Abstract
Upon virus infections, the rapid and comprehensive transcriptional reprogramming in host plant cells is critical to ward off virus attack. To uncover genes and defense pathways that are associated with virus resistance, we carried out the transcriptome-wide Illumina RNA-Seq analysis of pepper leaves harboring the L3 resistance gene at 4, 8, 24 and 48 h post-inoculation (hpi) with two tobamoviruses. Obuda pepper virus (ObPV) inoculation led to hypersensitive reaction (incompatible interaction), while Pepper mild mottle virus (PMMoV) inoculation resulted in a systemic infection without visible symptoms (compatible interaction). ObPV induced robust changes in the pepper transcriptome, whereas PMMoV showed much weaker effects. ObPV markedly suppressed genes related to photosynthesis, carbon fixation and photorespiration. On the other hand, genes associated with energy producing pathways, immune receptors, signaling cascades, transcription factors, pathogenesis-related proteins, enzymes of terpenoid biosynthesis and ethylene metabolism as well as glutathione S-transferases were markedly activated by ObPV. Genes related to photosynthesis and carbon fixation were slightly suppressed also by PMMoV. However, PMMoV did not influence significantly the disease signaling and defense pathways. RNA-Seq results were validated by real-time qPCR for ten pepper genes. Our findings provide a deeper insight into defense mechanisms underlying tobamovirus resistance in pepper.
Highlights
Upon virus infections, the rapid and comprehensive transcriptional reprogramming in host plant cells is critical to ward off virus attack
Pepper mild mottle virus (PMMoV) was able to spread into the whole plant, the infection became systemic without any visible disease symptoms according to earlier results
The closest pepper homolog of NaERF2 was identified in our studies as a strongly Obuda pepper virus (ObPV)-inducible ethylene-responsible transcription factors (ERFs) gene (CaERF1A/XM_016714653), Supplementary Table S5). These results show that capsidiol biosynthesis may be transcriptionally regulated by an ERF transcription factor in ObPV-inoculated pepper leaves
Summary
The rapid and comprehensive transcriptional reprogramming in host plant cells is critical to ward off virus attack. The complete pepper genome has recently been sequenced by three independent research teams providing detailed genetic information of about 35,000 pepper genes arranged on 12 c hromosomes[27,28,29] These novel pepper genetic databases allow the use of transcriptome-wide, high performance analytical methods like RNA-Seq in virus-infected pepper leaves. This unbiased approach can provide genuinely novel information about defense genes and regulatory m echanisms[26,30]. No transcriptome-wide analysis has been carried out yet with ObPV
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