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Short description of Impatiens necrotic spot virus genome

Last update on the 12th of October, 2016

Impatiens necrotic spot virus (INSV) is a plant pathogenic virus of the Bunyaviridae family, genus Tospovirus, very similar to another Tospovirus, Tomato spotted wilt virus (TSWV). It is spread by the insect vector, western flower thrips (Frankliniella occidentalis), and infects more than 648 plant species, including important agricultural plants such as tomatoes, lettuce, pepper[1] and ornamentals. The countries in which INSV occures are the EU, Israel, the USA, Canada and Costa Rica[2]. Table 1 presents some main qualitative and quantitative properties that characterizes INSV.

Table 1. Main INSV genome properties
Attribute Value
English virus name Impatiens necrotic spot virus
Russian virus name Вирус некротической пятнистости Недотроги
Number of segments in full genome 3
Full genome length, bp 16740
Number of encoded polypeptides 5
Number of mature virus proteins 6

Genome organisation

The INSV has a single stranded RNA tripartate genome of S, M and L segments. The main L RNA (in negative sense) translation product (L protein) presents a putative RNA-dependent RNA polymerase with estimated mass of 330.3 kDa[3]. The M RNA has an ambisense organisation: a smaller open reading frame (ORF) in the viral sense encodes a nonstructual protein (NSm, 34 kDa)[4], whereas bigger ORF in the viral complementary sense encodes a polypeptide with a predicted molecular weight of 124.9 kDa, which then is modified into G1 and G2 proteins[5]. S RNA molecule is also ambisense and encodes a non-structural protein (NSs, 51 kDa)[6] in the viral sense and a nucleocapsid protein (N, 28.6 kDa)[7](fig. 1) in the viral complementary sense[8].

Fig. 1. Aminoacid sequence of the shortest INSV protein in .fasta format
>NP_619709.1 nucleocapsid protein [Impatiens necrotic spot virus]
MNKAKITKENIVKLLTQSDSLEFEETQNEGSFNFTDFFTNNREKIQNMTTASCLSFLKNR
QSIMRVIKSADFTFGSVTIKKTRNNSERVGVNDMTFRRLDAMVRVHLVGMIKDNGSALTE
AINSLPSHPLIASYGLATTDLKSCVLGVLLGGSLPLIASVLNFEIAALVPAIYQDAKHVE
LGIDMSKFSTKEAVGKVCTVLKSKGYSMNSVEIGKAKQYADILKACSPKAKGLAAMDHYK
EGLTSIYSMFNATIDFGKNDSI

Biology

INSV virions are similar to TSWV ones[2]: they are spherical enveloped particles, about 70-110 nm in diameter, which contain an internal N protein binded to RNA molecules, two membrane glycoproteins (G1 and G2), and a large (L) protein[9] presenting putative polymerase, which also may be binded to ribonucleoprotein complex (fig. 2). Each segment exhibits a pseudo-curcular structure due to complementary ends[10].

Fig. 2. Schematic cross-section of a Bunyaviridae virion[11]

The insect vector, thrips, contains virions, which get into the plant with digged vector. Then ssRNA injects itself into the host cell, where it replicates and, being disguised by N protein, moves through the plant over enlarged plasmodesmata. The virus can also infect other plants by the insect vector, that will start the cycle again[1].

The main symptom, as virus name implies, is necrotic spots (often with a surrounding halo) that appear on the leaves. Also lamina curves downward, stem yellows and dies[1](see fig.3).

INSV.JPG
Fig 3. The INSV on fuschia[12]

References

  1. INSV article on Wikipedia;
  2. European and Mediterranean plant protection organisation data sheets on qurantine pests, INSV;
  3. van Poelwijk F, Prins M, Goldbach R, Completion of the impatiens necrotic spot virus genome sequence and genetic comparison of the L proteins within the family Bunyaviridae, Journal of general virology, March 1997 78: 543-546, doi: 10.1099/0022-1317-78-3-543;
  4. NCBI Reference Sequence: NP_619690.1;
  5. M.D. Law, J. Speck, J.W. Moyer, The M RNA of impatiens necrotic spot Tospovirus (Bunyaviridae) has an ambisense genomic organization, Virology, 1992, Elsevier, doi:10.1016/0042-6822(92)90528-W;
  6. NCBI Reference Sequence: NP_619708.1;
  7. NCBI Reference Sequence: NP_619709.1;
  8. Peter de Haan, Antonio C. de Avila, Richard Kormelink, Annemarie Westerbroek, Jan J.L. Gielen, Dick Peters, Rob Goldbach, The nucleotide sequence of the S RNA of Impatiens necrotic spot virus, a novel tospovirus, FEBS letters, 306: 27–32, doi: 10.1016/0014-5793(92)80830-A;
  9. European and Mediterranean plant protection organisation data sheets on qurantine pests, TSWV;
  10. Family Bunyaviridae article on Wikipedia;
  11. Ramon Flick, Chris A. Whitehouse, Crimean-Congo Hemorrhagic Fever Virus, Current Molecular Medicine, 5(8):753-60, doi: 10.2174/156652405774962335;
  12. Image credits on Wikimedia.