Detection of killer-independent dsRNA plasmids in Ustilago maydis by a simple and rapid method of extraction of dsRNA.

A novel method for efficient and rapid isolation of dsRNA molecules was developed. The dsRNA content of Ustilago maydis was reexamined; two distinct dsRNA classes were identified. Class I includes the dsRNA segments reported earlier for U. maydis virus systems and class II includes unencapsidated dsRNA molecules that were barely detected by the conventional extraction methods despite their high titer. Segments of the class II, some of which are reported for the first time, were further characterized; all the segments are independent of the killer system and other encapsidated dsRNA molecules. These segments are cytoplasmically transmitted and, in sharp contrast with class I-encapsidated dsRNA segments, their relative copy number decreases rapidly while entering the stationary phase.