The Coat Protein and NIa Protease of Two Potyviridae Family Members Independently Confer Superinfection Exclusion.
Superinfection exclusion (SIE) is an antagonistic virus-virus interaction whereby initial infection by one virus prevents subsequent infection by closely related viruses. Although SIE has been described in diverse viruses infecting plants, humans, and animals, its mechanisms, including involvement of specific viral determinants, are just beginning to be elucidated. In this study, SIE determinants encoded by two economically important wheat viruses, Wheat streak mosaic virus (WSMV; genus Tritimovirus, family Potyviridae) and Triticum mosaic virus (TriMV; genus Poacevirus, family Potyviridae), were identified in gain-of-function experiments that used heterologous viruses to express individual virus-encoded proteins in wheat. Wheat plants infected with TriMV expressing WSMV P1, HC-Pro, P3, 6K1, CI, 6K2, NIa-VPg, or NIb cistrons permitted efficient superinfection by WSMV expressing green fluorescent protein (WSMV-GFP). In contrast, wheat infected with TriMV expressing WSMV NIa-Pro or coat protein (CP) substantially excluded superinfection by WSMV-GFP, suggesting that both of these cistrons are SIE effectors encoded by WSMV. Importantly, SIE is due to functional WSMV NIa-Pro or CP rather than their encoding RNAs, as altering the coded protein products by minimally changing RNA sequences led to abolishment of SIE. Deletion mutagenesis further revealed that elicitation of SIE by NIa-Pro requires the entire protein while CP requires only a 200-amino-acid (aa) middle fragment (aa 101 to 300) of the 349 aa. Strikingly, reciprocal experiments with WSMV-mediated expression of TriMV proteins showed that TriMV CP, and TriMV NIa-Pro to a lesser extent, likewise excluded superinfection by TriMV-GFP. Collectively, these data demonstrate that WSMV- and TriMV-encoded CP and NIa-Pro proteins are effectors of SIE and that these two proteins trigger SIE independently of each other.


OBJECTIVE
Superinfection exclusion (SIE) is an antagonistic virus-virus interaction that prevents secondary invasions by identical or closely related viruses in the same host cells. Although known to occur in diverse viruses, SIE remains an enigma in terms of key molecular determinants and action mechanisms. In this study, we found that Wheat streak mosaic virus (WSMV) and Triticum mosaic virus (TriMV) encode two independently functioning cistrons that serve as effectors of SIE at the protein but not the RNA level. The coat protein and NIa-Pro encoded by these two viruses, when expressed from a heterologous virus, exerted SIE to the cognate viruses. The identification of virus-encoded effectors of SIE and their transgenic expression could potentially facilitate the development of virus-resistant crop plants. Additionally, functional conservation of SIE in diverse virus groups suggests that a better understanding of the underlying mechanisms of SIE could facilitate the development of novel antiviral therapies against viral diseases.
United States Department of Agriculture-Agricultural Research Service and Department of Plant Pathology, University of Nebraska-Lincoln, Lincoln, Nebraska, USA satya.tatineni@ars.usda.gov.
Satyanarayana
S
Tatineni
United States Department of Agriculture-Agricultural Research Service and Department of Plant Pathology, University of Nebraska-Lincoln, Lincoln, Nebraska, USA.
Roy
R
French
D000595:Amino Acid Sequence; D036022:Capsid Proteins / Q000235:genetics / Q000502:physiology; D010450:Endopeptidases / Q000235:genetics / Q000502:physiology; D016679:Genome, Viral; D010935:Plant Diseases / Q000821:virology*; D030821:Plants, Genetically Modified; D019176:Potyviridae / Q000235:genetics / Q000472:pathogenicity* / Q000502:physiology*; D015163:Superinfection / Q000821:virology; D014908:Triticum / Q000235:genetics / Q000821:virology*; D014764:Viral Proteins / Q000235:genetics / Q000502:physiology
D036022:Capsid Proteins; D014764:Viral Proteins; D010450:Endopeptidases; C059992:nuclear inclusion protein a, mosaic viruses
J Virol. 2007 May;81(9):4591-603
17301154
Virology. 1990 Jul;177(1):375-9
2162110
J Virol. 2005 Sep;79(18):12077-80
16140783
Trends Genet. 2006 May;22(5):268-80
16567016
J Virol. 1985 May;54(2):351-7
3989908
Virology. 1978 Mar;85(1):1-8
644880
J Virol. 2007 Apr;81(8):3693-703
17287280
Phytopathology. 1998 Aug;88(8):782-7
18944883
Transgenic Res. 2006 Oct;15(5):527-41
16838196
Science. 2001 Jun 22;292(5525):2277-80
11423650
Nat Rev Genet. 2013 Feb;14(2):100-12
23329111
J Virol. 1974 Nov;14(5):1076-82
4473566
J Virol. 2012 May;86(10):5554-61
22398285
Phytopathology. 1999 Dec;89(12):1182-5
18944643
Phytopathology. 2006 Mar;96(3):320-5
18944448
Plant J. 2000 Aug;23(4):547-55
10972881
Adv Virus Res. 2015;92:101-99
25701887
Curr Opin Virol. 2014 Dec;9:119-26
25462443
Mol Plant Microbe Interact. 2002 Jul;15(7):683-92
12118884
Virology. 1998 Sep 1;248(2):188-98
9721228
Virology. 2008 Jul 5;376(2):297-307
18456299
J Virol. 1997 Sep;71(9):7119-23
9261447
EMBO J. 1997 Aug 1;16(15):4738-45
9303318
J Bacteriol. 1952 Feb;63(2):209-17
14938301
Cell. 2000 Sep 29;103(1):157-67
11051555
Virology. 1968 Jul;35(3):395-407
5662869
J Virol. 2014 Sep 1;88(17):9751-68
24920806
J Virol Methods. 2013 Apr;189(1):196-203
23454646
Virology. 2006 Jul 5;350(2):465-74
16540139
Plant Cell. 2002;14 Suppl:S289-301
12045284
Proc Natl Acad Sci U S A. 1993 Aug 15;90(16):7513-7
8356047
Philos Trans R Soc Lond B Biol Sci. 1999 Mar 29;354(1383):659-64
10212946
J Virol. 2005 Mar;79(6):3231-42
15731218
Phytopathology. 2009 Aug;99(8):943-50
19594313
Curr Opin Microbiol. 2016 Aug;32:82-88
27253151
J Virol. 2008 Aug;82(16):7988-99
18550675
Virology. 1997 Apr 28;231(1):59-71
9143303
J Neurovirol. 2007 Aug;13(4):353-63
17849319
J Virol. 2014 Jan;88(2):1366-80
24227854
Virology. 1970 Nov;42(3):773-6
5483266
J Bacteriol. 2012 Sep;194(18):5012-9
22797755
Virology. 1966 Aug;29(4):642-53
4287699
J Virol. 2011 Feb;85(4):1718-31
21147925
Mol Plant Microbe Interact. 2014 Feb;27(2):150-62
24111920
Retrovirology. 2005 Aug 18;2:52
16107223
J Bacteriol. 1953 Sep;66(3):247-53
13096470
Plant Dis. 2014 Jun;98(6):806-810
30708632
Virology. 1982 May;119(1):150-8
18635142
Genes Dev. 2006 Apr 1;20(7):759-71
16600909
Virology. 2011 Feb 5;410(1):268-81
21145088
Plant Cell. 1999 Jul;11(7):1207-16
10402423
Annu Rev Phytopathol. 2015;53:45-66
25938276
Plant Dis. 2009 Jan;93(1):25-29
30764256
Virology. 2001 Apr 10;282(2):230-6
11289805
J Virol. 2010 Feb;84(3):1314-25
19923189
Phytopathology. 2010 Mar;100(3):230-8
20128696
J Virol. 2013 Dec;87(24):13354-69
24089557
Arch Virol. 2009;154(9):1511-5
19649764
Mol Plant Microbe Interact. 2016 Sep;29(9):724-738
27551888
J Gen Virol. 1991 Apr;72 ( Pt 4):791-9
2016594
J Virol. 2005 Jul;79(14):9054-61
15994799
Science. 1997 Jun 6;276(5318):1558-60
18610513
Trends Genet. 2001 Aug;17(8):449-59
11485817
Virology. 2016 Feb;489:108-15
26748332
Virology. 1983 Nov;131(1):137-43
6316647
Phytopathology. 2015 Nov;105(11):1496-505
26214124
J Virol. 2009 Nov;83(22):11765-76
19726510
Mol Plant Pathol. 2016 Jun;17(5):769-82
26416204
Mol Plant Pathol. 2012 Feb;13(2):204-16
21726401
Nat Commun. 2010;1:146
21266996