Impact of drought stress on monoterpene biosynthesis in sage (Salvia officinalis)The : Dehydrins and monoterpene synthases as molecular markers

Abstract

The product quality of medicinal plants is determined by the quality and quantity of the particular natural products. Deliberate modifications require a comprehensive knowledge on the biosynthetic pathways and their regulations. In this context, the complex interactions between stress and secondary metabolism are of special interest. This study was aimed to elucidate exemplarily the impact of drought stress on the biosynthesis and accumulation of monoterpenes in sage. For this, the applicability of dehydrins as molecular stress markers as well as the gene expression of monoterpene synthases had been studied. Dehydrin gene SoDHN was isolated from sage leaves. The cDNA sequence exhibits a total length of 1000 bp with a putative open reading frame of 735 bp (accession number: AEB77936.1). SoDHN is constitutively expressed in leaves; however, its expression is significantly increased by drought stress. Western blot analysis revealed that the SoDHN protein also is already present in non-stressed leaves; nevertheless, the accumulation of dehydrin protein is significantly enhanced under drought stress. In contrast to the transient transcription, the abundance of the dehydrin protein remained stable throughout the entire period. Thus, for evaluating the stress status, in addition to the gene expression also the abundance of the protein has to be determined. Drought stress also impacts on the expression of monoterpene synthases; e.g. the amounts of mRNA for bornyl diphosphate synthase and cineole synthase already are strongly enhanced 2h after detaching the leaves and reach a maximum after 6h. Obviously, the monoterpene biosynthesis is – apart from the “passive” enhancement due to the drought-related over-reduced states – also “actively” increased by enhancing the biosynthetic capacity. This points out that monoterpenes – apart from their ecological functions – also are relevant to the dissipation of the massive over-supply of energy generated in leaves under drought stress.