ULTRASTRUCTURE OF MAIZE NECROTIC STREAK VIRUS INFECTIONS

Authors: DE STRADIS, A - NAT. RES. COUNCIL, ITALY; Redinbaugh, Margaret; Abt, John; MARTELLI, G - NAT. RES. COUNCIL, ITALY

Submitted to: Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2005
Publication Date: 11/1/2005
Citation: De Stradis, A., Redinbaugh, M.G., Abt, J.J., Martelli, G.P. 2005. Ultrastructure of maize necrotic streak virus infections. Journal of Plant Physiology. 87:213-221.

Interpretive Summary: Maize fine streak virus (MNeSV) was recently isolated and characterized by USDA and collaborating scientists. The sequence of the viral genome, shape of the virus particles and soil transmission indicated the virus was most closely related to members of a virus family called Tombusviridae. However, there were some clear differences between MNeSV and other members of the family including the fact that the virus has a smaller coat protein and cannot be transmitted by rubbing a virus solution on maize leaves. Because other members of the Tombusviridae cause the formation of characteristic 'multivesicular bodies' in infected plant leaves, cells from MNeSV-infected maize leaves were examined for the presence of these bodies using electron microscopy. MNeSV infection produced several distinctive changes in maize cells: 1) virus particles accumulated to high levels in cell cytoplasm and sometimes in intercellular spaces of infected plants; 2) infected cells shrunk dramatically and contained amorphous, darkly-stained material; and, 3) cellular membranes proliferated and formed lots of vesicles in infected cells.Although these features were distinctive, they were significantly different than those found in plants infected with other Tombusviridae viruses. These results will aid scientists who study and classify plant viruses in this family in understanding the evolutionary pathological relationships among the viruses. This work will be used by research scientists to understand the relationships among viruses that are important disease causing agents in crops. Understanding these relationships is critical to developing diagnostic tools and strategies for control.

Technical Abstract: Maize necrotic streak virus (MNeSV) has 32 nm isometric particles that encapsidate a single stranded RNA genome ca. 4.3 kb in size, and is a tentative member of the genus Tombusvirus. Since tombusviruses elict the formation of cytopathological structures knowm as "multivesicular bodies" that assist in their classification at the genus level, the cytology of thin-sectioned maize leaf tissues 7, 15, and 45 days after inoculation was investigated. The prominent cytopathological features were: (i) an extensive accumulation of virus particles scattered throughout the cytoplasm or in crystalline arrays in the cytoplasm or, occasionally, in intercelluar spaces; (ii) extensive plasmolysis and the appearance of small patches of amorphous, dark-staining material in the cytoplasm; (iii) the proliferation of membranes and the presence of empty double membrane-bound vesicular structures of various sizes. No apparent connection between these membranous elements and the nuclear envelope was detected, even when large clusters of vesicles were adpressed to the nuclei. Some of the largest double-membrane bound structures had rows of small vesicles located inside peripheral dilations of the bounding membrane. Although most of these structures appeared to originate from disintegrating mitochondria, they bore little resemblance to genuine multivesicular bodies like those arising from the modified mitochondria that follow infection by certain members of the family Tombusviridae, i.e., Carnation Italian ringspot virus, Pelargonium necrotic spot virus (PNSV), Galinsoga mosaic virus (GaMV), and Turnip crinkle virus (TCV). Immunogold labelling using antibodies to virus particles was detected over cytoplasm associated with virus particles and patches of electron-dense amorphous material, suggesting that this material consists of virus coat protein.