Symptom responses and replication observed during mixed infections of Y330A plus SPMV on proso millet. (A) Y330A+SPMV-infected plants with no obvious symptoms (left leaf) or mild mosaic symptoms (right leaf). A leaf from a PMV+SPMV infected plant is also shown. RNA isolated from plants was used for RNA blots to detect PMV genomic (g) and subgenomic (sg) RNAs and SPMV RNA. (B) RT-PCR clones were sequenced to check the stability of the Y330A mutation. The tyrosine (TAC) to alanine (GCC) mutation on the PMV cDNA was stable in Y330A-infected plants with mild or severe symptoms, as shown in panel A.