Tomato chlorosis virus infection represses chloroplast related genes in tomato.

Tomato chlorosis virus (ToCV) causes mild to severe chlorosis on tomato leaves. Although it has been postulated that chlorosis is caused by changes in biosynthesis, degradation, function and/or structure of chlorophyll, mechanisms of virus-induced chlorosis has not been explored to date. To understand the mechanisms of virus induced chlorosis, ToCV-tomato interaction was studied at transcriptome level using suppression subtractive hybridization (SSH) followed by macroarray hybridization and RT-qPCR. First, a susceptible tomato cultivar, MoneyMaker was graft-inoculated with ToCV. Next, cDNAs were synthesized from mRNAs of leaf samples from ToCV-inoculated and mock-inoculated control plants at 30-day of post inoculation (dpi). Then, a cDNA library enriched with ToCV-repressed genes was constructed using SSH. 250 randomly selected clones from library were sequenced and the expressions of 140 genes were determined by nylon macroarray hybridizations. The expression of 119 genes were significantly decreased by 1.5 or greater fold in response to ToCV infection. The expressions of many genes involved in transcription, defense response, metabolism, and photosynthesis, signaling and protein fate were repressed upon infection with ToCV. The genes repressed by ToCV in tomato were mostly associated with organelles, especially with the chloroplast. After expression analysis of 40 selected ToCV-repressed genes by RT-qPCR assay, the repression of 37 genes in response to ToCV infection was confirmed. Furthermore, a detail expression analysis of ferredoxin 2 (Fd2) gene between 0 dpi and 45 dpi in ToCV-inoculated and mock-inoculated control plants showed that the expression of Fd-2 gene was significantly repressed at 8 to 30 dpi in ToCV-infected plants.