Abstract
A number of phloem-limited viruses induce the development of tumours (enations) in the veins of host plants, but the relevance of tumour induction to the life cycle of those viruses is unclear. In this study, we performed molecular and structural analyses of tumours induced by rice black-streaked dwarf virus (RBSDV, genus Fijivirus) infection in maize plants. The transcript level of the maize cdc2 gene, which regulates the cell cycle, was highly elevated in tumour tissues. Two-dimensional electrophoresis identified 25 cellular proteins with altered accumulation in the tumour tissues. These proteins are involved in various metabolic pathways, including photosynthesis, redox, energy pathways and amino acid synthesis. Histological analysis indicated that the tumours predominantly originated from hyperplastic growth of phloem, but those neoplastic tissues have irregular structures and cell arrangements. Immunodetection assays and electron microscopy observations indicated that in the shoots, RBSDV is confined to phloem and tumour regions and that virus multiplication actively occurs in the tumour tissue, as indicated by the high accumulation of non-structural proteins and formation of viroplasms in the tumour cells. Thus, the induction of tumours by RBSDV infection provides a larger environment that is favourable for virus propagation in the host plant.
Highlights
On tumour tissue induced by Rice black-streaked dwarf virus (RBSDV) were mainly based on observation using high resolution electron microscopy[13,26,27]; the comprehensive view of the structural anatomy, cell composition and virus distribution of this highly proliferated tissue is still limited
To obtain the experimental materials, maize plants infected with RBSDV were collected from field experimental plots, and the presence of the virus was confirmed by RT-PCR
To further gain insight into the physiological changes that occur in the tumour tissue, we investigate the cellular proteins with altered accumulation in the tumour tissue induced by RBSDV using two-dimensional electrophoresis (2-DE) analysis comparing total proteins extracted from the tumour portion and vein of uninfected leaves
Summary
On tumour tissue induced by RBSDV were mainly based on observation using high resolution electron microscopy[13,26,27]; the comprehensive view of the structural anatomy, cell composition and virus distribution of this highly proliferated tissue is still limited. To gain insight into the physiological basis underlying the tumour formation, it is important to investigate the cellular proteins with differentially altered expression in the tumour tissue. To address the abovementioned issues, in this study, we performed both histological and proteomic analyses of tumour tissues in RBSDV-infected maize plants. Our analyses indicated a vascular origin of the tumour cells and identified several cellular proteins that are either up- or down-regulated in tumour tissues. We observed that tumour tissues contain the highest accumulation of RBSDV. The significance of tumours as the multiplication sites of RBSDV is discussed
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