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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.

Infectious clone vectors used widely in genetic research. While constructing soybean mosaic virus (SMV) clone vectors, we found that transformed Agrobacterium grew significantly different depending on the viral strains used. In particular, the clone vectors constructed with SMV SC15 significantly suppressed the growth of Agrobacterium . Recombinant and truncated virus vector experiments showed that the polymorphism of a P1 protein coding sequence of SC15 leads to the growth inhibition of Agrobacterium . But the lack of other protein encoding sequences, except for the sequence encoding coat protein, should reduce the ability of SC15 to suppress Agrobacterium growth. A vector (pCB301- att L-SC15P) compatible with the Gateway cloning system was constructed using this Agrobacterium inhibitory sequence. The results from the LR recombination reaction with pCB301- att L-SC15P and Agrobacterium transformation showed the valuable application potential of the Agrobacterium inhibitory sequence to serve as a negative screening factor for effective recombinant clone screening in Agrobacterium . Electronic supplementary material The online version of this article (10.1186/s13568-019-0840-3) contains supplementary material, which is available to authorized users.

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