ABSTRACT
The purpose of the study was to investigate the role of salicylic acid (SA) signalling in Ny-1-mediated hypersensitive resistance (HR) of potato (Solanum tuberosum L.) to Potato virus Y (PVY). The responses of the Ny-1 allele in the Rywal potato cultivar and transgenic NahG-Rywal potato plants that do not accumulate SA were characterized at the cytological, biochemical, transcriptome, and proteome levels. Analysis of noninoculated and inoculated leaves revealed that HR lesions started to develop from 3 d post inoculation and completely restricted the virus spread. At the cytological level, features of programmed cell death in combination with reactive oxygen species burst were observed. In response to PVY infection, SA was synthesized de novo. The lack of SA accumulation in the NahG plants led to the disease phenotype due to unrestricted viral spreading. Grafting experiments show that SA has a critical role in the inhibition of PVY spreading in parenchymal tissue, but not in vascular veins. The whole transcriptome analysis confirmed the central role of SA in orchestrating Ny-1-mediated responses and showed that the absence of SA leads to significant changes at the transcriptome level, including a delay in activation of expression of genes known to participate in defence responses. Moreover, perturbations in the expression of hormonal signalling genes were detected, shown as a switch from SA to jasmonic acid/ethylene signalling. Viral multiplication in the NahG plants was accompanied by downregulation of photosynthesis genes and activation of multiple energy-producing pathways.
Subject(s)
Plant Diseases/immunology , Plant Proteins/genetics , Potyvirus/physiology , Salicylic Acid/metabolism , Solanum tuberosum/genetics , Transcriptome , Apoptosis , Cyclopentanes/metabolism , Down-Regulation , Energy Metabolism , Ethylenes/metabolism , Gene Expression Regulation, Plant , Host-Pathogen Interactions , Oxylipins/metabolism , Photosynthesis , Plant Diseases/virology , Plant Growth Regulators/metabolism , Plant Immunity , Plant Leaves/genetics , Plant Leaves/immunology , Plant Leaves/virology , Plant Proteins/metabolism , Reactive Oxygen Species/metabolism , Signal Transduction , Solanum tuberosum/immunology , Solanum tuberosum/virologyABSTRACT
The distribution of Potato virus Y (PVY) in the systemically infected potato (Solanum tuberosum) plants of the highly susceptible cultivar Igor was investigated. Virus presence and accumulation was analyzed in different plant organs and tissues using real-time polymerase chain reaction and transmission electron microscopy (TEM) negative staining methods. To get a complete insight into the location of viral RNA within the tissue, in situ hybridization was developed and optimized for the detection of PVY RNA at the cellular level. PVY was shown to accumulate in all studied leaf and stem tissues, in shoot tips, roots, and tubers; however, the level of virus accumulation was specific for each organ or tissue. The highest amounts of viral RNA and viral particles were found in symptomatic leaves and stem. By observing cell ultrastructure with TEM, viral cytoplasmic inclusion bodies were localized in close vicinity to the epidermis and in trichomes. Our results show that viral RNA, viral particles, and cytoplasmic inclusion bodies colocalize within the same type of cells or in close vicinity.
Subject(s)
Plant Diseases/virology , Potyvirus/metabolism , Solanum tuberosum/virology , Biological Transport , In Situ Hybridization , Microscopy, Electron, Transmission , Organ Specificity , Plant Epidermis/ultrastructure , Plant Epidermis/virology , Plant Leaves/ultrastructure , Plant Leaves/virology , Plant Roots/ultrastructure , Plant Roots/virology , Plant Stems/ultrastructure , Plant Stems/virology , Potyvirus/genetics , Potyvirus/ultrastructure , RNA, Viral/genetics , Reverse Transcriptase Polymerase Chain Reaction , Solanum tuberosum/ultrastructure , Virion/genetics , Virion/metabolism , Virion/ultrastructureABSTRACT
Potato virus Y (PVY) has a worldwide distribution and infects several economically important crops from the Solanaceae family. The emergence and spread of the PVYNTN strain, which is the causative agent of potato tuber necrotic ringspot disease (PTNRD), has lead to large economic losses and highlighted the need for accurate discrimination of the different PVY strains. Detection and differentiation of PVY isolates is mainly based on a combination of ELISA, RT-PCR and bioassays; however, PVYNTN isolates are particularly difficult to differentiate from standard PVYN without the use of time-consuming bioassays. A strong correlation has been identified previously between the ability to induce PTNRD and the presence of a recombination point in the virus coat protein. An RT real-time PCR assay has been developed to enable detection of isolates with the recombination point, therefore, enabling rapid differentiation between potentially tuber necrotic PVYNTN isolates and standard PVYN isolates. The assay is also able to detect the presence of PVYO isolates. To aid with routine testing, immuno-capture and post-ELISA virus release were introduced; when coupled with RT real-time PCR the sensitivity of the assays were up to seven orders of magnitude higher than ELISA. The assay was shown to be a suitable method for rapid large-scale diagnostic testing of PVY in different types of plant material including tubers, and specific screening for potentially tuber necrotic recombinant isolates.
