SATELLITE TOBACCO MOSAIC-VIRUS SEQUENCE VARIANTS WITH ONLY 5 NUCLEOTIDE DIFFERENCES CAN INTERFERE WITH EACH OTHER IN A CROSS PROTECTION-LIKE PHENOMENON IN PLANTS

The type strain of satellite tobacco mosaic virus (STMV) contains two major variants, designated type 5 (T5) and type 6 (T6), which can be e asily distinguished by RNase protection analyses. Clones containing cD NA of representative T5 and T6 STMV genomes have only five single-base differences in the entire 1059-nucleotide genome, and RNA transcribed from each clone is highly infectious when inoculated onto tobacco pla nts. The different RNase protection assay patterns can be used as gene tic markers to identify individual STMV variants and to follow the int eractions of variants and their progeny during coinfections in plants. The study described here investigated the effects of coinoculation an d various delayed inoculations of T5 and T6 variants on the compositio n of the progeny STMV populations in systemically infected tobacco tis sues. When T5 and T6 STMV RNAs were coinoculated or inoculated with 1- hr delays, the progeny from individual plants most often contained a m ixture of T5 and T6 genomes. However, when there was a 24-hr delay bet ween inoculations, the balance of T5 and T6 components in the progeny populations shifted toward predominance of the first variant inoculate d. With delays of 3 or 7 days only the first variant was evident in th e progeny populations, indicating that established replication of one STMV variant interferes with replication of another in a manner simila r to the cross protection phenomenon. (C) 1994 Academic Press, Inc.