E3-ubiquitin ligases are known to confer abiotic stress responses in plants. In the present study, GmPUB21, a novel U-box E3-ubiquitin ligase-encoding gene, was isolated from soybean and functionally characterized. The expression of GmPUB21, which possesses E3-ubiquitin ligase activity, was found to be significantly up-regulated by drought, salinity, and ABA treatments. The fusion protein GmPUB21-GFP was localized in the cytoplasm, nucleus, and plasma membrane. Transgenic lines of the Nicotiana benthamiana over-expressing GmPUB21 showed more sensitive to osmotic, salinity stress and ABA in seed germination and inhibited mannitol/NaCl-mediated stomatal closure. Moreover, higher reactive oxygen species accumulation was observed in GmPUB21 overexpressing plants after drought and salinity treatment than in wild-type (WT) plants. Contrarily, silencing of GmPUB21 in soybean plants significantly enhanced the tolerance to drought and salinity stresses. Collectively, our results revealed that GmPUB21 negatively regulates the drought and salinity tolerance by increasing the stomatal density and aperture via the ABA signaling pathway. These findings improved our understanding of the role of GmPUB21 under drought and salinity stresses in soybean.

Soybean is an important grain and oil crop worldwide; however, the yield and seed quality of which are seriously affected by Soybean mosaic virus (SMV). As efficient detection technology is crucial for the field management of SMV, novel immunological detection methods were developed in the present study. According to the phylogenetic analysis, the CP coding sequence of SMV-SC7 was selected for the prokaryotic expression of the recombinant SMV-CP. Purified SMV-CP was used for the development of polyclonal antibodies (PAb) against the SMV-CP (PAb-SMV-CP) and monoclonal antibodies (MAb) against SMV-CP (MAb-SMV-CP). Subsequently, the PAb-SMV-CP was used for the development of a novel DAS- quantitative ELISA (DAS-qELISA) kit, of which the sensitivity was greater than 1:4000, and this could be used for the quantitative detection of SMV in China. Meanwhile, the MAb-SMV-CP was labeled with colloidal gold, and then was used for the development of the SMV-specific gold immunochromatography strip (SMV-GICS). The SMV-GICS gives accurate detection results through observed control lines and test lines in 5 to 10 min, sharing the same sensitivity as RT-PCR, and can be used for rapid, accurate and high-throughput field SMV detection. The DAS-qELISA kit and the SMV-GICA strip developed in this study are SMV-specific, sensitive, cheap and easy to use. These products will be conducive to the timely, efficient SMV epidemiology and detection in major soybean-producing regions in China and abroad.

The Ferredoxin-NADP reductase (FNR) gene plays a significant role in NADPH production, carbon assimilation, antioxidation, and cross-talking between chloroplasts and mitochondria in plants. This study aims to know the functional response of the soybean FNR gene (GmFNR) during a soybean mosaic virus (SMV) infection. For this purpose, we developed the bean pod mottle virus (BPMV)-based gene construct (BPMV-GmFNR) and used it to silence the GmFNR gene in resistant and susceptible lines. The results showed that GmFNR expression decreased to 50% in the susceptible line, compared to 40% in the resistant line. The silencing of GmFNR reduces the photosynthetic capacity and CAT activity of both lines compared to their respective controls. In addition, the H₂O₂ content increased significantly in the susceptible line, whereas the resistant line did not exhibit any change. Further, an SMV infection in the silencing plants of the susceptible line resulted in serious morphological changes and increased the SMV NIa-protease transcript accumulation compared to its control plants. However, the same impact was not observed in the resistant line. The yeast two-hybrid system, BIFC assay, and quantitative real-time polymerase chain reaction (qRT-PCR) analyses revealed that the GmFNR was interacting with EF1A and coincided with the increased SMV accumulation. The results obtained in this study improve the understanding of the soybean FNR gene response during SMV infection and provide a novel insight into the SMV resistance mechanism.