Quantitative transcriptional changes associated with chlorosis severity in mosaic leaves of tobacco plants infected with Cucumber mosaic virus.

Cucumber mosaic virus (CMV) causes mosaic disease in inoculated tobacco plants. Coat protein (CP) is one of the major virulence determinants of CMV, and an amino acid substitution at residue 129 in CP alters the severity of chlorosis, such as pale green chlorosis and white chlorosis, in symptomatic tissues of mosaic leaves of infected tobacco. In this study, we compared the transcriptomes of chlorotic tissues infected with the wild-type pepo strain of CMV and two strains carrying CP mutants with diverse chlorosis severity. Differential gene expression analysis showed that CMV inoculation appeared to have similar effects on the transcriptional expression profiles of the symptomatic chlorotic tissues, and only the magnitude of expression differed among the different CMVs. Gene ontology analysis with biological process and cellular component terms revealed that many nuclear genes related to abiotic stress responses, including responses to cadmium, heat, cold and salt, were up-regulated, whereas chloroplast- and photosynthesis-related genes (CPRGs) were down-regulated, in the chlorotic tissues. Interestingly, the level of CPRG down-regulation was correlated with the severity of chlorosis. These results indicate that CP mutation governs the repression level and mRNA accumulation of CPRGs, which are closely associated with the induction of chlorosis.