Specific sequence changes in the 5'-terminal region of the genome of satellite tobacco mosaic virus are required for adaptation to tobacco mosaic virus.

Abstract

The genome of satellite tobacco mosaic virus (STMV) adapted to tobacco mosaic virus (TMV), tomato mosaic virus or green tomato atypical mosaic virus consistently had two single base deletions at positions 1 and 61, corresponding to bases A and G, respectively, as compared to the type-strain genome which is naturally adapted to tobacco mild green mosaic virus (TMGMV). Transcript RNAs (STMV(TMV)) from clone pSTMV(TMV) which captured the deletions at positions 1 and 61 were infectious when co-inoculated to tobacco plants with either TMV or TMGMV at infection frequencies of > 90%. Two new STMV variants were created to investigate whether both deletions were essential for adaptation to TMV. These were STMV(TMGMV) deltaA1, which had the A at position 1 (A1) deleted, and STMV(TMGMV) deltaG61, which lacked G61. STMV(TMGMV) deltaA1 was infectious (75% frequency) in the presence of either TMV or TMGMV. Virion RNA of STMV(TMGMV) deltaA1 lost G61 after one infection cycle with TMV. This deletion did not occur in co-infections with TMGMV. STMV(TMGMV) deltaG61, like the clone STMV(TMGMV), was infectious (100% frequency) with TMGMV but TMV did not support this clone. When Nicotiana benthamiana protoplasts were transfected with STMV(TMGMV), STMV(TMGMV) deltaA1 or STMV(TMV), STMV replicated when TMGMV was the helper virus. STMV(TMV) and STMV(TMGMV) deltaA1 replicated in the presence of helper TMV, but STMV(TMGMV) did not, the same result as in whole plants. The deletion of A1 is thus essential for initial STMV adaptation to TMV and the eventual deletion of G61 is a predicted additional change.

Satellite RNAs and Satellite Viruses of Plants

“…Among them, only Satellite tobacco mosaic virus (STMV) has a rod-shaped virus as the helper [31]. Of note, deletion of nucleotides A and G at positions 1 and 61, respectively, of STMV, which is naturally adapted to Tobacco mild green mosaic virus , is required for adaptation to other helper viruses, namely Tobacco mosaic virus (TMV), Tomato mosaic virus or Green tomato atypical mosaic virus [32]. Satellite viruses can co-evolve with the helper viruses whenever they encounter each other.…”

In Vitro- and In Vivo-Generated Defective RNAs of Satellite Panicum Mosaic Virus Define cis -Acting RNA Elements Required for Replication and Movement

“…In the adaptation of STMV to the nonoriginal helper viruses, tomato mosaic virus and green tomato atypical mosaic virus, nucleotides A and G at positions 1 and 61 in the 5Ј UTR were consistently deleted (12), suggesting that the 5Ј UTR plays a role in the helper virus-specific replication of STMV. However, SPMV accumulation in plants and protoplasts was reduced only slightly by the deletion of nt 17 to 67 within the 5Ј UTR (Fig.…”

“…2 and 3). UTRs (1,12,16,17). For example, the cis-acting elements necessary for the replication of STNV are embedded in three hairpin-like structures on the 5Ј UTR and in two discrete regions identified as the 3Ј-proximal terminal sequence and the sequence immediately adjacent to the CP ORF in the 3Ј UTR (1).…”