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

转基因烟草对黄瓜花叶病毒(CMV)的抗性受以下几个因素的影响：1)温度升高(30-32℃)时，CP对CMV敏感，但CP内源外壳蛋白的积累水平在30-32℃时较常温(23-27℃)有所下降，但对外壳蛋白mRNA的积累影响不大。2)CP对不同CMV无卫星RNA(sat-RNA)株系的侵染表现出不同的敏感性。CP对CMV的F、P株系比Y株系更敏感，Y株系利用外壳蛋白基因获得转基因烟草植株。3)在供试的任何CMV株系中，CP对不含Sat-RNA的CMV比对含有Sat-RNA的CMV更敏感。这些结果表明，接种病毒粒子的外壳蛋白不是CP对CMV抗性的直接决定因素，CP对CMV的抗性受CMV的生物学特性的影响，包括RNA1、RNA2和CMV 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.