Analysis of virus resistance mechanisms in transgenic tobacco plants expressing the coat protein gene of cucumber mosaic virus

表达黄瓜花叶病毒外壳蛋白基因（CP+）的转基因烟草对黄瓜花叶病毒（CMV）的抗性水平受以下几个因素的影响。1)在高温下（30 ~ 32℃），CP+对CMV易感。与常温（23-27℃）相比，30-32℃下CP+内源外壳蛋白积累水平降低，但外壳蛋白mRNA积累受温度影响不大。这表明外壳蛋白比该基因的mRNA更直接地参与了CP+植物的病毒抗性。2) CP+对不含卫星RNA （sat-RNA）的CMV不同毒株的感染表现出不同的敏感性。CP+对CMV F和P株的易感程度高于对CMV Y株的易感程度。3) CP+对不含Sat-RNA的CMV比含Sat-RNA的CMV更易感染。4) CP+对Y株和F株的RNA3伪重组体、F株的RNA1和Y株的rna2伪重组体的感染敏感性高于Y株。结果表明，接种病毒粒子的外壳蛋白不是CP+病毒抗性的直接决定因素，CP+病毒对CMV的抗性受到CMV生物学特性的影响，包括RNA1、2和3及其产物的相互作用。CMV外壳蛋白介导的保护机制更为复杂。

Resistance levels against infection with cucumber mosaic virus (CMV) of transgenic tobacco plants expressing the coat protein gene of CMV (CP+) were influenced by several factors as followings.1) At elevated temperature (30-32 C), CP+ became susceptible to infection with CMV.Accumulation levels of endogenous coat protein in CP+ decreased at 30-32 C compared at normal temperature (23-27 C) although accumulation of coat protein mRNA was not so much influenced by temperature. This suggested that coat protein was more directly involved in virus resistance of CP+ plants than mRNA of the gene.2) CP+ showed differential susceptibility to infection with different strains of CMV containing no satellite RNA (sat-RNA). CP+ was more susceptible to the F and the P strains of CMV than to the Y strain of CMV whose coat protein gene was used to obtain transgenic tobacco plants.3) CP+ was more susceptible to infection with sat-RNA-free CMV than CMV containing Sat-RNA in any strain of CMV tested here.4) CP+ was more susceptible to infection with psedorecombinants containing RNA3 of either the Y strain or the F strain and RNA1 and 2 of the F strain and the Y strain, respectively, than to infection with the Y strain. The results obtained here suggest that coat protein of inoculum virions was not a direct determinant for virus resistance in CP+ and that the CMV resistance in CP+ was influenced by biological properties of CMV including interaction of RNA1, 2, and 3 and their products. Mechanisms of CMV coat protein-mediated protection are more complex.