A short-chain dehydrogenase/reductase (SDR) detection for the Isoflavone reductase gene in Bulbophyllum and other orchids

Abstract

Bulbophyllum, the largest genus in Orchidaceae, is known for being rich in phenolic compounds. In this study, the polyphenol and antioxidant content of four Bulbophyllum species was compared to that of a Dendrobium sp. control. The transcript levels of eight genes involved in flavonoid biosynthesis and oxidative stress responses were then determined to identify correlations with flavonoid and antioxidant content. A positive correlation between flavonoid content and transcription level of isoflavone reductase (IFR), belonging to the short-chain dehydrogenase/reductase (SDR) superfamily, was observed in leaf and pseudobulb tissue of the orchids. IFR showed an extraordinarily high level of gene expression (max. 118-fold) in the pseudobulb tissue of Bulbophyllum species compared with that in the same tissue in several species of Dendrobium. A pair of primers derived from two conserved regions within the sequences of related SDRs (IFR, eugenol synthase, and phenylcoumaran benzylic ether reductase) from Dendrobium spp., Paphiopedilum sp., Phaseolus sp., Phoenix sp., Striga sp., and Vanda sp. were used to attain a full-length IFR from four Bulbophyllum spp., three Dendrobium spp. and one Vanda sp. The phylogenetic relationships of those SDRs reported in the NCBI database showed distinctive clusters between the closely related SDRs of each genus in the Orchidaceae, and the distantly related clusters of the other plant SDRs. This work describes an easy method for the quick detection and isolation of IFRs in Bulbophyllum and other orchid species.