Viral fitness predicts the magnitude and direction of perturbations in the infected host transcriptome

Héctor Cervera; Silvia Ambrós; Guillermo P. Bernet; Guillermo Rodrigo; Santiago F. Elena

Differences in viral fitness and host symptomatology. Table 1 shows relevant information about the seven TEV genotypes used for this study. The mutant genotypes differ from the wildtype (WT) TEV in a rather limited number of nonsynonymous mutations (1 or 2). However, their fitness values and the severity of symptoms induced differ widely. Significant differences existed among the fitness values of the seven viral genotypes chosen for this study ( Fig. 2A ; GLM likelihood ratio test: c 2 = 373.006, 6 df, P < 0.001) and among plants inoculated with the same viral genotype (c 2 = 2927.885, 14 df, P < 0.001). As a measure of the quality of data, the percentage of total variance for relative fitness explained by true genetic differences among genotypes was 70.56%, whilst differences among plants inoculated with the same viral genotype accounted for 29.16% of the observed variance. The remaining 0.28% of the observed variability was assignable to error measurements. A Bonferroni post hoc test classifies the seven genotypes into five groups (labeled as a to f in Fig. 2A) . Interestingly, the three genotypes with the lowest fitness values (AS13, CLA2 and CLA11) contain mutations in the multifunctional protein HC-Pro, whose most relevant role during infection is to serve as suppressor of the RNA-silencing (VSR) defense 40 . The two genotypes with mutations in the CI protein (PC55 and PC48), a helicase also involved in cell-to-cell movement 40 , have the mildest deleterious fitness effects.