major SGs of C. erythraea (sweroside, swertiamarin, and gentiopicrin) are biosynthesized through general iridoid pathway via secologanin, and it has been recently proved that their catabolism starts with the deglycosylation step catalyzed by beta-glucosidases (BGlu). Two BGlu genes from C. erythraea (CeBGlu1 and CeBGlu2), with previously confirmed function, were transiently overexpressed in leaves of five month-old diploid and tetraploid centaury plants. Agroinfiltration of Agrobacterium tumefaciens GV3101 strain harboring genes of interest in TMV-based overexpression pJL-TRBO vector (pJL-TR-BO:CeBGlu1; pJL-TRBO:CeBGlu2) resulted in transient in planta overexpression of CeBGlu1 and Ce-BGlu2. Metabolic profiling of secoiridoids in leaves of diploid and tetraploid C. erythraea genotypes revealed that amounts of sweroside, swertiamarin, and gentiopicrin, were significantly reduced in agroinfiltrated leaves, especially when CeBGlu1 and CeBGlu2 were co-expressed with transgene silencing suppressor p19. Diploid plants displayed more pronounced decrease in SGs content than tetraploids. The effectiveness of gene overexpression was obviously altered by plant ploidy, and was under the control of post-transcriptional gene silencing mechanisms in the infiltrated tissues. Transgenes are more prone to transcriptional inactivation in C. erythraea tetraploids than in diploids. In conclusion, SGs-specific β-glucosidases could serve as a molecular target of biotechnological interest, in order to shape SG profiles of centaury and related economically important species of the Gentianaceae family.