Optimization of DAC-ELISA and IC-RT-PCR using the developed polyclonal antibody and one-step RT-PCR assays for detection of Indian citrus ringspot virus in kinnow orange of Punjab, India.

Indian citrus ringspot virus (ICRSV), a member of the Mandarivirus genus, causes citrus ringspot disease, impacting kinnow orange quality and yield. Early and accurate detection methods are crucial before visible symptoms manifest in plants. In this study, a 507 bp partial coat protein gene (pCPG) segment was amplified from infected kinnow leaf tissues, cloned into a pET28a vector, and transformed into E. coli BL21(DE3) cells. Induced with IPTG, the cells overexpressed a recombinant partial coat protein (rpCP) of approximately 23 kDa, purified using Ni-NTA resin via affinity chromatography. Validated in western blot with an anti-His antibody, rpCP was used to generate an ICRSV-specific polyclonal antibody (PAb) in rabbits. PAb, optimized at 1:1000 dilution, successfully detected ICRSV in infected kinnow orange leaf extracts via DAC-ELISA and IC-RT-PCR assays. ICRSV was detectable in sample dilutions up to 1:640 and 1:10240 (w/v, g mL-1) by DAC-ELISA and IC-RT-PCR, respectively. One-step RT-PCR assays were also optimized, confirming the presence of ICRSV by amplifying a 507 bp pCPG fragment from total RNA extracted from kinnow orange leaves, with dilution up to 1:5120 (w/v, g mL-1). The result demonstrated that IC-RT-PCR has a 16-fold and 2-fold higher sensitivity than DAC-ELISA and one-step RT-PCR assays.

Candidatus Liberibacter asiaticus manipulates the expression of vitellogenin, cytoskeleton, and endocytotic pathway-related genes to become circulative in its vector, Diaphorina citri (Hemiptera: Psyllidae).

Citrus greening disease or huanglongbing (HLB) caused by Candidatus Liberibacter asiaticus (CLas) limits citrus production worldwide. CLas is transmitted by the Asian citrus psyllid (ACP), Diaphorina citri (Hemiptera: Psyllidae) in a persistent-propagative manner. Understanding the molecular interaction between CLas and ACP and interrupting the interrelationship can provide an alternative to insecticides for managing citrus greening disease. Transcriptome analysis of ACP in response to CLas showed differential expression of 3911 genes (2196 upregulated, and 1715 downregulated) including the key genes of ACP involved in cytoskeleton synthesis and nutrition-related proteins, such as vitellogenins, extensin, laminin, tropomyosin, troponin C, and flightin. Majority of the differentially expressed genes were categorized under molecular functions followed by cellular components and biological processes. KEGG pathway analysis showed differential regulation of carbohydrate, nucleotide, and energy metabolic pathways, the endocytotic pathway, and the defense-related pathways. Differential regulation of genes associated with the key pathways might favour CLas to become systemic and propagate in its insect vector. The study provides an understanding of genes involved in circulation of CLas in ACP. The candidate genes involved in key physiological processes and CLas transmission by ACP would be potential targets for sustainable management of ACP and CLas. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13205-021-02641-x.

The role of enzymatic activities of antiviral proteins from plants for action against plant pathogens.

Antiviral proteins (AVPs) from plants possess multiple activities, such as N-glycosidase, RNase, DNase enzymatic activity, and induce pathogenesis-related proteins, salicylic acid, superoxide dismutase, peroxidase, and catalase. The N-glycosidase activity releases the adenine residues from sarcin/ricin (S/R) loop of large subunit of ribosomes and interfere the host protein synthesis process and this activity has been attributed for antiviral activity in plant. It has been shown that AVP binds directly to viral genome-linked protein of plant viruses and interfere with protein synthesis of virus. AVPs also possess the RNase and DNase like activity and may be targeting nucleic acid of viruses directly. Recently, the antifungal, antibacterial, and antiinsect properties of AVPs have also been demonstrated. Gene encoding for AVPs has been used for the development of transgenic resistant crops to a broad range of plant pathogens and insect pests. However, the cytotoxicity has been observed in transgenic crops using AVP gene in some cases which can be a limiting factor for its application in agriculture. In this review, we have reviewed various aspects of AVPs particularly their characteristics, possible mode of action and application.

Production of mono- and polyclonal antibodies to Citrus leprosis virus C2 and their application in triple antibody sandwich ELISA and immunocapture RT-PCR diagnostic assays.

The newly discovered Citrus leprosis virus cytoplasmic type 2 (CiLV-C2) is one of the causal virus of citrus leprosis disease complex; which leads to substantial loss of citrus production in the states of Meta and Casanare of Colombia. Specific and sensitive detection methods are needed to monitor the dissemination of CiLV-C2 in Colombia, and to prevent introduction of CiLV-C2 to other citrus growing countries. Toward this end, putative coat protein gene (CPG) of CiLV-C2 was amplified from CiLV-C2 infected citrus tissues. The CPG was cloned, expressed and purified a recombinant coat protein of ∼31kDa which used to generate monoclonal antibodies and polyclonal antisera. Four monoclonal antibodies and two polyclonal antisera were selected as being specific following Western blotting. The monoclonal antibody MAb E5 and polyclonal antiserum PAb UF715 were selected testing with an extract of CiLV-C2 infected leaves using triple antibody sandwich enzyme-linked immunosorbent assay (TAS-ELISA). In addition, an immunocapture RT-PCR was standardized using MAb E5 for specific and sensitive detection of CiLV-C2. The standardized TAS-ELISA and IC-RT-PCR were able to detect CiLV-C2 in the extracts of symptomatic citrus leprosis tissues up to the dilutions of 1:160 and 1:2580, respectively. Result demonstrated that CiLV-C2 is present in citrus orchards in Meta and Casanare citrus growing areas of Colombia. TAS-ELISA could be used for routine detection of CiLV-C2, epidemiological studies, and for border inspections for quarantine purposes. IC-RT-PCR could be valuable for CiLV-C2 validation and viral genome analysis.

Detection of Citrus leprosis virus C using specific primers and TaqMan probe in one-step real-time reverse-transcription polymerase chain reaction assays.

Citrus leprosis virus C (CiLV-C), a causal agent of the leprosis disease in citrus, is mostly present in the South and Central America and spreading toward the North America. To enable better diagnosis and inhibit the further spread of this re-emerging virus a quantitative (q) real-time reverse transcription polymerase chain reaction (qRT-PCR) assay is needed for early detection of CiLV-C when the virus is present in low titer in citrus leprosis samples. Using the genomic sequence of CiLV-C, specific primers and probe were designed and synthesized to amplify a 73 nt amplicon from the movement protein (MP) gene. A standard curve of the 73 nt amplicon MP gene was developed using known 10(10)-10(1) copies of in vitro synthesized RNA transcript to estimate the copy number of RNA transcript in the citrus leprosis samples. The one-step qRT-PCR detection assays for CiLV-C were determined to be 1000 times more sensitive when compared to the one-step conventional reverse transcription polymerase chain reaction (RT-PCR) CiLV-C detection method. To evaluate the quality of the total RNA extracts, NADH dehydrogenase gene specific primers (nad5) and probe were included in reactions as an internal control. The one-step qRT-PCR specificity was successfully validated by testing for the presence of CiLV-C in the total RNA extracts of the citrus leprosis samples collected from Belize, Costa Rica, Mexico and Panama. Implementation of the one-step qRT-PCR assays for CiLV-C diagnosis should assist regulatory agencies in surveillance activities to monitor the distribution pattern of CiLV-C in countries where it is present and to prevent further dissemination into citrus growing countries where there is no report of CiLV-C presence.

Identification and Molecular Characterization of Nuclear Citrus leprosis virus, a Member of the Proposed Dichorhavirus Genus Infecting Multiple Citrus Species in Mexico.

Citrus leprosis is one of the most destructive diseases of Citrus spp. and is associated with two unrelated virus groups that produce particles primarily in either the cytoplasm or nucleus of infected plant cells. Symptoms of leprosis, including chlorotic spots surrounded by yellow haloes on leaves and necrotic spots on twigs and fruit, were observed on leprosis-affected mandarin and navel sweet orange trees in the state of Querétaro, Mexico. Serological and molecular assays showed that the cytoplasmic types of Citrus leprosis virus (CiLV-C) often associated with leprosis symptomatic tissues were absent. However, using transmission electron microscopy, bullet-shaped rhabdovirus-like virions were observed in the nuclei and cytoplasm of the citrus leprosis-infected leaf tissues. An analysis of small RNA populations from symptomatic tissue was carried out to determine the genome sequence of the rhabdovirus-like particles observed in the citrus leprosis samples. The complete genome sequence showed that the nuclear type of CiLV (CiLV-N) present in the samples consisted of two negative-sense RNAs: 6,268-nucleotide (nt)-long RNA1 and 5,847-nt-long RNA2, excluding the poly(A) tails. CiLV-N had a genome organization identical to that of Orchid fleck virus (OFV), with the exception of shorter 5' untranslated regions in RNA1 (53 versus 205 nt) and RNA2 (34 versus 182 nt). Phylogenetic trees constructed with the amino acid sequences of the nucleocapsid (N) and glycoproteins (G) and the RNA polymerase (L protein) showed that CiLV-N clusters with OFV. Furthermore, phylogenetic analyses of N protein established CiLV-N as a member of the proposed genus Dichorhavirus. Reverse-transcription polymerase chain reaction primers for the detection of CiLV-N were designed based on the sequence of the N gene and the assay was optimized and tested to detect the presence of CiLV-N in both diseased and symptom-free plants.

Production of monoclonal antibodies for detection of Citrus leprosis virus C in enzyme-linked immuno-assays and immunocapture reverse transcription-polymerase chain reaction.

Citrus leprosis virus C (CiLV-C) causes damage in citrus production in the South and Central America. Since closely related types of citrus viruses have recently been described monoclonal antibodies (MAbs) are needed for accurate and sensitive diagnosis of CiLV-C. In this study, MAbs to the expressed coat protein of CiLV-C were produced for serological detection of CiLV-C in crude extracts of infected tissues in double antibody sandwich enzyme-linked immunosorbent assays (DAS-ELISA), dot blot immunosorbent assays (DBIA) and immuonocapture-reverse transcription-polymerase chain reaction (IC-RT-PCR) procedures. Monoclonal antibodies were developed in mice to the purified expressed coat protein of CiLV-C. The published standard protocols of DAS-ELISA, DBIA and IC-RT-PCR were followed for the detection of coat protein p29 of CiLV-C in the crude extracts of CiLV-C infected tissues. Two monoclonal antibodies, designated G10 and C11, were identified from four potential candidates for the specific and sensitive detection of coat protein p29 of CiLV-C in the crude citrus extracts of CiLV-C infected tissues in DAS-ELISA, whereas G10 was also selected based on performance for use in the DBIA and IC-RT-PCR diagnostic assays. Sensitivity analysis comparing the three methods for detection of coat protein p29 of CiLV-C determined that IC-RT-PCR was more sensitive than DAS-ELISA and DBIA. The creation of MAbs to CiLV-C allows for the sensitive and accurate detection of the virus from CiLV-C infected citrus leaf tissues. Successful detection of the virus in three diagnostic assays formats provides flexibility to diagnosticians who can use either ELISA or DBIA for screening large numbers of samples, and IC-RT-PCR for rapid, sensitive confirmation testing.

Immunodiagnosis of Citrus leprosis virus C using a polyclonal antibody to an expressed putative coat protein.

Citrus leprosis virus C (CiLV-C), a causal agent for citrus leprosis disease, is present in South and Central America and is a threat for introduction into the U.S. citrus industry. A specific, inexpensive and reliable antibody based detection system is needed for the rapid identification of CiLV-C. The CiLV-C is very labile and has not been purified in sufficient amount for antibody production. The p29 gene of CiLV-C genome that codes for the putative coat protein (PCP) was codon optimized for expression in Escherichia coli and synthesized in vitro. The optimized gene was sub-cloned into the bacterial expression vector pDEST17 and transferred into E. coli BL21AI competent cells. The expression of PCP containing N-terminal His-tag was optimized by induction with l-arabinose. Induced cells were disrupted by sonication and expressed PCP was purified by affinity chromatography using Ni-NTA agarose. The purified expressed PCP was then used as an immunogen for injections into rabbits to produce polyclonal antibody (PAb). The PAb specific to the expressed PCP was identified using Western blotting. The antibody was successfully used to detect CiLV-C in the symptomatic CiLV-C infected tissues using double antibody sandwich-enzyme-linked-immunosorbent (DAS-ELISA), indirect ELISA and dot-blot immunoassay (DBIA) formats.

Genome assembly of citrus leprosis virus nuclear type reveals a close association with orchid fleck virus.

The complete genome of citrus leprosis virus nuclear type (CiLV-N) was identified by small RNA sequencing utilizing leprosis-affected citrus samples collected from the state of Querétaro, Mexico. The nucleotide identity and phylogenetic analysis indicate that CiLV-N is very closely related to orchid fleck virus, which typically infects Cymbidium species.

The Prevalence of the Citrus tristeza virus Trifoliate Resistance Breaking Genotype Among Puerto Rican Isolates.

Citrus tristeza virus (CTV) isolates have been grouped into six genotypes: T3, T30, T36, VT, B165, and resistance breaking (RB) based on symptoms, host range, and genomic sequence data. The RB genotype has recently been identified with the novel property of replicating in trifoliate orange trees, a resistant host for the other five genotypes. Puerto Rican CTV isolate B301 caused mild vein clearing symptoms in Mexican lime but did not induce seedling yellows or stem pitting reactions in appropriate indicator Citrus spp., which are typical host reactions of the isolate T30. The isolate B301 was not detected by the genotype specific primer (GSP), which identifies the CTV-T3, -T30, -T36, -VT, and B165 genotypes. A primer pair for reverse transcription polymerase chain reaction (RT-PCR) amplification of the CTV-RB genotype was designed from the heat shock protein (p65) region based on the complete genomic sequences of trifoliate RB isolates from New Zealand available in the GenBank databases. The amplicon sequence from isolate B301 was 98% identical to that of the other trifoliate RB isolates. In addition, B301 was successfully inoculated into 'Carrizo citrange' (a trifoliate hybrid) but did not induce any symptoms. Furthermore, the complete genome sequence of B301 followed by the phylogenetic analysis revealed that the isolate is part of the RB clade with other CTV-RB isolates from New Zealand and Hawaii. Additional CTV isolates obtained from Puerto Rico were tested with the RB-GSP and confirmed the presence of trifoliate RB isolates in mixed infection with known CTV genotypes. Although this is the first report of a CTV trifoliate RB genotype from Puerto Rico, this genotype was present there prior to 1992.

A novel virus of the genus Cilevirus causing symptoms similar to citrus leprosis.

Citrus leprosis in Colombia was previously shown to be caused by cytoplasmic Citrus leprosis virus (CiLV-C). In 2011, enzyme-linked immunosorbent assay and reverse-transcription polymerase chain reaction (RT-PCR)-based diagnostic methods failed to identify CiLV-C from citrus samples with symptoms similar to citrus leprosis; however, virions similar to CiLV-C were observed in the cytoplasm of the symptomatic leaves by transmission electron microscopy. Furthermore, the causal organism was transmitted by the false spider mite, Brevipalpus phoenicis, to healthy citrus seedlings. A library of small RNAs was constructed from symptomatic leaves and used as the template for Illumina high-throughput parallel sequencing. The complete genome sequence and structure of a new bipartite RNA virus was determined. RNA1 (8,717 nucleotides [nt]) contained two open reading frames (ORFs). ORF1 encoded the replication module, consisting of five domains: namely, methyltransferase (MTR), cysteine protease-like, FtsJ-MTR, helicase (Hel), and RNA-dependent RNA polymerase (RdRp); whereas ORF2 encoded the putative coat protein. RNA2 (4,989 nt) contained five ORFs that encode the movement protein (MP) and four hypothetical proteins (p7, p15, p24, and p61). The structure of this virus genome resembled that of CiLV-C except that it contained a long 3' untranslated terminal region and an extra ORF (p7) in RNA2. Both the RNA1 and RNA2 of the new virus had only 58 and 50% nucleotide identities, respectively, with known CiLV-C sequences and, thus, it appears to be a novel virus infecting citrus. Phylogenetic analyses of the MTR, Hel, RdRp, and MP domains also indicated that the new virus was closely related to CiLV-C. We suggest that the virus be called Citrus leprosis virus cytoplasmic type 2 (CiLV-C2) and it should be unambiguously classified as a definitive member of the genus Cilevirus. A pair of CiLV-C2 genome-specific RT-PCR primers was designed and validated to detect its presence in citrus leprosis samples collected from the Casanare and Meta states in Colombia.

Cloning and expression of antiviral/ribosome-inactivating protein from Bougainvillea xbuttiana.

A full-length cDNA encoding ribosome-inactivating/antiviral protein (RIP/AVP)from the leaves of Bougainvillea x buttiana was isolated. The cDNA consisted of 1364 nucleotides with an open reading frame (ORF)of 960 nucleotides encoding a 35.49 kDa protein of 319 amino acids. The deduced amino acid sequence has a putative active domain conserved in RIPs/AVPs and shows a varying phylogenetic relationship to the RIPs from other plant species. The deduced protein has been designated BBAP1 (Bougainvillea x buttiana antiviral protein1). The ORF was cloned into an expression vector and expressed in E.coli as a fusion protein of approximately 78 kDa. The cleaved and purified recombinant BBAP1 exhibited ribosome-inhibiting rRNA N-glycosidase activity,and imparted a high level of resistance against the tobacco mosaic virus (TMV).

Cloning and characterization of drought responsive partial gene sequence(s) from Oryza sativa L. subsp. Indica.

Differential display gels were run for the drought tolerant (N-22) and drought susceptible (Panidhan) genotypes of rice (Oryza sativa) to identify the genes showing differential expression with respect to moisture stress. Differential cDNA products were cloned in PCR-Trap vector and analyzed for differential expression by Northern hybridization. Two clones namely R4A and R7G were found to be associated with water deficit stress (WDS). Sequencing revealed an insert of 244 bp in the clone R4A. BLASTN and FASTA results showed that R4A had maximum homology with a full-length cDNA clone: 002-110-H10 and OSJNBa006109.12 protein. GO classification suggested that it had beta-glucosidase motif which had been implicated in ABA mobilization and thereby ABA dependent gene expression.