Soybean dwarf virus is a plant virus that causes soybean dwarf disease, which belongs to the family Stereoviridae, which is mainly transmitted by aphid vectors and then causes severe disease on soybean seeds.
After soybean dwarf virus infection of soybean plants, it will cause plant deformity and dwarfing, yellowing, deformation and other symptoms of leaves and stems, slow growth of infected soybean plants, and reduction of the number of leaves, which seriously affects the yield and quality of soybeans.
Aphids are the main vector of soybean dwarf virus, infected aphids by sucking the sap of infected plants, the virus will be transmitted to the aphid's body, when these infected aphids again suck the sap of healthy plants, the virus will spread through the body fluids of aphids to new plants, resulting in new infections.
Therefore, controlling the spread of soybean dwarf virus population is very important for soybean planting and agricultural management, and measures to control aphid populations, select disease-resistant varieties, and rational farmland management are effective prevention and control strategies, as well as real-time monitoring of virus epidemics, early detection and control of virus transmission are also important measures.
Aphid transmission determined different aphid vectors SbDV
Many RNA viruses have genetically diverse populations in a single host, and their important biological characteristics may be related to the level of diversity, including adaptation, host specificity, and host range, and transferring viruses between hosts may result in changes in the level of diversity associated with the new host.
Understanding these interactions can help predict and prevent emerging viral diseases, and luteinizing viruses interact very specifically with aphid vectors.
Our team has shown that there may be a trade-off between viral adaptation and aphid transmission when soybean dwarf virus is infected, and in multiple successive aphid transmission assays, we examined viral titers in different aphid vectors, as well as levels of SbDV population diversity in different plant hosts.
The diversity of the SbDV population, revealing specific types of substitution and bias in genomic regions that may mutate between different hosts, and the selection of SbDV in soybeans may lead to a decrease in the efficiency of aphid recognition of viruses, which inhibits SbDV passage and regulates the movement of specific relationships between aphids and viruses, so we are going to isolate him.
SbDV isolate identification
Soybean dwarf virus (SbDV), a member of the luteinizing virus family found around the world, is limited to vascular phloem tissue in plants and transmitted in a persistent, non-reproductive manner via aphid vectors, which appears to have played a key role in the evolution and diversification of luteal virus.
SbDV is a single-stranded righteous RNA virus, and SbDV isolates have been found in many different plant hosts, such as white clover, underground clover, broad beans, peas, and lentils, however, it usually causes economically important diseases only in soybean crops.
There are several different isolates based on soybean symptoms, aphid vector specificity, and molecular composition, SbDV is common in clover but rarely causes soybean disease, however, SbDV infection in the field is limited and occurs only at the edge of the field, which involves a question of genetic diversity.
Population genetic diversity is an important part of a species' adaptation to a changing environment, and the error-prone replication, large population, and rapid replication associated with RNA viruses result in, even within a single host, genetically diverse populations.
However, unlike most animal viruses, most plant viruses need to be generalists to survive, and viral populations are complex and dynamic when levels of genetic diversity in a population respond to changes in selection pressure, and maintaining high levels of genetic diversity will favor the virus entering new environments.
Most comparative studies of viral evolution utilize a common sequence representing the average level of the entire viral population in a single host, but more detailed evolutionary dynamics studies that rely on genetic diversity will require more detailed genetic interpretation, and the level of diversity of plant viruses correlates with the size of their reported host range.
At the same time, plant viruses have different abilities to maintain population diversity in different hosts, for example, wheat striped mosaic virus does not change significantly in its diversity level when passaged in different cereal species.
Genetic bottlenecks also play an important role in viral evolution, leading to reduced genetic variation in viral populations, particularly transmission bottlenecks mediated by aphid vectors.
However, transmission bottlenecks in nature may not be as widespread as commonly believed, for example, the bottleneck in the transmission of genetic diversity within the dengue virus host is not particularly severe.
Similarly, in the case of certain plant RNA viruses, where co-infection is required to form fully functional units, multicomponent viruses may be considered for selection for transmission bottlenecks.
However, luteinizing virus interacts with aphid vectors very specifically, and selective specificity for luteinizing virus transmission can occur at least three cell sites, including the intestinal cell membrane, basement plasma membrane, and basal layer of the accessory salivary glands.
These specific recognition sites may be determined by multiple protein domains on the viral capsid and multiple cell surface receptors of aphid vectors.
Little is known about the evolutionary process and genetic diversity of luteinizing virus populations, which are highly vector-specific and host-tissue-specific, and transmission bottlenecks are considered to be key factors in reducing effective population size, thereby limiting the genetic diversity of flavivirus populations, and the efficiency of SbDV transmission is different for different aphid vectors.
SbDV transmission efficiency of different aphid vectors
To examine the efficiency of SbDV transmission in different aphid vectors, SbDV-MD6 was initially transmitted via clover to peas or soybeans, respectively, and then repeated to the same host plant for four consecutive transmissions by the same aphid species.
The propagation efficiency of each aphid was then determined after each transmission or passage, and the transmission efficiency of pea aphids fed continuously with peas in generations 1-4 was 30%, 40%, 60% and 50%, respectively, and after the first adaptive transmission from clover to peas, the passage efficiency of SbDV transmission to peas was improved.
In contrast, the transmission efficiency of SbDV in 1-4 generations was 25%, 16%, 8%, and 0%, respectively, in soybeans, the transmission of SbDV of Nepenthes pasteurized decreased with each subsequent passage, so does the ability of Aphids retain SbDV during transmission?
SbDV is present in aphids during serial propagation
To examine peas and Nepenthes pasteurii, the ability to obtain and retain SbDV by continuous passage, to acquire the virus, allow the aphids to feed on infected plants each passage, perform 24-h collection, and then analyze 25 aphids by RT-qPCR.
Each passage of 25 aphids was allowed to feed on red clover (non-host) for 2 days to clear the virus from the digestive tract, followed by a similar test.
By comparison, it was shown that SbDV efficiently entered the intestine during 24 h of consumption of peas or soybeans in peas and soybeans, and retained the virus in the blood cavity to clear the contents of the intestinal lumen after 48 h of consumption of red clover, and in the peas on the peas, the concentration of SbDV obtained after successive passages of the virus into the blood cavity was consistently high.
And in Nepenthes pasteurii pasteuria, SbDV accumulation during serial transmission is also high, but this is all to be expected because the concentration of SbDV in soybeans increases over time with continuous passage.
However, viral titers were significantly reduced after non-host feeding compared to peas, and after generation 3, although SbDV was still detected in the aphid blood cavity, they were unable to transmit SbDV.
To compare the acquisition and retention of SbDV in soybean aphids, SbDV-MD6 was established in soybeans by 3 consecutive passages using pasteurized aphids, and two different aphid vectors, pea aphids and glycine aphids, were then fed on infected soybeans for 48 h followed by non-host feeding for 48 h.
Both Aspergillus glycine and Aspergillus pea acquired and retained SbDV-MD6 in the blood cavity, and the low concentration of virus in glycine showed inefficient uptake and transport of SbDV from the intestinal lumen to the blood cavity after 48 h of non-host feeding.
However, both species acquired SbDV-MD6 in their blood chambers and had the genetic ability to transmit viruses, so the genetic diversity and mutation frequency of SbDV in plant hosts may also be different.
SbDV genetic diversity and mutation frequency in plant hosts
To determine the extent and structure of viral genetic diversity within SbDV hosts in different plant hosts by successive passages, we sequenced the clones of 9 samples, with SbDV-MD6 from infected clover used as inoculation sources, and young pea and soybean plants inoculated with aphid vectors and inoculation, respectively.
The first and last generation of two individually infected plants, used in our study, cloned the viral population, respectively, showed that most nonsynonymous and synonymous mutations occurred in replication-related genes in continuous transmission experiments.
They were cloned separately and analyzed for 11 to 20 clones of each fragment of each viral population, with very similar mutation frequencies between the passage lines of the two hosts, thus pooling mutation frequencies within passages.
Theoretically, each clone represents a unique viral RNA, and comparing the sequence of a viral clone with a shared sequence can provide a snapshot of the genetic diversity generated within a given viral population, using in vitro transcripts as template RNA for control reactions to estimate the level of variation introduced by transcription, RT, and thermocycling.
The mutation frequency is the number of bases that differ from the common sequence, divided by the total number of bases sequenced, for each plant treatment, sampling two plants, cloning and sequencing of two RT-PCR groups for each treatment will detect potential differences in the level of error introduced in independent RT-PCR.
And there were no significant differences between the sampled plants for any given passage, so cloning data from each passage was pooled, and the replication-related genes were used to examine the genetic diversity of individual infected plants, and after equilibrium, the level of genetic diversity within the host increased from an average of 0.08% for clover to 0.11% for peas and 0.12% for soybeans.
conclusion
Aphid vectors have multiple effects on the spread of soybean dwarf virus populations in soybean, aphids are important vectors of soybean dwarf virus and have high fecundity and migratory ability, it can quickly spread the virus to soybean plants, and aphid vectors enable soybean dwarf virus to spread over a large scale.
To reduce this impact, agricultural managers need to adopt effective prevention and control strategies, including monitoring virus transmission, controlling aphid populations, and using disease-resistant varieties, to minimize the occurrence of diseases and economic losses.