Search Results (36)

Begomoviruses infect many crops and weeds globally, especially in the tropical and subtropical regions, where there are waves of epidemics. These begomovirus epidemics are frequently associated with three DNA satellites: betasatellites, alphasatellites, and deltasatellites. Except for the origin of replication, these satellites show no sequence identity with the helper begomovirus. Alphasatellites and betasatellites encode the $\mathsf{\alpha }$-Rep and βC1 proteins, respectively, while deltasatellites encode no proteins. $\mathsf{\alpha }$-Rep, which functions like the Rep of the helper begomoviruses, ensures alphasatellite replication autonomy, while betasatellites and deltasatellites depend wholly on the helper virus for replication. The betasatellite βC1 protein is a pathogenicity determinant and suppressor of RNA silencing. The associations between satellites and helper viruses vary, depending on the virus and the host, and the roles of these satellites in disease development are an active area of investigation. This review highlights current information on the role of DNA satellites in begomovirus diseases and examines commonalities and differences between and within these satellites under prevailing conditions. Furthermore, two episomes, SEGS-1 and SEGS-2, associated with cassava mosaic geminiviruses, and their possible status as DNA satellites are discussed. DNA satellites are a major factor in begomovirus infections, which are a major constraint to crop production, especially in tropical and subtropical regions. Thus, areas for future research efforts, as well as implications in the biotechnological management of these viruses, are discussed in this review. Full article

Lettuce (Lactuca sativa L.) plants showing leaf curl and vein enation symptoms were found in Yunnan province, China. PCR detection with genus-specific primers revealed that symptomatic lettuce plants were infected with Begomovirus. The full-length viral component and satellite molecules were obtained by RCA, restriction enzyme digestion, PCR, cloning and DNA sequencing. A viral component (YN-2023-WJ) and three satellite molecules (YN-2023-WJ-alpha1, YN-2023-WJ-alpha2 and YN-2023-WJ-beta) were obtained from diseased lettuce plants. YN-2023-WJ exhibited the highest nt identity at 97.1% with pepper leaf curl Yunnan virus isolated from cigar plants. YN-2023-WJ-beta displayed the highest nt identity at 93.9% with tomato leaf curl China betasatellite. YN-2023-WJ-alpha1 showed the highest nt identity at 94.7% with ageratum yellow vein alphasatellite. YN-2023-WJ-alpha2 shared the highest nt identity at 75.6% with gossypium mustelinum symptomless alphasatellite and vernonia yellow vein Fujian alphasatellite. Based on the threshold for the classification of Begomovirus, Betasatellite and Alphasatellite, YN-2023-WJ was designated as a new isolate of PepLCYnV, YN-2023-WJ-beta as a new isolate of ToLCCNB and YN-2023-WJ-alpha1 as a new member of AYVA, whereas YN-2023-WJ-alpha2 was identified as a new geminialphasatellite species, for which the name pepper leaf curl Yunnan alphasatellite (PepLCYnA) is proposed. To the best of our knowledge, this is the first report of L. sativa L. infection by PepLCYnV associated with ToLCCNB, AYVA and PepLCYnA, and L. sativa L. is a new host plant of Begomovirus. Full article

Begomoviruses, transmitted by the whitefly Bemisia tabaci, pose significant threats to global agriculture due to their severe impact on various crops. Among the satellite molecules associated with begomoviruses, betasatellites play a crucial role in enhancing disease severity and yield losses. The spread and association of these molecules with helper viruses in host plants are thus matters of concern. Here, we focus on the propagation of betasatellites and, more specifically, on their transfer between different helper viruses and hosts through vector transmission. Our results show that the cotton leaf curl Gezira betasatellite (CLCuGeB), initially acquired with its helper virus cotton leaf curl Gezira virus (CLCuGeV) from an okra plant, can be transmitted and assisted by a different helper virus, tomato yellow leaf curl virus (TYLCV), in a different host plant (tomato plant). The new association can be formed whether TYLCV and CLCuGeB encounter each other in a host plant previously infected with TYLCV or in whiteflies having acquired the different components separately. Our findings reveal two pathways by which betasatellites can be transferred between helper viruses and host plants and highlight the ability of betasatellites to spread in begomovirus-infected environments. Full article

Begomoviruses have emerged as destructive pathogens of crops, particularly in the tropics and subtropics, causing enormous economic losses and threatening food security. Epidemics caused by begomoviruses have even spread in regions and crops that were previously free from these viruses. The most seriously affected crops include cassava; cotton; grain legumes; and cucurbitaceous, malvaceous, and solanaceous vegetables. Alphasatellites, betasatellites, and deltasatellites are associated with the diseases caused by begomoviruses, but begomovirus–betasatellite complexes have played significant roles in the evolution of begomoviruses, causing widespread epidemics in many economically important crops throughout the world. This article provides an overview of the evolution, distribution, and approaches used by betasatellites in the suppression of host plant defense responses and increasing disease severity. Full article

Alternanthera yellow vein virus (AlYVV), a monopartite begomovirus, has been identified infecting a diverse range of crops and native plants in Pakistan, India, and China. However, distinctive yellow vein symptoms, characteristic of begomovirus infection, were observed on the Ageratum conyzoides weed in Oman, prompting a thorough genomic characterization in this study. The results unveiled a complete genome sequence of 2745 base pairs and an associated betasatellite spanning 1345 base pairs. In addition, Sequence Demarcation Tool analyses indicated the highest nucleotide identity of 92.8% with a previously reported AlYVV-[IN_abalpur_A_17:LC316182] strain, whereas the betasatellite exhibited a 99.8% nucleotide identity with isolates of tomato leaf curl betasatellite. Thus, our findings propose a novel AlYVV Oman virus (AlYVV-OM) variant, emphasizing the need for additional epidemiological surveillance to understand its prevalence and significance in Oman and the broader region. To effectively manage the spread of AlYVV-OM and minimize its potential harm to (agro)ecosystems, future research should focus on elucidating the genetic diversity of AlYVV-OM and its interactions with other begomoviruses. Full article

Pepper plants (Capsicum annuum) with severe leaf curl symptoms were collected in 2013 from Bangalore, Karnataka, India. The detection results showed a co-infection between the tomato leaf curl Joydebpur virus (ToLCJoV) and tomato leaf curl Bangladesh betasatellite (ToLCBDB) through the sequencing analysis of PCR amplicons. To pinpoint the molecular mechanism of this uncommon combination, infectious clones of ToLCJoV and two different betasatellites—ToLCBDB and tomato leaf curl Joydebpur betasatellite (ToLCJoB)—were constructed and tested for their infectivity in Nicotiana benthamiana. Together, we conducted various combined agroinoculation studies to compare the interaction of ToLCJoV with non-cognate and cognate betasatellites. The natural non-cognate interaction between ToLCJoV and ToLCBDB showed severe symptoms compared to the mild symptoms of a cognate combination (ToLCJoV × ToLCJoB) in infected plants. A sequence comparison among betasatellites and their helper virus wasperformed and the iteron resemblances in ToLCBDB as well as ToLCJoB clones were processed. Mutant betasatellites that comprised iteron modifications revealed that changes in iteron sequences could disturb the transreplication process between betasatellites and their helper virus. Our study might provide an important consideration for determining the efficiency of transreplication activity between betasatellites and their helper virus. Full article

Salicylic acid (SA), benzothiadiazole (BTH), and methyl jasmonate (MeJA) are potential elicitors found in plants, playing a crucial role against various biotic and abiotic stresses. The systemic acquired resistance (SAR) mechanism was evaluated in cotton plants for the suppression of Cotton leaf curl Multan Virus (CLCuMuV) by the exogenous application of different elicitors. Seven different treatments of SA, MeJA, and BTH were applied exogenously at different concentrations and combinations. In response to elicitors treatment, enzymatic activities such as SOD, POD, CAT, PPO, PAL, β–1,3 glucanse, and chitinase as biochemical markers for resistance were determined from virus-inoculated and uninoculated cotton plants of susceptible and tolerant varieties, respectively. CLCuMuV was inoculated on cotton plants by whitefly (Bemesia tabaci biotype Asia II-1) and detected by PCR using specific primers for the coat protein region and the Cotton leaf curl betasatellite (CLCuMuBV)-associated component of CLCuMuV. The development of disease symptoms was observed and recorded on treated and control plants. The results revealed that BTH applied at a concentration of 1.1 mM appeared to be the most effective treatment for suppressing CLCuMuV disease in both varieties. The enzymatic activities in both varieties were not significantly different, and the disease was almost equally suppressed in BTH-treated cotton plants following virus inoculation. The beta satellite and coat protein regions of CLCuMuV were not detected by PCR in the cotton plants treated with BTH at either concentration. Among all elicitors, 1.1 mM BTH was proven to be the best option for inducing resistance after the onset of CLCuMuV infection and hence it could be part of the integrated disease management program against Cotton leaf curl virus. Full article

Cotton leaf curl disease (CLCuD) is a significant constraint to the economies of Pakistan and India. The disease is caused by different begomoviruses (genus Begomovirus, family Geminiviridae) in association with a disease-specific betasatellite. However, another satellite-like molecule, alphasatellite, is occasionally found associated with this disease complex. A quantitative real-time PCR assay for the virus/satellite components causing CLCuD was used to investigate the performance of selected cotton varieties in the 2014–2015 National Coordinated Varietal Trials (NCVT) in Pakistan. The DNA levels of virus and satellites in cotton plants were determined for five cotton varieties across three geographic locations and compared with seed cotton yield (SCY) as a measure of the plant performance. The highest virus titer was detected in B-10 (0.972 ng·µg⁻¹) from Vehari and the lowest in B-3 (0.006 ng·µg⁻¹) from Faisalabad. Likewise, the highest alphasatellite titer was found in B-1 (0.055 ng·µg⁻¹) from Vehari and the lowest in B-1 and B-2 (0.001 ng·µg⁻¹) from Faisalabad. The highest betasatellite titer was found in B-23 (1.156 ng·µg⁻¹) from Faisalabad and the lowest in B-12 (0.072 ng·µg⁻¹) from Multan. Virus/satellite DNA levels, symptoms, and SCY were found to be highly variable between the varieties and between the locations. Nevertheless, statistical analysis of the results suggested that betasatellite DNA levels, rather than virus or alphasatellite DNA levels, were the important variable in plant performance, having an inverse relationship with SCY (−0.447). This quantitative assay will be useful in breeding programs for development of virus resistant plants and varietal trials, such as the NCVT, to select suitable varieties of cotton with mild (preferably no) symptoms and low (preferably no) virus/satellite. At present, no such molecular techniques are used in resistance breeding programs or varietal trials in Pakistan. Full article

The molecular characterization of a tomato leaf curl New Delhi virus (ToLCNDV) isolate, denoted ToLCNDV-Le, is reported. The virus was associated with severe and recurrent outbreaks in protected crops of zucchini squash grown in the Province of Lecce (Apulia, southern Italy). The fully sequenced genome of ToLCNDV-Le consists of two genomic components named DNA-A and DNA-B of 2738 and 2683 nt in size, respectively. Like other ToLCNDV isolates, ToLCNDV-Le DNA-A contains the AV2 and AV1 open reading frames (ORFs) in the virion-sense orientation and five additional ORFs named AC1, AC2, AC3, AC4 and AC5 in the complementary-sense orientation. The DNA-B contains BV1 ORF in the virion-sense orientation and BC1 ORF in the complementary-sense orientation. No DNA betasatellites were found associated with ToLCNDV-Le in naturally infected samples. Phylogenetic analysis clustered ToLCNDV-Le with the ToLCNDV-ES strain of western Mediterranean Basin isolates. Consequently, the ToLCNDV-ES-[IT-Zu-Le18] name is proposed as the descriptor for ToLCNDV-Le. Using recombination detection program RDP4, one putative recombination breakpoint (Rbp) was identified close to nucleotide positions 2197–2727, covering approximately half of the AC1 region, including the AC4 ORF and the 3′ UTR. RDP4 indicated the event represents an Rbp of an isolate similar to ToLCNDV [Pk-06] (Acc. No. EF620534) found in Luffa acutangula in Pakistan and identified as putative minor parent into the background of ToLCNDV [BG-Jes-Svr-05] (Acc. No. AJ875157), found in tomato in Bangladesh, and identified as putative major parent. To the best of our knowledge, this is the first report of a ToLCNDV-ES recombinant isolate in the AC1-AC4 region in Italy. Full article

The Begomovirus genus of the family Geminiviridae comprises the largest group of geminiviruses. Begomoviruses are transmitted by the whitefly complex (Bemisia tabaci) and infect dicotyledonous plants in tropical and subtropical regions. The list of begomoviruses is continuously increasing as a result of improvements in the methods for identification, especially from weed plants, which are considered a source of new viruses and reservoirs of economically important viruses but are often neglected during diversity studies. Lathyrus aphaca L. weed plants (yellow-flowered pea) with varicose veins and discoloration of the leaves were found. Amplified genomic DNA through rolling circular amplification was subjected to PCR analysis for the detection of the viral genome and associated DNA-satellites (alphasatellites and betasatellites). A full-length sequence (2.8 kb) of a monopartite begomovirus clone was determined; however, we could not find any associated DNA satellites. The amplified full-length clone of Rose leaf curl virus (RoLCuV) reserved all the characteristics and features of an Old World (OW) monopartite begomovirus. Furthermore, it is the first time it has been reported from a new weed host, yellow-flowered pea. Rolling circle amplification and polymerase chain reaction analysis of associated DNA satellites, alphasatellite, and betasatellite, were frequently accomplished but unable to amplify from the begomovirus-infected samples, indicating the presence of only monopartite Old World begomovirus. It is observed that RoLCuV has the capability to infect different hosts individually without the assistance of any DNA satellite component. Recombination in viruses is also a source of begomovirus infection in different hosts. Full article

The begomovirus–betasatellite complex constantly threatens crops in Asia. However, the quantitative relationship between begomoviruses and betasatellites remains largely unknown. The quantities of tobacco curly shoot virus (TbCSV) and its betasatellite (TbCSB) and their ratio varied significantly in initial infection, and thereafter, the ratio tended to become constant. The TbCSB/TbCSV ratio in agrobacteria inoculum significantly affected that in plants in the initial infection but not thereafter. Null-mutation of βC1 that encodes a multifunctional protein important for pathogenesis in TbCSB significantly reduced the TbCSB/TbCSV ratio in plants. Viral inoculum plants with higher TbCSB/TbCSV ratios promoted whitefly transmission of the virus. The expression of AV1 encoded by TbCSV, βC1 encoded by TbCSB and the βC1/AV1 ratio varied significantly in the initial infection and thereafter the ratio tended to become constant. Additionally, the temporal dynamics of the ratio between another begomovirus and its betasatellite was similar to that of TbCSV and was positively regulated by βC1. These results indicate that the ratio between monopartite begomoviruses and betasatellites tend to become constant as infection progresses, and is modulated by βC1, but a higher betasatellite/begomovirus ratio in virally inoculated plants promotes virus transmission by whiteflies. Our findings provide novel insights into the association between begomoviruses and betasatellites. Full article

Arthropod-borne pathogens and parasites are major threats to human health and global agriculture. They may directly or indirectly manipulate behaviors of arthropod vector for rapid transmission between hosts. The largest genus of plant viruses, Begomovirus, is transmitted exclusively by whitefly (Bemisia tabaci), a complex of at least 34 morphologically indistinguishable species. We have previously shown that plants infected with the tomato yellowleaf curl China virus (TYLCCNV) and its associated betasatellite (TYLCCNB) attract their whitefly vectors by subverting plant MYC2-regulated terpenoid biosynthesis, therefore forming an indirect mutualism between virus and vector via plant. However, the evolutionary mechanism of interactions between begomoviruses and their whitefly vectors is still poorly understood. Here we present evidence to suggest that indirect mutualism may happen over a millennium ago and at present extensively prevails. Detailed bioinformatics and functional analysis identified the serine-33 as an evolutionary conserved phosphorylation site in 105 of 119 Betasatellite species-encoded βC1 proteins, which are responsible for suppressing plant terpenoid-based defense by interfering with MYC2 dimerization and are essential to promote whitefly performance. The substitution of serine-33 of βC1 proteins with either aspartate (phosphorylation mimic mutants) or cysteine, the amino acid in the non-functional sβC1 encoded by Siegesbeckia yellow vein betasatellite SiYVB) impaired the ability of βC1 functions on suppression of MYC2 dimerization, whitefly attraction and fitness. Moreover the gain of function mutation of cysteine-31 to serine in sβC1 protein of SiYVB restored these functions of βC1 protein. Thus, the dynamic phosphorylation of serine-33 in βC1 proteins helps the virus to evade host defense against insect vectors with an evolutionarily conserved manner. Our data provide a mechanistic explanation of how arboviruses evolutionarily modulate host defenses for rapid transmission. Full article

The studies on the prevalence and genetic diversity of begomoviruses in Saudi Arabia are minimal. In this study, field-grown symptomatic tomato and muskmelon plants were collected, and initially, begomovirus infection was confirmed by the core coat protein sequences. Four tomato and two muskmelon plants with viral infections were further evaluated for Illumina MiSeq sequencing, and twelve sequences (2.7–2.8 kb) equivalent to the full-length DNA-A or DNA-B components of begomoviruses were obtained along with eight sequences (~1.3–1.4 kb) equivalent to the begomovirus-associated DNA-satellite components. Four begomovirus sequences obtained from tomato plants were variants of tomato yellow leaf curl virus (TYLCV) with nt sequence identities of 95.3–100%. Additionally, two tomato plants showed a mixed infection of TYLCV and cotton leaf curl Gezira virus (CLCuGeV), okra yellow crinkle Cameroon alphasatellite (OYCrCMA), and okra leaf curl Oman betasatellite (OLCuOMB). Meanwhile, from muskmelon plants, two sequences were closely related (99–99.6%) to the tomato leaf curl Palampur virus (ToLCPalV) DNA-A, whereas two other sequences showed 97.9–100% sequence identities to DNA-B of ToLCPalV, respectively. Complete genome sequences of CLCuGeV and associated DNA-satellites were also obtained from these muskmelon plants. The nt sequence identities of the CLCuGeV, OYCrCMA, and OLCuOMB isolates obtained were 98.3–100%, 99.5–100%, and 95.6–99.7% with their respective available variants. The recombination was only detected in TYLCV and OLCuOMB isolates. To our knowledge, this is the first identification of a mixed infection of bipartite and monopartite begomoviruses associated with DNA-satellites from tomato and muskmelon in Saudi Arabia. The begomovirus variants reported in this study were clustered with Iranian isolates of respective begomovirus components in the phylogenetic dendrogram. Thus, the Iranian agroecological route can be a possible introduction of these begomoviruses and/or their associated DNA-satellites into Saudi Arabia. Full article

The selection of resistant crops is an effective method for controlling geminivirus diseases. ty-5 encodes a messenger RNA surveillance factor Pelota with a single amino acid mutation (Pelota^V16G), which confers effective resistance to tomato yellow leaf curl virus (TYLCV). No studies have investigated whether ty-5 confers resistance to other geminiviruses. Here, we demonstrate that the tomato ty-5 line exhibits effective resistance to various geminiviruses. It confers resistance to two representative begomoviruses, tomato yellow leaf curl China virus/tomato yellow leaf curl China betasatellite complex and tomato leaf curl Yunnan virus. The ty-5 line also exhibits partial resistance to a curtovirus beet curly top virus. Importantly, ty-5 confers resistance to TYLCV with a betasatellite. Southern blotting and quantitative polymerase chain reaction analyses showed that significantly less DNA of these geminiviruses accumulated in the ty-5 line than in the susceptible line. Moreover, knockdown of Pelota expression converted a Nicotiana benthamiana plant from a geminivirus-susceptible host to a geminivirus-resistant host. Overall, our findings suggest that ty-5 is an important resistance gene resource for crop breeding to control geminiviruses. Full article

Chilli leaf curl virus (ChiLCV), (Genus Begomovirus, family Geminiviridae) and associated satellites pose a serious threat to chilli production, worldwide. This study highlights the factors accountable for genetic diversity, recombination, and evolution of ChiLCV, and associated chilli leaf curl alphasatellite (ChiLCA) and chilli leaf curl betasatellite (ChiLCB). Phylogenetic analysis of complete genome (DNA-A) sequences of 132 ChiLCV isolates from five countries downloaded from NCBI database clustered into three major clades and showed high population diversity. The dN/dS ratio and Tajima D value of all viral DNA-A and associated betasatellite showed selective control on evolutionary relationships. Negative values of neutrality tests indicated purified selection and an excess of low-frequency polymorphism. Nucleotide diversity (π) for C4 and Rep genes was higher than other genes of ChiLCV with an average value of π = 18.37 × 10⁻² and π = 17.52 × 10⁻² respectively. A high number of mutations were detected in TrAP and Rep genes, while ChiLCB has a greater number of mutations than ChiLCA. In addition, significant recombination breakpoints were detected in all regions of ChiLCV genome, ChiLCB and, ChiLCA. Our findings indicate that ChiLCV has the potential for rapid evolution and adaptation to a range of geographic conditions and could be adopted to infect a wide range of crops, including diverse chilli cultivars. Full article