These are due to overgrowth or hyperplasia. The crown gall of beets and hairy root of apple are the examples. Fire blight of apple, and pear and soft rot of carrot and turnip are the common examples. The following Table 3 gives a list of some important disease-causing bacteria, host plants and diseases[1]. In the research of genetics virus used.
It is an important subject in genetic engineering. Harmful roles virus destroys plenty of bacteria useful for humans Different diseases like common Cold, Influenza, Mumps, Pox, Polio, Yellow fever, Harpish, Aids etc are caused by the attack of virus.
Viral Diseases in Animals Virus does not produce symptoms directly in the animals humans. But it indirectly affects the host. Some virus stimulates the lysosome of host cell to produce hydrolytic enzymes. These enzymes cause bursting of host cell. These hydrolytic enzymes damage other cells. Sometimes, envelope of the virus is toxic to the body of host. It causes allergic reactions.
It stimulates the genes of host cells. Thus host cell start dividing and produce tumor cancer. In some cases, virus destroy the immune system of the host like AIDS. T- Lymphocytes are major component of the immune system.
It results in failure of immune system. So the infected person is attacked by many diseases. The HIV also infects the cells of the central nervous system brain and spinal cord. Its symptoms are sudden weight loss, swollen lymph nodes and general loss of immunity. Cancer: Some retroviruses have special genes called oncogenes.
These viruses are called tumor viruses. These viruses inject these genes into host cells. Thus divisions start in the host cells. It produces tumor. The cell of this tumor may spread to other part of the body and cause cancer. Hepatitis: The inflammation of the liver is called hepatitis.
It is caused by viral infection. Its symptoms are: Jaundice, abdominal pain, Liver enlargement, Fatigue and sometimes fever. It may be mild. Sometimes it is acute and can cause liver cancer. Polio: Poliomyelitis is caused by polio virus. It is present all over the world. It occurs mostly in childhood. The polio virus is the smallest know virus.
It contains RNA in spherical capsid. Polio virus attack on nervous system. It makes the children handicapped. Influenza and cold: These are caused by influenza and cold virus. It is an enveloped RNA virus. Influenza and cold is a wide spread disease. It occurs in epidemic form.
Both these diseases infect the respiratory tract. Small pox: Small pox is caused by pox virus. It is a DNA enveloped virus. Small pox was common disease of the world before early twentieth century. Raised vesicles are formed on the body. These vesicles are fluid — filled. Later, these vesicles changes into pustules.
These pustules later forms pitted scars. After exposure, electron microscopy Wayadande and Fletcher, or immunofluorescence assays Labroussaa et al. Another very abundant membrane protein of S. This suggests that spiralin may mediate pathogen interactions within the insect vector, though specific mechanisms remain unknown.
As a taxon they have a wide host range, infecting more than different plant species Hogenhout et al. Collectively, more than plant diseases are caused by phytoplasmas that are transmitted by leafhoppers and, to a lesser extent, a few other hemipterans Mitchel, ; Weintraub and Beanland, ABC transporters shuttle metabolites across bacterial membranes, and are predicted to allow nutrient and metabolite uptake from the host.
This secretion system allows the delivery of functionally distinct proteins with a characteristic signal peptide at the n -terminal to the bacterial membrane. Because phytoplasmas have a single membrane, after the signal peptide is cleaved the proteins are released into the host environment secreted. Secreted phytoplasma proteins can alter host functions and act as effectors Bai et al. SAP effectors often alter host function by manipulating plant hormone homeostasis.
This leads to abnormal vegetative growth and increased fecundity for leafhopper vectors on infected plants Lu et al. SAP effectors can also modulate pathogenicity through changes in development.
A second group of proteins delivered by the Sec-secretion system are the immunodominant membrane proteins IMPs , which remain anchored and decorate the external membrane of phytoplasmas. IMPs are unique for phytoplasmas and are categorized into three subgroups depending on whether the n- or c- terminal side of the protein is exposed extracellularly Amp, IdpA, or Imp; Kakizawa et al.
The genus Liberibacter spp. These four species all depend on psyllid vectors for transmission and as alternative hosts Fagen et al. To date, only Liberibacter crescens has been cultured in vitro , but it is not considered phytopathogenic and it is not vector-borne Fagen et al.
Non-psyllid hemipterans may also be able to pick up the bacteria during feeding as bacterial DNA has been found in mealybugs Pitino et al. Similar to phytoplasmas, liberibacters lack biosynthesis genes for amino acids, sugars, and nitrogenated bases, which imply they obtain those metabolic products from their host Thompson et al.
Accordingly, many ABC transporters are encoded in liberibacter genomes Lin et al. Active importation of nutrients from phloem and insect vectors may lead to nutrient imbalances, partially explaining the foliar symptoms observed in liberibacter-infected plants Rashed et al. Potential pathogenicity mechanisms of liberibacters have recently been suggested based on comparative bioinformatics with other phloem-limited bacteria.
Liberibacters encode the basic proteins for Sec-dependent translocation, similar to phytoplasmas Lin et al. However, as liberibacters have two membranes of different composition in contrast to phytoplasmas, it is not known whether putative liberibacter Sec-transported proteins cross the outer membrane and interact with the plant or insect host. SA is an important signaling molecule involved in plant defense to pathogens and insects Glazebrook, ; Walling, ; Erb et al.
Recently, a NahG-like salicylate hydroxylase gene was found in the liberibacter genome. NahG is predicted to cleave salicylates derived from SA Lin et al. Although comparative bioinformatics has revealed many potential proteins used by liberibacter to alter plant and vector metabolism and vector—plants interactions, exact mechanisms for host colonization and transmission remain largely unknown.
The current understanding of pathogenicity mechanisms in vector-borne bacteria is largely influenced by the ability to culture those bacteria. To date only X. Because of this limitation, much of the biology and mechanisms of host colonization for phytoplasmas and liberibacters are still poorly understood Bove and Garnier, Another challenge of working with phloem-limited vector-borne bacteria in particular is the non-homogenous distribution in the phloem tissue.
This makes choosing sampling locations difficult and can result in false negatives during detection. Further, symptoms vary significantly across plant hosts and do not necessarily correlate with pathogen titer. Despite these difficulties, approaches combining genomics, bioinformatics, transcriptomics, and genetic manipulation have contributed to recent advances in the understanding of how these bacterial pathogens colonize their host environments.
This has allowed scientists to study bacterial gene function within these systems without the need to culture the organism. Bioinformatics can be used to compare genome sequences with the annotated genomes of close relatives or analyze sequences using server-based algorithms to assign predicted functions to each coding region Rutherford et al. Amino acid sequences can be further explored to identify conserved patterns and domains. In this way, proteins with low average similarity can be assigned to a predicted function Yu et al.
Finally, functions of unknown proteins can even be predicted using dedicated algorithms that identify patterns associated with signal peptides, localization, cleavage sites, phosphorylation, and transmembrane domains Yu et al. A limitation of these various bioinformatics approaches is that all programs are trained using cultured organisms. For unculturable bacteria, many unique sequences with no homologs in cultured species exist, making comparisons and inferences difficult Kube et al.
Despite these limitations, bioinformatics have been used successfully to study gene function for many phytoplasma effectors. Bai et al. In this study, they utilized a pipeline to predict prokaryotic signal peptides recognized by Sec-translocases SignalP v. After potential pathogenicity factors are identified, functional validation is required. For unculturable bacteria, transcription and translation of targets can only be evaluated within their hosts plant or insect.
This means RNA and protein isolations must be done from infected host tissue. By some estimates, only 0. Others report only 0. However, high throughput sequencing technologies have expanded the possibilities for studying pathogens inside their hosts. This technique has advantages over microarrays and qRT-PCR because it affords higher sensitivity for monitoring gene expression levels, independence from examining only known sequences, and wider detection ranges Westermann et al.
However, for vector-borne bacterial pathogens, RNAseq approaches have thus far had low levels of success. Prior to preparation for sequencing, total RNA was treated with a plant ribosomal depletion kit to enrich the samples for bacterial RNA. Only 0. Mapped reads corresponded to genes out of the predicted genes. In another RNAseq study, RNA was enriched for bacterial transcripts using a ribosomal depletion kit to remove plant cytoplasmic, mitochondrial, and chloroplast ribosomal RNA Abba et al.
Despite the enrichment and relatively deep sequencing, only 0. However, only 0. Transcriptomics offer a unique opportunity to overcome the many difficulties posed by these difficult pathosystems, but as evident in the above examples, many technical challenges remain. The first approach that permitted gene function discovery for vector-borne bacterial plant pathogens was the use of transposon mutagenesis with spiroplasmas in the early s Fletcher et al.
In this approach, a transposon with a selective marker was integrated randomly into the chromosome of S. When transformed colonies were tested in the host, the transposon was retained for a few days without antibiotic pressure.
This technique was used to determine that disruption of a solute binding protein gene sc76 reduced transmission in the leafhopper vector Boutareaud et al. Since this first study, numerous research groups have generated collections of S.
Currently, X. Genetic manipulation using surrogate culturable bacteria and heterologous gene expression in plants has been used to test gene function for other vector-borne bacteria Jain et al.
In a study using the flavescence dore phytoplasma, the surface protein, variable membrane protein A VmpA , was expressed under the control of the S. The tuf promoter was chosen because the tuf gene is expressed at high levels in most bacteria Kim et al. In this system the leafhopper, Euscelidius variegatus , serves as a vector for both the phytoplasma and S. Thus gain of function studies could be conducted with the recombinant S. However, biological inferences from this system may be restricted by the lack of host infection of L.
An alternative method for studying gene function is to overexpress bacterial candidate proteins in the plant host. Model plants such as Arabidopsis thaliana and Nicotiana spp. Once the candidate gene is selected, the coding sequence is cloned into a suitable expression vector and transgenic plants can be generated. Several authors have utilized plant heterologous expression systems to investigate the function of phytoplasma SAPs MacLean et al.
In these studies transgenic A. A limitation of this approach is that only profound disturbances caused by a single bacterial gene can be identified. In addition, model plants may not serve as natural hosts for all vectored-borne bacteria and relevance of findings may be limited to an artificial system. Controlling vector-borne pathogens is difficult. Chemical control of insect vectors is the most widely used method, but in most cases insecticidal applications are not sufficient to contain the spread of these pathogens and associated diseases.
Furthermore, insect resistance and environmental regulations have limited the viability of long-term application of insecticides. Host plant resistance has been successful for several high value crops Bisognin et al.
In these plants, X. Due to the long time periods required to identify resistance and produce new varieties, this method may not always be a practical choice for the more aggressive and devastating outbreaks.
One recent approach to block transmission of vector-borne bacteria used chemicals intended to saturate the pathogen-binding site in the insect or on the bacteria surface, so the insect picks up fewer pathogen cells Killiny et al. In this study, vectors were fed artificial diet supplemented with X. Multiple lectins, carbohydrates, and antibodies were evaluated for potential transmission blocking characteristics. After feeding on the diet-bacteria mixture, insects were transferred to healthy plants to determine transmission efficiency with and without the different chemicals Killiny et al.
Diets containing certain lectins wheat germ agglutinin and concanavalin A , N -acetyl glucosamine carbohydrates, and certain antibodies reduced the transmission efficiency under greenhouse conditions.
The authors suggest that lectins probably compete with the bacteria for the binding sites inside the insect, while carbohydrate saturate X. The interference approach has also been explored in phytoplasmas using antibodies against the extracellular membrane protein Amp, with some success in the lab Rashidi et al. Recently, phage-display libraries have been used to evaluate antibodies and protein—protein interactions inside the insect vector. In this approach, each phage contains a known peptide and the binding capacity of the peptide to an extracellular bacterial epitope is evaluated Huang et al.
The exact mechanisms mediating the ability of specific chemicals to block transmission is still unknown, and it is not clear how this technology could be used in large-scale application. How, for example, might a natural population of insects be exposed to the transmission-blocking chemical? Selfish DNA is a naturally occurring phenomenon where certain genetic elements, such as transposable elements and others, spread in the genome of an organism and in the population by making additional copies of themselves.
It has been suggested that selfish genetic elements could be used for control as a gene drive system that carries additional genes with anti-pathogen effects Sinkins and Gould, ; Gantz and Jasinskiene, Obvious concerns with this method are public acceptance of transgenic organisms, non-target impacts, and the costs of implantation. RNAi has already been successfully exploited in plants to control viruses in commercial production Tricoll et al. RNAi can also be used to control insect species, altering insect reproduction, physiology, or survival Gordon and Waterhouse, ; Wuriyanghan et al.
Direct injection, bait feeding, or transgenic host plants can be used to induce RNAi in insects. As direct injection is not practical for large scale control, and bait feeding is not effective in field studies for hemipteran insects, transgenic plants are the best options for using RNAi to control vectors of bacterial pathogens. While there is much excitement about the use of RNAi as an alternative control strategy Gordon and Waterhouse, ; Donald et al. Despite these unknowns, RNAi studies still represent an excellent attempt at next-generation control for these important plant pathogens.
Whereas most plant-infecting viruses depend on hemipterans for transmission, most plant-infecting bacteria do not. This is in contrast to the non-propagative relationships most vector-borne plant viruses share with hemipteran vectors.
The ability to transition between divergent hosts is remarkable considering that most vector-borne bacteria have highly reduced genomes compared their free-living ancestors, yet, we still do not understand the mechanisms which make this sort of transitioning possible. However, conclusions based on tissue tropisms should be made with caution, as only one xylem-limited vector-borne species has been identified so far.
Clearly, the role of membrane-associated proteins and extracellular structures represents the first target for investigating physical recognition inside the vector and initiation of host processes. However, the methodological bias toward these functional categories may limit our understanding of other important mechanisms mediating interactions with hosts.
Considering the highly reduced genomes and host-dependence of these bacteria, genes without an assigned function likely still play a significant role in the biology of the organism and will need to be investigated. Despite these advances, research on vector-borne pathogens is still in its infancy. Some of the most significant gaps in our understanding concern interactions with insect vectors. In particular, our understanding of leafhopper and psyllid feeding behavior, immunity, and plant responses to these insects needs to be improved.
Genetic resources for these important vectors also need to be expanded. Promisingly, the genomes for the psyllid Diaphorina citri 1 and at least one planthopper have been sequenced Noda et al. However, accessibility and quality control of insect genomic data remains an ongoing concern for the entomological community. In response to this, several projects attempting to address these issues have been initiated Legeai et al.
This area of research is likely to progress rapidly in the coming years. While climate change and the global food economy will continue to drive emergence of additional vector-borne bacterial pathosystems, the advent of genome editing, single-cell—omics, and interference RNA techniques will contribute to the identification of vector-borne bacterial phytopathogens and advances in our knowledge.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. We thank Aurelie Bak and MacKenzie Patton for helpful discussion and comments on earlier versions of this manuscript. National Center for Biotechnology Information , U. Front Plant Sci.
Published online Aug 9. Laura M. Perilla-Henao and Clare L. Author information Article notes Copyright and License information Disclaimer. Casteel, ude. Received May 14; Accepted Jul The use, distribution or reproduction in other forums is permitted, provided the original author s or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice.
No use, distribution or reproduction is permitted which does not comply with these terms. This article has been cited by other articles in PMC. DOCX 25K. Abstract Hemipteran insects are devastating pests of crops due to their wide host range, rapid reproduction, and ability to transmit numerous plant-infecting pathogens as vectors. Keywords: vector-borne bacteria, vascular bacteria, phloem, xylem, plant—insect interactions, plant—microbe interactions, leafhoppers, psyllids.
Introduction The plant vascular system is a rich source of nutrients and represents a transport pathway for colonizers. Redefining the Relationships Vector-Borne Bacteria Share With Hemipteran Insects Early studies of plant pathogens used microscopy, serological testing, and host inoculation to determine the etiological agents of diseases.
Persistence: Non-Persistent, Semi-persistent, or Persistent The transmission process of vector-borne viruses is categorized by two features: 1 the time period required by the vector for acquisition of the virus and inoculation of the virus, and 2 the retention time of viral particles in the vector Ng and Falk, Table 1 Vector-borne phloem limited plant pathogenic bacteria. Open in a separate window. The bacterial group is routinely culturable a or non-culturable b. Vector-Borne Bacteria: Dual Host Interactions All known vector-borne bacteria share certain biological features, including plant vascular tissue specialization, propagative relationships with vectors, and complete dependence on their hosts.
Xylem-Limited Vector-Borne Bacteria The only known xylem-limited bacterial pathogen that is also transmitted by hemipteran vectors is X. Table 2 Reported gene product or structure associated with host interaction for vector-borne bacteria. Phloem-Limited Vector-Borne Bacteria Diverse phylogenetic groups converge in phloem specialization and hemipteran transmission and it is hypothesized that those traits have been acquired independently multiple times over the course of bacteria evolution Orlovskis et al.
Spiroplasmas Spiroplasma spp. Liberibacter The genus Liberibacter spp. Approaches to Study Vector-Borne Bacteria The current understanding of pathogenicity mechanisms in vector-borne bacteria is largely influenced by the ability to culture those bacteria. Transcriptomics of Vector-Borne Bacteria in Their Hosts After potential pathogenicity factors are identified, functional validation is required.
Genetic Manipulation of Vector-Borne Bacterial Phytopathogens The first approach that permitted gene function discovery for vector-borne bacterial plant pathogens was the use of transposon mutagenesis with spiroplasmas in the early s Fletcher et al. Author Contributions CC conceived the project. CC and LP-H wrote the article.
Conflict of Interest Statement The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Acknowledgments We thank Aurelie Bak and MacKenzie Patton for helpful discussion and comments on earlier versions of this manuscript. References Abba S. BMC Genomics 15 : In Seawater: A spoon of seawater contains about a million viruses, making them the most plenteous natural substance in aquatic ecosystems.
They are useful in the disposal of saltwater and freshwater ecosystems. Viruses increase the number of Photosynthesis in Oceans and are effective for reducing the amount of carbon dioxide in the atmosphere by approximate 3 gigatonnes of carbon per year.
Human viruses, especially those that caused to deaths, can have larger negative economic effects. The virus destroys plenty of bacteria which useful for humans. Viruses can cause a destructive influence on human societies. They can be weaponized for biological warfare. Share This Post.
0コメント