Isolation of good quality RNA from plant tissues such as mangosteen is troublesome and challenging because they are rich in secondary metabolites such as phenolic compounds and polysaccharides that coprecipitate with nucleic acids. The phenolic substances interact irreversibly with nucleic acids and proteins1, leading to their oxidation and degradation2 and finally render RNA unsuitable for downstream purposes.
Previously, two RNA extraction protocols have been tried on mangosteen tissues i.e. the methods described by Rochester et al. 3 and Matsumura et al. 4, respectively; however, the RNA isolated were partially degraded, brown in color and difficult to dissolve (Figure 1 a-b, Table 1). This may due to the browning effect1, whereby a brown color supernatant is developed upon oxidation of the homogenate. The poor quality of RNA may attribute to coprecipitation of polysaccharides and oxidation of phenolic compounds that interact irreversibly with nucleic acids1,2.
In this study, a method was developed to isolate good quality RNA from leaves and flowers of mangosteen. In this method, polyvinylpyrrolidone (PVP) was added in the extraction buffer, so that it can bind to the phenolic compounds which are then eliminated by ethanol precipitation. The protocol described here is simple, fast and does not require ultracentrifugation.