Mutation of AV2 Start Codon Impairs the Infectivity of a Bipartite Begomovirus Under High Temperature.

Squash leaf curl China virus (SLCCNV) is a bipartite Begomovirus. The function of the protein AC5, which is encoded by SLCCNV, is unknown. Here, we confirmed that the 172-amino acids (aa) long AC5 protein of SLCCNV could suppress single-stranded RNA but not double-stranded RNA-induced post-transcriptional gene silencing (PTGS). Furthermore, we determined that the C-terminal domain (96–172 aa) of the AC5 protein was responsible for RNA silencing suppressor (RSS) activity via deletion mutant analysis. The AC5 protein can reverse GFP silencing and inhibit systemic silencing of GFP by interfering with the systemic spread of the GFP silencing signal. The SLCCNV AC5 protein was localized to both the nucleus and cytoplasm of Nicotiana benthamiana cells. Furthermore, deletion analysis showed that the putative nuclear localization signal (NLS, 102–155 aa) was crucial for the RNA silencing suppression activity of AC5. In addition, the AC5 protein elicited a hypersensitive response and enhanced potoao virus X (PVX) RNA accumulation in infected N. benthamiana plants. Using the infectious clones of the SLCCNV and SLCCNV-AC5 null mutants, mutational analysis confirmed that knockout of the AC5 gene abolished SLCCNV-induced leaf curl symptoms, showing SLCCNV AC5 is also a virulence determinant.

First Report of <i>Squash leaf curl China virus</i> Associated with Mosaic and Mild Leaf Curl Disease of Pumpkin in Bangladesh

BackgroundBegomoviruses are major constraint in the production of many crops. Upon infection, begomoviruses may substantially modulate plant biological processes. While how monopartite begomoviruses interact with their plant hosts has been investigated extensively, bipartite begomoviruses-plant interactions are understudied. Moreover, as one of the major groups of hosts, cucurbitaceous plants have been seldom examined in the interaction with begomoviruses.ResultsWe profiled the zucchini transcriptomic changes induced by a bipartite begomovirus squash leaf curl China virus (SLCCNV). We identified 2275 differentially-expressed genes (DEGs), of which 1310 were upregulated and 965 were downregulated. KEGG enrichment analysis of the DEGs revealed that many pathways related to primary and secondary metabolisms were enriched. qRT-PCR verified the transcriptional changes of twelve selected DEGs induced by SLCCNV infection. Close examination revealed that the expression levels of all the DEGs of the pathway Photosynthesis were downregulated upon SLCCNV infection. Most DEGs in the pathway Plant-pathogen interaction were upregulated, including some positive regulators of plant defenses. Moreover, the majority of DEGs in the MAPK signaling pathway-plant were upregulated.ConclusionOur findings indicates that SLCCNV actively interact with its cucurbitaceous plant host by suppressing the conversion of light energy to chemical energy and inducing immune responses. Our study not only provides new insights into the interactions between begomoviruses and host plants, but also adds to our knowledge on virus-plant interactions in general.

Squash leaf curl China virus (SLCCNV) belongs to the species Begomovirus cucurbitachinaense in the genus Begomovirus and can infect some Cucurbitaceae crops except for watermelon (Citrullus lanatus). In this study, watermelon plants showing symptoms typical to begomovirus infection in field were observed in Zhejiang Province of China, and SLCCNV presence was identified through PCR and next-generation sequencing (NGS). The pairwise sequence identity of the DNA-A genome shows that SLCCNV watermelon isolate belongs to the SLCCNV/CN strain and shares 96% nucleotide identity with the previously sequenced SLCCNV/CN. An infectious clone of SLCCNV watermelon isolate was constructed using the tandem repeat fragment method. Through agrobacterium-mediated inoculation, the clone could induce systemic infection with typical symptoms in watermelon, melon (Cucumis melo), squash (Cucurbita pepo), pumpkin (Cucurbita maxima), wax gourd (Benicasa hispida), cucumber (Cucumis sativus), and N. benthamiana. It was further demonstrated that the progeny virions derived from the cloned watermelon isolate could be transmitted by whitefly rather than the sap. To the best of our knowledge, this is the first report of a natural infection of SLCCNV on watermelon in China, and the first complete report on the molecular characteristics and pathogenicity of watermelon-infecting SLCCNV in the world.

Squash leaf curl China virus (SLCCNV) is a species in the genus Begomovirus that possess a bipartite genome. It is transmitted by the whitefly species Bemisia tabaci and infects cucurbit crops in various parts of the Old World (Wu et al., 2020). In 2020, tomato plants with curled, distorted and yellow leaves were found in a greenhouse in Shouguang, Shandong Province, China (Fig. S1). Leaves with these symptoms were collected from 11 plants and the total RNA was extracted with TRIzol reagent (Invitrogen, USA). Five RNA extracts of the highest quality were combined and a small RNA library was generated by the company (BGI-Shenzhen, China). About 22,338,920 clean reads (18-28nt) were acquired and assembled into larger contigs with the software Velvet 1.0.5. These were further compared against nucleotide sequences in the National Center for Biotechnology Information (NCBI) databases with BLASTn searches. Not unexpectedly, there were many assembled contigs that had high identities (90%-100% identities) with known tomato-infecting viruses, including 241 contigs matching tomato chlorosis virus, 26 contigs matching southern tomato virus, and 4 contigs matching tomato yellow leaf curl virus. However, 12 contigs had high identities (90%-100%) with the genomic DNA-A of SLCCNV, while 9 other contigs had high identities (90%-100%) with the genomic DNA-B of SLCCNV. To verify the presence of SLCCNV in tomato plants, two sets of primer pairs were designed according to the specific contigs assembled from derived small interfering RNAs (vsiRNAs). The primer pairs A742-F/A742-R (5'-GTAATACGAGCATCCGCACGGTAG-3'/5'-CGTGGAGGGCGAC AAACAGCTAACG-3') and B539-F/B539-R (5'-GCTACTTTCAAGGACGAAGAAGAGG-3'/5'-CG ACATAGATTTCTGGTCGGTGGGC-3') directed the amplification of 742 bp and 539 bp for DNA-A and DNA-B fragments, respectively, from the total genomic DNA of the 11 tomato samples. The DNA-A and DNA-B of SLCCNV were both detected from all of the tomato samples. After sequencing, the 742 bp PCR products shared 100% nucleotide sequence identity with the DNA-A of SLCCNV isolate GDXW (MW389919), whereas the PCR-amplified 539 bp fragments shared 100% nucleotide sequence identity with the DNA-B of SLCCNV isolate GDXW (MW389920). The full-length of DNA-A and DNA-B components were amplified with back-to-back primers A-F/A-R (Wu et al., 2020) and B-F/B-R (5'-GATAAACACGTCTCATTGCACCGC-3'/5'-GAGACGTGTTTATCAATATGGA CG-3'), respectively. The amplified fragments were further cloned into the PCE2TA/Blunt-Zero vector (Vazyme Biotech Co., China). After sequencing, the complete sequence of DNA-A was 2736 nt in length (MZ682117), while the DNA-B was 2718 nt in length (OK236348). The phylogenetic relationships of the DNA-A and DNA-B components were determined using MEGA 7 based on the full-length sequences of DNA-A and DNA-B, respectively (Kumar et al., 2016). Results showed that the DNA-A formed an independent cluster and was mostly related to the GDHY (MW389917) in the phylogenetic tree constructed using the neighbor-joining (NJ) method, while the DNA-B formed an independent cluster and was mostly related to the SLCCNV isolate BLDG (MW389928) and isolate GDBL (MW389922) (Fig. S2). The nt identities of DNA-A were also calculated with SDT v1.2 by comparison with other begomovirus sequences from the initial BLASTn analysis (Muhire et al., 2014), showing that the virus shared 99.4% sequence identity with SLCCNV isolate GDHY (MW389917). According to the current demarcation threshold for begomoviruses, recommended by the International Committee on Taxonomy of Viruses (ICTV) (91% nt identity) (Brown et al., 2015), this virus identified from tomato is a distinct strain of SLCCNV, designated SLCCNV-SDSG. To the best of our knowledge, this is the first report of a natural infection of SLCCNV on tomato in China. SLCCNV has caused serious problems in cucurbit production in some areas, so it will be important to investigate if tomato plays a role in the disease biology by serving as a reservoir host. The author(s) declare no conflict of interest. Funding: The funding for this research was supported by the Beijing Academy of Agriculture and Forestry Foundation, China (QNJJ202131, QNJJ201915, KJCX20200113).

Abstract. Temaja IGRM, Sudiarta IP, Wirya GNAS, Selangga DGW, Listihani L, Ambarawati IGAA, Kasim NN, Sapanca PLY, Pandawani NP. 2024. Begomovirus diversity and distribution on melon plants in Bali, Indonesia. Biodiversitas 25: 572-582. Melon crops in Bali, Indonesia often exhibit curling and yellowing symptoms in young plants, the cause of which remains unidentified. This research aimed to determine the presence of Begomovirus isolates from Bali and their distribution among melon plants. The research methods involved a comprehensive survey, meticulous sampling, precise virus detection with PCR, thorough sequencing analysis, and accurate calculation of viral disease incidence based on DNA sequencing results. Sampling and symptom observation were conducted in seven Bali regencies: Denpasar City, Gianyar, Badung, Tabanan, Buleleng, Jembrana, and Bangli. The PCR method with Begomovirus universal primers SPG1/SPG2 was used for virus identification, followed by nucleotide sequencing. The research identified three viruses infecting melon plants in Bali: Squash leaf curl virus (SLCuV), Squash leaf curl China virus (SLCCNV), and Squash leaf curl Philippines virus (SLCuPV). The highest disease incidence for SLCuV, SLCCNV, and SLCuPV was found in Denpasar, Buleleng, and Badung, at 40%, 30%, and 30%, respectively. SLCCNV has spread to seven regencies in Bali, namely Denpasar City, Gianyar, Tabanan, Buleleng, Bangli, and Jembrana. SLCuV has spread to six regencies in Bali, all except Badung Regency. SLCuPV was only found in Denpasar City, Badung, and Buleleng. The molecular characteristic of SLCuV Bali isolate has the closest nucleotide and amino acid homology with East Timor isolate (KY652743) which is 98.4% (99.0%), SLCCNV Bali isolate is closest with Malaysia isolate (EF197940) which is 98.8% (99.8%), and SLCuPV is closest with Taiwan isolate (JF746195) which was 98.8% (99.5%). The novelty of this research lies in the first report of SLCuPV infection in Curcubitaceae plants in Indonesia, a finding that could significantly impact our understanding of viral infections in crops.

Cucurbits are important economic crops worldwide. However, the cucurbit leaf curl disease (CuLCD), caused by whitefly-transmitted begomoviruses constrains their production. In Southeast Asia, three major begomoviruses, Tomato leaf curl New Delhi virus (ToLCNDV), Squash leaf curl China virus (SLCCNV) and Squash leaf curl Philippines virus (SLCuPV) are associated with CuLCD. SLCuPV and SLCCNV were identified in Luzon, the Philippines. Here, the genetic diversity and geographic distribution of CuLCD-associated begomoviruses in the Philippines were studied based on 103 begomovirus detected out of 249 cucurbit samples collected from 60 locations throughout the country in 2018 and 2019. The presence of SLCCNV and SLCuPV throughout the Philippines were confirmed by begomovirus PCR detection and viral DNA sequence analysis. SLCuPV was determined as a predominant CuLCD-associated begomovirus and grouped into two strains. Interestingly, SLCCNV was detected in pumpkin and bottle gourd without associated viral DNA-B and mixed-infected with SLCuPV. Furthermore, the pathogenicity of selected isolates of SLCCNV and SLCuPV was confirmed. The results provide virus genetic diversity associated with CuLCD for further disease management, especially in developing the disease-resistant cultivars in the Philippines as well as Southeast Asia.

A Begomovirus causing yellow vein mosaic disease of pumpkin (Cucurbita maxima L.) was characterized at molecular level by cloning and sequence analysis of its complete DNA‐A genome. The DNA‐A of the isolate contains 2758 nucleotides which encode six open reading frames (ORFs): AV1 and AV2 in the virion‐sense and AC1, AC2, AC3 and AC4 in the complementary‐sense. Based on the highest (96%) sequence identities and close phylogenetic relationships with Squash leaf curl China virus species, the Begomovirus was identified as strain of Squash leaf curl China virus. The presence of DNA‐B genome of the virus strain was also detected by dot blot hybridization test using DNA‐B specific probe.

Virus diseases are a major production constraint for pumpkin. Recessive resistance to squash leaf curl China virus and tomato leaf curl New Delhi virus has been mapped in Cucurbita moschata (Duchesne ex Poir.) breeding line AVPU1426 to chromosomes 7 and 8, respectively. Molecular markers tightly associated with the resistance loci have been developed and were able to correctly predict resistance and susceptibility with an accuracy of 99% for squash leaf curl China virus resistance and 94.34% for tomato leaf curl New Delhi virus in F2 and back cross populations derived from the original resistance source AVPU1426. The markers associated with resistance are recommended for use in marker-assisted breeding.

A bipartite begomovirus was identified from a Boehmeria leiophylla plant sample exhibiting yellow mosaic symptoms collected in Nabanhe National Nature Reserve, Xishuangbanna, Yunnan, China. Five complete DNA-A and four DNA-B genome sequences were obtained by rolling-circle amplification (RCA), cloned, and sequenced. All DNA-A sequences were determined to be 2759 nucleotides in size, sharing 99.9%-100% nucleotide sequence identity with each other. The DNA-B sequences were comprised of 2673 nucleotides, sharing 98.6-100% nucleotide sequence identity with each other. Genomic organization of the begomovirus was typical of Old World bipartite begomoviruses. Sequence analysis revealed 81.84% nucleotide sequence identity to tomato leaf curl Hsinchu virus (ToLCHsV) from China for the DNA A component and 67.23% identity to the squash leaf curl China virus (SLCCNV) from India for the DNA B component. The sequence comparisons suggest that this bipartite begomovirus represents a novel species for which we propose the name "Ramie yellow mosaic virus".

Chili pepper, tomato, and squash cultivated in Magelang Regency, Central Java Province, Indonesia showed severe viral symptoms. Three samples were taken then molecularly tested against begomovirus, potyvirus, tobamovirus, and polerovirus. However, PCR test confirmed only begomovirus infections. BLAST analysis concluded that the chili pepper and tomato isolates were pepper yellow leaf curl Indonesia virus (PepYLCIV) while the squash isolate was squash leaf curl China virus (SLCCNV). The 552 bp partial AV1 gene sequences of the three isolates were given NCBI GenBank acc nos. OR924278-80. PepYLCIV OR924279 and OR924280 formed a subgroup with LC542629 from Bali in the phylogenetic tree constructed using MEGA11, and shared 95.8 – 96.7% identities at nucleotide (nt) and 98.4 – 99.5% at amino acid (aa) levels according to Sequence Demarcation Tool v1.2 software. Meanwhile, SLCCNV OR924278 was clustered, and shared 95.8 – 96.7% nt and 98.4 – 99.5% aa identities with three Malaysian isolates (MW248685, MW248687, and MW248689). Different plant species inoculated with SLCCNV OR924278 remained symptomless up to four weeks observation, suggesting that the isolate is not mechanically transmissible. This study contributed additional knowledge on molecular variation while expanding hosts and distribution of PepYLCIV and SLCCNV in Central Java Province.

The biological and molecular properties of Squash leaf curl China virus from Varanasi, India (SLCCNV-IN[IN:Var:Pum]) were characterized. SLCCNV-IN[IN:Var:Pum] could be transmitted by grafting and through whitefly transmission. The complete DNA-A and DNA-B components were amplified through PCR using specific DNA-A and DNA-B primers. The DNA-A of the isolate was comprised of 2,738 nucleotides, encoding typical six open reading frames, and DNA-B of 2,704 nucleotides, encoding two ORFs. Genome organization of the isolate was typical of an old world bipartite begomovirus. Comparisons showed that DNA-A and its intergenic region have the highest sequence identity (97.6 and 97.4%, respectively) with the SLCCNV-IN[IN:Luc:Pum]; (DQ026296). This data suggested that the isolate is a same begomovirus species for which the name Squash leaf curl China virus-India[India:Varanasi:Pumpkin] is proposed. DNA-B showed maximum sequence identity (89.2%) with SLCCNV-IN[IN:Coi:Pum] (AY184488). Phylogenetic analysis of the present isolate showed close relationship to other cucurbit-infecting geminiviruses. This is the first evidence of occurrence of the bipartite Squash leaf curl China virus associated with severe yellow mosaic disease of pumpkin in northern India.

Molecular and biological characterization of melon-infecting squash leaf curl China virus in China

The genus Begomovirus from the family Geminiviridae is responsible for causing significant economic losses to many important horticultural crops, including cucumber (Cucumis sativus L.). Begomovirus infection during the early stages of plant growth can lead to complete yield loss. Hence, the identification of begomovirus species is important to design a precise resistant breeding strategy. This study aims to detect the presence of begomovirus in typical symptomatic cucumber leaves, identify the species of begomovirus present, and investigate the evolutionary relationships with other reported begomoviruses using phylogenetic analysis. Leaf samples from symptomatic cucumber plants were collected from the Green World Genetics (GWG) research station and a farm in Lembah Bidong, Rhu Tapai, Setiu, Terengganu. To detect the presence of begomovirus, PCR was carried out using universal primers targeting DNA-A, DNA-B, and betasatellite regions. DNA-A and betasatellite fragments were amplified, but not DNA-B. The amplified partial sequences of DNA-A were then analysed and compared with other begomovirus sequences in the GenBank database managed by the National Centre for Biotechnology Information (NCBI). The newly isolated DNA-A sequence from cucumber was 100% identical to the tomato leaf curl New Delhi virus (ToLCNDV). The phylogenetic tree was divided into two groups: group A, consisting of the newly isolated DNA-A sequence from cucumber, ToLCNDV, followed by squash leaf curl China virus (SLCCNV) and a monopartite begomovirus Ageratum yellow vein virus (AYVV); and group B, consisting of tomato yellow leaf curl Kanchanaburi virus (TYLCKaV), pepper yellow leaf curl Indonesia virus (PepYLCIV), and pepper yellow leaf curl Aceh virus (PepYLCAV). For the first time in cucumber, betasatellite is reported in association with ToLCNDV, a bipartite old-world begomovirus. This study provides a basis for the selection and breeding of begomovirus-resistant cucumber varieties in the future.

ABSTRACTWe present here the first complete Squash leaf curl China virus (SLCCV) genomic segment DNA-A sequence from East Timor. It was isolated from a pumpkin plant. When compared with 15 complete SLCCV DNA-A genome sequences from other world regions, it most resembled the Malaysian isolate MC1 sequence.