Analysis of virus-host interaction in multiplication of tobacco mosaic virus

抗病菌株Lta1和Ltb1分别能克服番茄Tm-1和Tm-2基因赋予的抗性。为了解烟草花叶病毒（TMV）的抗性机制，并为其正常繁殖过程提供线索，测定了克服烟草花叶病毒抗性的Lta1和Ltb1突变位点。从核苷酸序列比较和随后的反向遗传分析中发现，130k/180k蛋白基因的两个碱基替换导致氨基酸从Gln（979）到Glu和从His（984）到Tyr的变化对克服Tm-1抗性的能力很重要。进一步分析其他破阻菌株和假回复剂表明，静电相互作用参与了抗性机制。原生质体的分析支持了抗性在复制过程中起作用。这与130k和180k蛋白参与复制是一致的。在Ltb1中，我们发现30k蛋白基因上的两个碱基替换导致氨基酸从Cys（868）变为Phe，从Glu（133）变为Lys，这与Ltb1克服Tm-2抗性的特性有关。由于已知30k蛋白参与细胞间运动，并且由于突变发生在30k蛋白的良好保守区域，因此Tm-2基因似乎会阻止正常的细胞间运动。对体外突变体的分析表明，外皮蛋白基因编码了具有N'基因的植物诱导超敏反应的决定因素。它不需要被组装成病毒颗粒。

Resistance-breaking strains named Lta1 and Ltb1 can overcome the resistance conferred by the Tm-1 and Tm-2 genes in tomato, respectively. To understand the resistance mechanisms and to get hints for normal process of multiplication of tobacco mosaic virus (TMV), mutations of Lta1 and Ltb1 responsible for overcoming the resistance were determined.From the nucleotide sequence comparison and subsequent reverse- genetic analysis, It was found that two base substitutions in the 130k/180k protein genes resulting in amino acid changes from Gln(979) to Glu and from His(984) to Tyr are important for the ability to overcome the Tm-1 resistance. Further analysis of other resistance-breaking strains and pseudorevertants suggested that an electrostatic interaction is involved in the resistance mechanism. Analysis in protoplasts supported that the resistance works in the course of replication. This is consistent with the involvement of the 130k and 180k proteins in replication.In the case of Ltb1, it was found that two base substitutions in the 30k protein gene resulting in amino acid changes from Cys(868) to Phe and from Glu(133) to Lys are involved in the property to overcome the Tm-2 resistance. Since the 30k protein is known to be involved in cell-to-cell movement, and since the mutations occur in well-conserved regions in the 30k protein, the Tm-2 gene would seem to block the normal cell-to-cell movement.Analysis using in vitro generated mutants revealed that the coat protein gene encodes the determinant for induction of the hypersensitive response in plants with the N' gene. It is not necessary to be assembled into virus particles.