Mur L A, Bi Y M, Darby R M, Firek S, Draper J
Botany Department, University of Leicester, UK.
Plant J. 1997 Nov;12(5):1113-26. doi: 10.1046/j.1365-313x.1997.12051113.x.
To investigate the role of salicylic acid (SA) in the hypersensitive response (HR) its accumulation was compromised during different phases of lesion development by differential expression of a salicylate hydroxylase gene (SH-L). Constitutive suppression of SA accumulation was achieved by expression of a gene fusion between the CaMV35S promoter (35S) and SH-L. Using the H2O2-responsive AoPR1 promoter to drive SH-L SA accumulation could be compromised at an early stage, on lesion formation and possibly prior to visible necrosis, whilst use of the salicylate-responsive PR1a promoter reduced SA accumulation at a later stage as lesions expand. TMV infection of 35S-SH-L and AoPR1-SH-L, but not PR1a-SH-L, tobacco resulted in significantly greater rates of lesion growth than in wild-type tobacco. TMV was detected in asymptomatic tissue surrounding lesions only in 35S-SH-L and AoPR1-SH-L lines; subsequently these transgenic lines exhibited a 'spreading-necrosis' originating from the lesion which entered the stem and eventually other leaves, a phenotype which could be correlated with the presence of TMV particles. Analysis of TMV-infected and 'temperature-shifted' tobacco indicated that both 35S-SH-L and AoPR1-SH-L, but not PR1a-SH-L, transgenics exhibited delayed cell-death compared to wild-type infections. We propose that the SH-L phenotypes indicate that early SA accumulation is a major factor in preventing viral escape, via mechanism(s) which may include influencing the rate of host-cell death and, possibly, an effect on viral function.
为了研究水杨酸（SA）在过敏反应（HR）中的作用，通过水杨酸羟化酶基因（SH-L）的差异表达，在病斑发育的不同阶段破坏其积累。通过表达CaMV35S启动子（35S）和SH-L之间的基因融合来实现SA积累的组成型抑制。利用H2O2响应性的AoPR1启动子驱动SH-L，SA积累在早期、病斑形成时以及可能在可见坏死之前就会受到破坏，而使用水杨酸响应性的PR1a启动子在病斑扩展的后期会降低SA积累。用烟草花叶病毒（TMV）感染35S-SH-L和AoPR1-SH-L烟草，但不感染PR1a-SH-L烟草，导致病斑生长速率比野生型烟草显著更高。仅在35S-SH-L和AoPR1-SH-L系的病斑周围无症状组织中检测到TMV；随后，这些转基因系表现出从病斑开始的“扩散性坏死”，坏死进入茎部并最终蔓延到其他叶片，这种表型与TMV颗粒的存在相关。对感染TMV和“温度转换”烟草的分析表明，与野生型感染相比，35S-SH-L和AoPR1-SH-L转基因系均表现出细胞死亡延迟，但PR1a-SH-L转基因系没有。我们认为，SH-L的表型表明早期SA积累是通过可能包括影响宿主细胞死亡速率以及可能对病毒功能产生影响的机制来防止病毒逃逸的主要因素。
