MULTIPLE SPECIES OF DEFECTIVE RNAS IN PLANTS INFECTED WITH CITRUS TRISTEZA VIRUS

Alemow (Citrus macrophylla) and sweet orange (C. sinensis) plants infe cted, respectively, with several Israeli and Florida isolates of the c itrus tristeza virus (CTV) were found to contain multiple species of R NA molecules with features similar to defective-interfering RNAs. Nort hern blot hybridizations of dsRNAs extracted from serial passages of t he Israeli VT isolate (CTV-VT) and from different plants infected with a single source of inoculum showed considerable variation both in the presence and in the relative abundance of the defective RNA (D-RNA) b ands. The D-RNA molecules were found to be encapsidated in the CTV par ticles. Sequence analysis of two VT D-RNA molecules of 2.7 and 4.5 kb revealed that they were composed of two regions corresponding to 1818 and 4036 nucleotides from the 5' and 938 and 442 nucleotides from the 3' termini of the CTV-VT genomic RNA, respectively. A short (ca. 0.8 k b) nonencapsidated single-stranded positive-sense RNA species was also found in infected plants. This ssRNA, which copurified with dsRNAs, w as shown by hybridization to encompass the 5'-terminal part of the CTV genome and might have an extensive secondary structure. (C) 1995 acad emic Press, Inc.