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Title: The coat protein of Alternanthera mosaic virus is the elicitor of a temperature-sensitive systemic necrosis in Nicotiana benthamiana, and interacts with a host boron transporter protein

item Lim, Hyoun-Sub
item VAIRA, ANNA MARIA - National Research Council - Italy
item BAE, HANHONG - Yeungnam University
item JANG, CHAN-YONG - Chungnam National University
item NAM, JIRYUN - Chungnam National University
item LEE, CHEOL HO - Seokyeong University
item LEE, ZEE-WON - Korea Basic Science Institute
item HWANG, JUNG ME - Korea Basic Science Institute
item KIM, HONG GI - Chungnam National University
item Roh, Mark
item Hammond, John

Submitted to: Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2014
Publication Date: 2/17/2014
Citation: Lim, H.S., Vaira, A., Bae, H., Jang, C., Nam, J., Lee, C., Lee, Z., Hwang, J., Kim, H., Roh, M.S., Hammond, J. 2014. The coat protein of Alternanthera mosaic virus is the elicitor of a temperature-sensitive systemic necrosis in Nicotiana benthamiana, and interacts with a host boron transporter protein. Virology.

Interpretive Summary: Interactions between viruses and their hosts have a variety of possible outcomes, ranging from immunity in non-hosts, through restriction of infection to the initially infected cells, to systemic infection with symptoms of varying severity. Differences in symptom severity between infections derived from distinct complementary DNA copies of the genome of Alternanthera mosaic virus (AltMV)were examined at two different temperatures. The occurrence and severity of both and systemic necrosis was found to correlate with virus replication, which was increased at 15ºC compared to 25ºC. Substitution into a necrosis-inducing isolate of the coat protein gene of an isolate that did not cause necrosis resulted in ablation of necrosis. Substitution of specific amino acid residues within the coat protein revealed two regions within the coat protein that were both necessary for the induction of necrosis; one of these regions was predicted to be on the surface of virus particles, and the other to affect interactions between neighboring coat protein subunits. A gene conferring resistance to the related Potato virus X did not prevent infection or systemic resistance, but disruption of the expression of NbSGT, which controls multiple resistance genes, resulted in reduced severity of AltMV infection. These results suggest that necrosis is caused by AltMV infection in response to a resistance gene that is currently unidentified. Increased understanding of the disease induction process may result in new means of protecting plants from virus infection.

Technical Abstract: Alternanthera mosaic virus (AltMV; Potexvirus) naturally infects several ornamental plants. Differences were previously noted between systemic symptoms induced in Nicotiana benthamiana by different isolates of AltMV, and by four infectious clones derived from AltMV-SP. Virus accumulation was enhanced at 15 ºC, and two infectious clones induced severe necrosis and plant death; high RNA copy level clone AltMV 3-7 always induced a systemic hypersensitive response (sHR) at 15 ºC. Substitution of coat protein (CP) from isolate AltMV-Po into AltMV 3-7 eliminated sHR at 15 °C. Substitution of only two AltMV-Po CP residues [MN(13,14)ID or LA(76,77)IS] was sufficient to ablate systemic necrosis. Affinity chromatography, yeast two-hybrid, and agroinfiltration experiments demonstrated that strong CP-CP interactions and relative expression level have a major influence on induction of necrotic symptoms; AltMV-SP CP, but not AltMV-Po CP, formed punctate foci in agroinfiltrated cells. Substitution mutants MN(13,14)ID (surface-located) and LA(76,77)IS (internal) differed in the degree of homologous interactions, suggesting that both aggregation of subunits and strength of interactions with a host protein influence necrosis. AltMV-induced severe necrosis at 15 ºC was not controlled by the Rx gene in transgenic N. benthamiana. AltMV symptom severity was reduced in N. benthamiana plants in which NbSGT had been silenced, suggested that the sHR caused by high concentration of CP at 15 °C was induced by a novel R gene controlled by NbSGT.