Polidoros A N, Mylona P V, Scandalios J G
Department of Genetics, North Carolina State University Raleigh, 27695-7614, USA.
Transgenic Res. 2001 Dec;10(6):555-69. doi: 10.1023/a:1013027920444.
Transgenic tobacco genotypes expressing the maize Cat2 gene were developed with altered catalase (CAT) levels that resulted in a moderate increase of CAT activity in two transgenic lines. Bacterial infection, with a pathogen that does not share homology with the transgene, caused local and systemic down-regulation of the steady state mRNA levels of the 35S-driven transgene in a manner resembling post-transcriptional gene silencing (PTGS). Phenotypic symptoms of hypersensitive response (HR) and systemic acquired resistance (SAR) were similar in control SR1 and the transgenic genotypes. Induction of hin1, used as a molecular marker of plant responses to invading bacteria, displayed a similar pattern between control and transgenic lines, but some variation in the levels of expression was observed. The major difference was recorded in the ability of the plants to restrict bacterial growth during HR. All transgenic lines were more sensitive than control SR1, with two lines exhibiting a significantly reduced capacity to inhibit bacterial growth. This is consistent with the putative enhanced capacity of transgenic lines containing the maize Cat2 gene to more effectively remove H2O2, which may act as a direct antimicrobial agent. Steady state mRNA levels of PR-1 and PR-5 varied among the genotypes, possibly indicating differences in strength of the SAR signal. Transgenic line 2, which was the most sensitive during HR, was most effective in restricting bacterial growth during SAR. This indicates that a reverse correlation might exist between the severity of infection during HR and the ability to inhibit bacterial growth during SAR. Growth under high light conditions affected plant-pathogen interactions in control SR1, as well as in transgenic line 8. Early induction and higher expression of PR-1 and PR-5 was detected in both SR1 and line 8 in high light-grown plants as compared with their low light-grown counterparts. Our data indicate that growth under high light conditions can predispose plants to better resist pathogen attack, and may amplify local and systemic defense signals. Finally, one transgenic line, which exhibited 1.3-fold higher average CAT activity in comparison with the untransformed SR1 control, suffered significantly less methyl viologen (MV) damage than untransformed control plants at moderate and high MV concentrations.
通过改变过氧化氢酶（CAT）水平培育出了表达玉米Cat2基因的转基因烟草基因型，使得两个转基因株系中的CAT活性适度增加。用一种与转基因无同源性的病原体进行细菌感染，导致35S驱动的转基因的稳态mRNA水平出现局部和系统性下调，其方式类似于转录后基因沉默（PTGS）。对照SR1和转基因基因型中过敏反应（HR）和系统获得性抗性（SAR）的表型症状相似。作为植物对入侵细菌反应的分子标记的hin1的诱导，在对照和转基因株系之间显示出相似的模式，但在表达水平上观察到一些差异。主要差异记录在植物在HR期间限制细菌生长的能力上。所有转基因株系都比对照SR1更敏感，其中两个株系抑制细菌生长的能力显著降低。这与含有玉米Cat2基因的转基因株系可能具有更强的能力更有效地清除H2O2一致，H2O2可能作为一种直接的抗菌剂。PR-1和PR-5的稳态mRNA水平在不同基因型之间有所不同，这可能表明SAR信号强度存在差异。转基因株系2在HR期间最敏感，在SAR期间限制细菌生长最有效。这表明HR期间感染的严重程度与SAR期间抑制细菌生长的能力之间可能存在负相关。高光条件下的生长影响了对照SR1以及转基因株系8中的植物-病原体相互作用。与低光照生长的对应植株相比，高光生长的SR1和株系8中均检测到PR-1和PR-5的早期诱导和更高表达。我们的数据表明，高光条件下的生长可使植物更易抵抗病原体攻击，并可能放大局部和系统防御信号。最后，与未转化的SR1对照相比，一个平均CAT活性高1.3倍的转基因株系，在中等和高浓度甲基紫精（MV）处理下，遭受的MV损伤明显小于未转化的对照植株。
