Simple and efficient method for functional RNA extraction from tropical medicinal plants rich in secondary metabolites

Abstract

Isolation of high-quality functional RNA is prerequisite to facilitate any study related to gene expression and also for downstream applications such as reverse transcription-polymerase chain reaction (RT-PCR), suppression subtractive hybridization (SSH) library construction, differential display (DD), real-time PCR and northern hybridization of medicinal plants. Tropical medicinal plants are rich in polysaccharides, polyphenolics and secondary metabolites that are reported to interfere with the successful RNA isolation. Conventional approaches for the extraction of functional RNA are often time-consuming and need expensive reagents. Moreover, these methods can yield only poor quality and quantity of functional RNA. In our laboratory, we have aimed at establishing a simple and efficient functional RNA extraction procedure. For this, a sodium dodecyl sulfate (SDS) based protocol free of guanidine isothiocyanate was adopted. The total extracted RNA remains in the upper aqueous phase, at acidic conditions leaving DNA and proteins in the lower organic phase. This principle is used in this protocol and the modifications made in the SDS-acid phenol RNA extraction protocol were found to be helpful for extracting RNA from tissues containing large quantities of secondary metabolites. This method can be completed within 3 hours with purity ranges from 1.8-2.0 as confirmed by A 260/280 spectrophotometric readings. The above-described RNA extraction protocol works well with all the tissues examined so far, where standard RNA isolation methods failed. INTRODUCTIONTropical medicinal plants have been largely exploited for therapeutic purposes by present-day researchers. Effective conservation and sustainable utilization of plant biodiversity is indispensable for meeting the present and future requirements of medicinal plants. These medicinal plants are rich sources of alkaloids, polyphenols, polysaccharides, secondary metabolites, terpenoids and these phyto compounds have dragged the attention of contemporary researchers. Production of valuable therapeutic compounds from medicinal plants could be made possible through metabolic engineering and recombinant DNA technology (Titanji et al. 2007). The application of modern molecular biology techniques may help in better understanding and conservation of medicinal plants. These tools can unravel the various bioactive compounds with therapeutic significance at the molecular level. Good quality functional RNA extraction is the most important step in gene expression analysis studies (Ghangal et al. 2009). However, RNA extraction from tissues having higher polyphenols, polysaccharides and secondary metabolite contents became a difficult task. The phenolic compounds readily get oxidised to form quinones. These quinones can bind easily with nucleic acids and act as a barrier for good quality RNA isolation (Wang et al. 2008).Several RNA isolation protocols for medicinal plants has been developed or modified and certain commercial kits were also introduced (John 1992, MacKenzie e...

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