SummaryViral infections cause plant chlorosis, stunting, necrosis or other symptoms. The down-regulation of chloroplast-related genes (ChRGs) is assumed to be responsible for chlorosis.We identified the differentially expressed genes (DEGs) in Rice stripe virus (RSV)-infected Nicotiana benthamiana, and examined the contribution of 75 down-regulated DEGs to RSV symptoms by silencing them one by one using Tobacco rattle virus (TRV)-induced gene silencing.Silencing of 11 of the 75 down-regulated DEGs caused plant chlorosis, and nine of the 11 were ChRGs. Silencing of a down-regulated DEG encoding the eukaryotic translation initiation factor 4A (eIF4A) caused leaf-twisting and stunting that were visible on RSV-infected N. benthamiana. A region of RSV RNA4 was complementary to part of eIF4A mRNA and virus-derived small interfering (vsiRNAs) from that region were present in infected N. benthamiana. When expressed as artificial microRNAs, those vsiRNAs could target NbeIF4A mRNA for regulation.We provide experimental evidence supporting the association of ChRGs with chlorosis and show that eIF4A is involved in RSV symptom development. This is also the first report demonstrating that siRNA derived directly from a plant virus can target a host gene for regulation.

Pepper mild mottle virus (PMMoV) was detected by RT-PCR in all 42 pepper sauce samples from the 10 main manufacturing provinces in China at concentrations ranging from 3.8 to 8.8 (Log10 copies/mL). Their coat protein nucleotide sequences had 97.4 to 100 % identity to each other and 92.4 to 100 % to other published isolates. The samples remained infectious to N. benthamiana, indicating that commercial trade in sauce could contribute to the natural spread of PMMoV.