Sequence variability in plant viroid RNAs

Abstract

Viroids are the smallest known pathogens in nature, and to date have been found only in flowering plants. Only 12 have been described so far (Table 1), and they consist of singlestranded, circular RNA molecules which vary in length from 246 to 375 nucleotides and are not encapsidated. The names that have been given to them are generally descriptive of the symptoms they cause. In the field, they continue to cause diseases of varying severity and economic importance. A historical perspective is given in the book by Diener 17 while several recent reviews18-22 provide a detailed coverage of the determination of the sequence, secondary structure, and properties of viroids. This chapter presents t..