A tobacco ringspot virus-based vector system for gene and microRNA function studies in cucurbits

Cucurbits are economically important crops worldwide. The genomic data of many cucurbits are now available. However, functional analyses of cucurbit genes and noncoding RNAs have been impeded because genetic transformation is difficult for many cucurbitaceous plants. Here, we developed a set of tobacco ringspot virus (TRSV)-based vectors for gene and microRNA (miRNA) function studies in cucurbits. A TRSV-based expression vector could simultaneously express GREEN FLUORESCENT PROTEIN (GFP) and heterologous viral suppressors of RNA silencing in TRSV-infected plants, while a TRSV-based gene silencing vector could knock down endogenous genes exemplified by PHYTOENE DESATURASE (PDS) in Cucumis melo, Citrullus lanatus, Cucumis sativus, and Nicotiana benthamiana plants. We also developed a TRSV-based miRNA silencing vector to dissect the functions of endogenous miRNAs. Four representative miRNAs, namely, miR159, miR166, miR172, and miR319, from different cucurbits were inserted into the TRSV vector using a short tandem target mimic strategy and induced characteristic phenotypes in TRSV-miRNA-infected plants. This TRSV-based vector system will facilitate functional genomic studies in cucurbits.     

人突触小体相关蛋白25单克隆抗体的制备及初步鉴定

目的:制备抗人突触小体相关蛋白25(SNAP25)的鼠源单克隆抗体。方法:利用大肠杆菌表达SNAP25蛋白,纯化后免疫BALB/c小鼠制备杂交瘤细胞,筛选针对SNAP25的阳性杂交瘤细胞株,鉴定抗体亚型;用杂交瘤细胞株制备腹水单抗,纯化后利用SDS-PAGE检测抗体纯度。结果:表达并纯化得到纯度大于90%的SNAP25蛋白,免疫小鼠后经2轮筛选得到12株阳性杂交瘤细胞株,其中抗体重链包括IgG1、IgG2型,轻链大部分为κ链;选择具有相对较高抗原结合活性的14号杂交瘤细胞株制备腹水,纯化后得到纯度大于90%的抗体。结论:获得1株高纯度的针对SNAP25的鼠源单克隆抗体,为肉毒毒素的检测奠定了基础。     

The conserved aromatic residue W122 is a determinant of potyviral coat protein stability,replication, and cell-to-cell movement in plants

Coat proteins (CPs) play critical roles in potyvirus cell-to-cell movement. However, the underlying mechanism controlling them remains unclear. Here, we show that substitutions of alanine, glutamic acid, or lysine for the conserved residue tryptophan at position 122 (W¹²²) in tobacco vein banding mosaic virus (TVBMV) CP abolished virus cell-to-cell movement in Nicotiana benthamiana plants. In agroinfiltrated N. benthamiana leaf patches, both the CP and RNA accumulation levels of three W¹²² mutant viruses were significantly reduced compared with those of wild-type TVBMV, and CP accumulated to a low level similar to that of a replication-deficient mutant. The results of polyprotein transient expression experiments indicated that CP instability was responsible for the significantly low CP accumulation levels of the three W¹²² mutant viruses. The substitution of W¹²² did not affect CP plasmodesmata localization or virus particle formation; however, the substitution significantly reduced the number of virus particles. The wild-type TVBMV CP could complement the reduced replication and abolished cell-to-cell movement of the mutant viruses. When the codon for W¹²² was mutated to that for a different aromatic residue, phenylalanine or tyrosine, the resultant mutant viruses moved systemically and accumulated up to 80% of the wild-type TVBMV level. Similar results were obtained for the corresponding amino acids of W¹²² in the watermelon mosaic virus and potato virus Y CPs. Therefore, we conclude that the aromatic ring in W¹²² in the core domain of the potyviral CP is critical for cell-to-cell movement through the effects on CP stability and viral replication.