NEW SATELLITE RNAS, BUT NO DI RNAS, ARE FOUND IN NATURAL-POPULATIONS OF TOMATO BUSHY STUNT TOMBUSVIRUS

A collection of 57 field isolates of the tombusvirus tomato bushy stun t virus was obtained from eggplant and tomato during 1994-1997 and was examined for the presence of defective interfering (DI) RNA species b y Northern blot hybridization and RT-PCR. No DI RNA species were detec ted associated with any of the field TBSV isolates. However, serial pa ssaging of two field isolates in Nicotiana clevelandii at high multipl icity of infection resulted in the rapid generation of DI-like RNA spe cies, indicating that the absence of DI RNAs in natural populations of the virus was not due to the inability of the TBSV field isolates to generate them in a suitable host. The results indicate that DI RNAs ma y not play a role in modulating natural TBSV infections in the hosts e xamined. In 4 of 57 isolates analysed we have detected less than full- length RNAs and we show here that they are true satellite RNAs. Two di fferent satellite RNA species were detected, named TBSV sat RNAs B1 (8 22 nt) and B10 (612 nt). TBSV sat RNAs lack significant open reading f rames and do not present sequence homology except in a central box tha t is also conserved in TBSV-Ch genomic RNA and in all the DI RNAs deri ved from it TBSV sat RNA B10 attenuated the symptoms induced by the he lper virus in N. clevelandii while sat RNA B1 did not modify the sympt oms. This is the first report of sat RNAs associated with TBSV and the first time that sat RNAs are associated with natural tombusvirus infe ctions. (C) 1997 Academic Press.