Mutants of the Agrobacterium tumefaciens virA gene exhibiting acetosyringone-independent expression of the vir regulon.
Mutants of the Agrobacterium tumefaciens virA gene exhibiting acetosyringone-independent expression of the vir regulon.
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根癌农杆菌 virA 基因的突变体表现出 vir 调节子的乙酰丁香酮独立表达。
DOI：
10.1094/mpmi-4-400
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发表时间：
1991
期刊：
影响因子：
--
通讯作者：
Nester,EW
中科院分区：
文献类型：
--
作者：
Ankenbauer,RG;Best,EA;Palanca,CA;Nester,EW
分离出了根癌农杆菌virA基因中羟胺诱导的突变，其不需要植物酚诱导化合物乙酰丁香酮用于vir调节子诱导。该分离是基于在不存在乙酰丁香酮的情况下通过突变体virA基因座激活virB：lacZ和维雷：cat融合体。对其中三种vir 4（Ais）（乙酰丁香酮非依赖性信号传导）突变体进行了表征。所有三种突变体在不存在乙酰丁香酮的情况下均以高水平表达virB：：lacZ融合。一种virA（Ais）突变体，virA 112，在不存在诱导单糖和酸性生长条件下表现出vir基因表达，这两者通常是vir基因诱导所需的。virA 112突变体的表型是由VirA自身磷酸化位点His-474附近的甘氨酸变为谷氨酸引起的。冠瘿瘤的形成是一个复杂的过程，需要农杆菌vir（毒力）调节子的产物将细菌DNA转移到植物细胞中（Binns和Zambryski 1988; Zambryski 1989）。vir调节子分别受virA和vir G基因产物VirA和VirG的转录控制（Stachel and Nester 1986; Stachel and Zambryski 1986）。VirA/VirG对（Leroux等，1987; Winans等，1986）是原核双组分调节系统家族的成员，其用于响应特定的环境刺激而转录激活受试操纵子（综述参见Albright等，1989; Bourret等，1989; Gross等，1989; Stock等，1989）。VirA/VirG调节系统激活vir调节子转录，以响应特定的植物酚类代谢物（例如乙酰丁香酮）（Stachel et al. 1985）、植物衍生的单糖和衍生物（Ankenbauer and Nester 1990; Cangelosi et al. 1990; Shimoda et al. 1990）和酸性条件（Stachel et al. 1986; Winans et al. 1988）。VirG蛋白是一种转录激活因子，而VirA蛋白在感受诱导性刺激中起着至关重要的作用。VirA是一种跨膜蛋白，具有短的N-末端周质结构域和大的C-末端胞质区（Melchers et al. 1989; Winans et al. 1989）。VirA蛋白自磷酸化，
Hydroxylamine-induced mutations in the virA gene of Agrobacterium tumefaciens that do not require the plant phenolicinducing compound acetosyringone for vir regulon induction were isolated. The isolation was based on the activation of both virB: lacZ and virE: cat fusions by mutant virA loci in the absence of acetosyringone. Three of these vir4 (Ais)(acetosyringoneindependent signaling) mutants were characterized. All three mutants expressed a virB:: lacZ fusion at high levels in the absence of acetosyringone. One virA (Ais) mutant, virA 112, exhibited vir gene expression in the absence of inducing monosaccharides and acidic growth conditions, both of which are normally required for vir gene induction. The phenotype of the virA 112 mutant resulted from a glycine to glutamic acid change near His-474, the site of VirA autophosphorylation.The gram-negative phytopathogen Agrobacterium tumefaciens (Smith and Townsend) Conn is the etiologic agent of crown gall, a neoplastic disease of plants. Crown gall tumor formation is a complex process that requires the products of the Agrobacterium vir (virulence) regulon for transfer of bacterial DNA into plant cells (Binns and Thomashow 1988; Zambryski 1989). The vir regulon is under transcriptional control of the virA and vir G gene products, VirA and VirG, respectively (Stachel and Nester 1986; Stachel and Zambryski 1986). The VirA/VirG pair (Leroux et al. 1987; Winans et al. 1986) are members of a family of prokaryotic two-component regulatory systems that serve to transcriptionally activate subject operons in response to specific environmental stimuli (for reviews see Albright et al. 1989; Bourret et al. 1989; Gross et al. 1989; Stock et al. 1989). The VirA/VirG regulatory system activates vir regulon transcription in response to specific plant phenolic metabolites (eg, acetosyringone)(Stachel et al. 1985), plant-derived monosaccharides and derivatives (Ankenbauer and Nester 1990; Cangelosi et al. 1990; Shimoda et al. 1990), and acidic conditions (Stachel et al. 1986; Winans et al. 1988). Whereas the VirG protein serves as a transcriptional activator, the VirA protein has the crucial role in sensing the inducing stimuli. VirA is a transmembrane protein with a short N-terminal periplasmic domain and a large C-terminal cytoplasmic region (Melchers et al. 1989; Winans et al. 1989). The VirA protein autophosphorylates at