Nucleotide sequence of the S and M RNA segments of a Groundnut bud necrosis virus isolate from Vigna radiata in India

Exposure to watermelon bud necrosis virus and groundnut bud necrosis virus alters the life history traits of their vector, Thrips palmi (Thysanoptera: Thripidae)

Thrips palmi transmits the tospoviruses watermelon bud necrosis (WBNV) and groundnut bud necrosis virus (GBNV) in persistent propagative way. Little is known about the T. palmi-WBNV and -GBNV relationship. In this study, we report the effects of WBNV and GBNV infection on the life history traits of T. palmi. Both WBNV and GBNV had some negative effects on the adult life span, fecundity and survival of T. palmi as compared to non-exposed T. palmi. Tospovirus exposure favoured a female-biased ratio in the experimental population.

Interference in plant defense and development by non-structural protein NSs of Groundnut bud necrosis virus

Groundnut bud necrosis virus (GBNV) infects a large number of leguminous and solanaceous plants. To elucidate the biological function of the non-structural protein encoded by the S RNA of GBNV (NSs), we studied its role in RNA silencing suppression and in viral pathogenesis. Our results demonstrated that GBNV NSs functions as a suppressor of RNA silencing using the agroinfiltration patch assay. An in silico analysis suggested the presence of pro-apoptotic protein Reaper-like sequences in the GBNV NSs, which were known to be present in animal infecting bunyaviruses. Utilizing NSs mutants, we demonstrated that a Leu-rich domain was required for RNA silencing suppression activity, but not the non-overlapping Trp/GH3 motif of the Reaper-like sequence. To investigate the role of NSs in symptom development we generated transgenic tomato expressing the GBNV NSs and showed that the expression of NSs in tomato mimics symptoms induced by infection with GBNV, such as leaf senescence and necrosis. As leaf senescence is controlled by miR319 regulation of the transcription factor TCP1, we assessed the accumulation of both RNAs in transgenic NSs-expressing and GBNV-infected tomato plants. In both types of plants the levels of miR319 decreased, while the levels of TCP1 transcripts increased. We propose that GBNV-NSs affects miRNA biogenesis through its RNA silencing suppressor activity and interferes with TCP1-regulated leaf developmental pathways.

Importance and genetic diversity of vegetable-infecting tospoviruses in India

A survey for Peanut bud necrosis virus (PBNV), Watermelon bud necrosis virus (WBNV), Capsicum chlorosis virus (CaCV), and Iris yellow spot virus (IYSV) was conducted between 2002 and 2009 in the major vegetable-growing areas in India. PBNV was documented widely in tomato and chili peppers in 14 states representing southern, north-western, north-eastern, and central regions and WBNV was predominantly detected in watermelons and cucurbits in all except north-eastern regions. In addition, the expanded host range of PBNV to watermelons and other cucurbits and WBNV to tomato and chili peppers was observed leading to natural mixed infection of the two viruses. IYSV was found in onion in southern, central, and north-eastern regions and CaCV in tomato and chili peppers in northern and southern regions, respectively. Phylogenetic analysis of the nucleocapsid gene revealed segregation of field isolates of PBNV and WBNV into two distinct subclades, whereas isolates of CaCV and IYSV each clustered into a single clade. A proposal for establishing WBNV as a distinct tospovirus species is made based on the molecular characterization of small- (S) and medium- (M) RNA segments.

Biological and molecular characterization of Capsicum chlorosis virus infecting chilli and tomato in India

Two isolates of Capsicum chlorosis virus (CaCV, genus Tospovirus) from tomato (CaCV-To-Ind) and chilli (CaCV-Ch-Pan), collected from Haryana and Uttar Pradesh states of northern India respectively, were compared. A comparison of the amino acid sequences of their N genes revealed more than 96% identity, confirming that the virus isolates in India have a high degree of sequence conservation and are closely related to Australian isolates. Analysis of the host range of CaCV revealed no biological difference between the isolates, but they differed from CaCV-Australia. The nucleotide sequences of S, M and L RNA of CaCV-Ch-Pan were determined. The S RNA contains 3,105 nucleotides (nt), with NSs and N genes of 1,320 and 828 nt, respectively. The M RNA consists of 4,821 nt, with an NSm gene of 927 nt and a Gn/Gc gene of 3,366 nt. The intergenic regions of S and M RNA contain 824 and 425 nt, respectively. The L RNA consists of 8,912 nt, with an RNA-dependent RNA polymerase gene of 8,634 nt.

Structure and genome organization of the large RNA of iris yellow spot virus (genus Tospovirus, family Bunyaviridae)

The structure and organization of the large (L) RNA of iris yellow spot virus (IYSV) was determined, and with this report, the complete genomic sequence of IYSV of the genus Tospovirus, family Bunyaviridae has been elucidated. The L RNA of IYSV was 8,880 nucleotides in length and contained a single open reading frame in the viral complementary (vc) strand. The primary translation product of 331.17 kDa shared many of the features of the viral RNA-dependent RNA polymerase (RdRp) coded by L RNAs of known tospoviruses. The 5' and 3' termini of IYSV L RNA (vc) contain two untranslated regions of 33 and 226 nucleotides, respectively, and both termini have conserved terminal nucleotides, another common feature of tospovirus genomic RNAs. Conserved motifs characteristic of RdRps of members of the family Bunyaviridae were present in the IYSV RdRp.

Nucleotide sequence and genome organization of the medium RNA of Iris yellow spot virus from the United States

Iris yellow spot tospovirus (IYSV) of the family Bunyaviridae causes a serious disease in onion in the USA and other parts of the world. Inspite of its economic importance, the complete genomic sequence of IYSV from the USA is not available. The genome structure and organization of the medium (M) RNA of a Washington (WA) isolate of IYSV were determined and compared to the corresponding region of two isolates previously described from Brazil and The Netherlands. Sequence analysis showed that the M-RNA was 4,817 nucleotides long and potentially coded for the movement protein (NSm) in the viral sense and the glycoprotein precursor (Gn and Gc) in the viral complementary sense. The predicted sizes of NSm and Gn/Gc precursor were 34.7 and 128.84 kDa, respectively. The two open reading frames are separated by a 380 nucleotide intergenic region. Phylogenetic analysis of the NSm and Gn/Gc genes from the WA isolate showed grouping that reflected their respective serogroups. The WA isolate formed a close cluster with the two previously reported IYSV isolates and the IYSV cluster was distinguishable from other tospovirus species. This is the first report of complete genomic sequence of the M-RNA of IYSV from the US.