The molecular mechanism underlying the resistance to soybean mosaic virus (SMV) infection in soybean is of great importance as soybean mosaic caused by SMV has become one of the major soybean disease worldwide. We have previously performed transcriptome analysis of SMV-inoculated soybean after inhibition of H₂O₂ production and have identified a differentially expressed C₂H₂-type single zinc finger protein gene, Glyma.18G003600.1, named GmSZFP. In this study, we use virus induced gene silencing (VIGS) technique to investigate the function of GmSZFP in soybean-SMV interaction, providing a foundation for further investigation of the molecular mechanism of GmSZFP in soybean-SMV interaction.

Soybean cultivar Jidou 7 and SMV strains SC-8 (susceptive) and N3 (resistance) were used as the materials in this study. Bioinformatic analysis was conducted to predict the protein domains of GmSZFP; its transcription factor activity was measured by transcriptional activation assay in yeast; the expression characteristics of GmSZFP at the transcriptional level in soybean-SMV interaction were verified by real-time quantitative PCR (qPCR); and the function of GmSZFP in soybean-SMV interaction was investigated by VIGS technique.

The CDS region of GmSZFP gene was cloned; amino acid sequence analysis and transcriptional activation assay in yeast revealed that GmSZFP is a C₂H₂-type zinc finger protein transcription factor with transcriptional activation activity; qPCR results showed that GmSZFP was strongly induced by SMV inoculation, and the expression pattern was different between the compatible and the incompatible combinations. The expression of GmSZFP was elevated after SMV inoculation, and then decreased in the incompatible combination, and the expression level of GmSZFP was significantly lower in the compatible combination than that in the former. Moreover, the expression level of GmSZFP was found to be reduced to the level that is similar to the level in the compatible combination that was pre-inoculated with imidazole, indicating that GmSZFP responds to SMV infestation at the transcriptional level and is regulated by H₂O₂; After silencing GmSZFP, we found that callose at the SMV inoculation site was greatly reduced compared to the control, and the expression of callose synthase genes GmGSL7c and GmGSL12b was reduced compared to the control, and the expression of callose hydrolase gene BG was elevated compared to the control; In addition, after GmSZFP was silenced, the virus spread outward to a distance of 2 mm at 72 h and to a distance of 3 mm at 96 h from the central source after SMV was inoculated in a small area, while the expression of SMV capsid protein (CP) gene was not detectable outside the inoculation site in control leaves; 10 d after SMV inoculation, the upper leaves (of the SMV inoculated leaves) in the GmSZFP-silenced plants showed mosaic, greening and curling symptoms, and CP gene was expressed, indicating that silencing of GmSZFP enabled SMV to transport in an unrestricted manner.

GmSZFP is a canonical C₂H₂-type mono-zinc finger protein, and the GmSZFP gene plays a positive regulatory role in soybean resistance to SMV infection.