permaculture

[Lawrence London <lfljvenaura@gmail.com>]

http://bioscriptionblog.com/2019/06/16/plant-insect-viruses-infection/?fbclid=IwAR3HQu6r2y8hI92P44JO-vb6e10M8GWb3gKtpqzdW9vrErKXRLNMiVXEkM4
Plant and Insect Viruses Act Symbiotically In Host Infection

   -


   - Agrobacterium
   <http://bioscriptionblog.com/category/biotechnology/agrobacterium/>
   - Aphids <http://bioscriptionblog.com/category/pests/aphids/>
   - Biotechnology <http://bioscriptionblog.com/category/biotechnology/>
   - Diseases <http://bioscriptionblog.com/category/diseases/>
   - DNA Methylation
   <http://bioscriptionblog.com/category/mechanisms/dna-methylation/>
   - Epigenetics
   <http://bioscriptionblog.com/category/biotechnology/epigenetics/>
   - Evolution <http://bioscriptionblog.com/category/evolution/>
   - Evolutionary Biology
   
<http://bioscriptionblog.com/category/scientific-fields/evolutionary-biology/>
   - Genes <http://bioscriptionblog.com/category/genes/>
   - GFP
   
<http://bioscriptionblog.com/category/marker-genes/fluorescent-proteins/gfp/>
   - Insects <http://bioscriptionblog.com/category/insects/>
   - Miniposts <http://bioscriptionblog.com/category/miniposts/>
   - piRNA <http://bioscriptionblog.com/category/molecules/rna/pirna/>
   - Plant Pathology
   <http://bioscriptionblog.com/category/scientific-fields/plant-pathology/>
   - Plants <http://bioscriptionblog.com/category/plants/>
   - Proteins <http://bioscriptionblog.com/category/proteins/>
   - RNA interference
   <http://bioscriptionblog.com/category/biotechnology/rna-interference/>
   - Symbiosis <http://bioscriptionblog.com/category/behaviors/symbiosis/>
   - United States
   <http://bioscriptionblog.com/category/north-america/united-states/>
   - USDA <http://bioscriptionblog.com/category/organizations/usda/>
   - viRNA <http://bioscriptionblog.com/category/molecules/rna/virna/>
   - Virology
   <http://bioscriptionblog.com/category/scientific-fields/virology/>
   - Viruses <http://bioscriptionblog.com/category/viruses/>

When dealing with pathogens of plants, it is those of the viral kind in
conjunction with their vector pests that can prove to be the biggest
threats. Aphids, especially, are known for transmitting dozens of dangerous
viral diseases while also themselves managing to kill a host plant outright
through sucking up too much sap. Therefore, wiping out aphids is often a
top priority once they’ve been discovered in order to prevent a full blown
infestation. At the same time, however, plant viruses have a unique
relationship with vector insects and not in an entirely positive manner.
Plant Virus Dissemination

A team of researchers working at Cornell University and the USDA decided to
look into the effect plant viruses have on these insects and, in turn, how
this improved their ability to be transmitted to more plants. It is well
known that viruses are also to mount offensive molecular assaults on their
host plants, but the aphid-borne variety are also able to do the same to
their insect assistants, altering their biochemistry and even their
physiology in ways that benefit transmission. The primary line between
those that do and those that don’t is whether the plant virus is a
persistent, circulative type or a non-persistent, transient type.

The latter only interacts briefly with the aphids, allowing their virions
to be picked up by the mouthparts of the insect and then released when the
aphid goes to obtain sap from a new, uninfected plant. Since they have such
minimal interaction with aphids, they do essentially nothing to them in the
process. They are just a short vehicle to an end point. Persistent species,
on the other hand, are as their name suggests a more permanent feature.

These types of plant viruses enter into the circulatory system of the
aphids and remain a part of them for the rest of their lives. Every time
the aphids then consume sap from a plant, they transfer an amount of the
virus to the plant, spreading the infection further. It is the family of
Luteoviruses that exclusively use aphids as a vector like this, with potato
leafroll virus (PLRV) being the species the researchers were investigating.
Symbionts, Viruses, and RNA Expression

Known as the vector manipulation hypothesis for plant viruses, the
hypothesis has existed for over half a decade, based on prior physical
evidence of changes in insect vectors that transmit those viruses. On the
flip side, aphids also have positive endosymbionts, such as *Buchnera
aphidicola*, that help supply essential amino acids that the bugs can’t
otherwise obtain from their sap-based diet. While these symbionts would
have no reason to assist plant viruses in infecting aphids, it is possible
that the plant viruses affect the *Buchnera* symbiosis with aphids in some
way.

The team additionally wanted to see what relationship, if any, there was
between the plant viruses and the aphid virus *Myzus persicae
densovirus *(MpDNV).
Since both viruses need aphids to transmit themselves, but in very
different ways, their interaction could be positive or negative, but no
research into such a thing has been done before. Until this team began to
look into it.

The primary method of evidence collecting was based around small RNA (sRNA)
production and how RNA interference (RNAi) pathways were biochemically
altered by the creation of these sRNAs over time. Any viruses that begin to
replicate in the aphid tissues would themselves begin producing
virus-derived small interfering RNA (viRNA) to prevent the aphid immune
system from stopping them. Sequencing of all small RNAs would thereby show
how these changes occurred over time and how they affect gene expression of
aphids.
Difference in sRNA Production

When testing general expression differences, the researchers found that
piwi-interacting RNAs (piRNAs), a class of small RNAs that change gene
expression and epigenetic methylation of DNA, were altered or “primed” in
the aphid cells by the plant viruses and were able to cause germline
changes even without having any active plant interaction happening.
Similarly, when looking into the relationship with the symbiont, it was
shown that the relative amount of tRNAs produced to utilize the essential
amino acids provided by the bacteria varied when the aphid was also
infected with a plant virus. The changes, however, didn’t provide any
direct evidence toward how this alteration affected the aphid in general
and whether it was a good or bad change.

Lastly was the impact the plant virus has on insect virus uptake and
infection. It was already shown that the plant viruses themselves do have a
suppressive effect on the aphid antiviral immune system, but all the plant
viruses do this and not all of them show the same levels of insect virus
accumulation. So the scientists zeroed in on P0, a suppressor gene that
focuses on marking Ago1 for degradation. Ago1 is a member of the Argonaute
family of proteins and is involved in RNA interference and silencing,
something which could harm the plant viruses and so it is important for
them to minimize its activity.

After 3 days of exposure, the MpDNV levels were highest in the experimental
group made to eat leaves expressing the P0 protein. This effect was higher
than even the group exposed to the entire virus. The protein alone had a
stronger outcome. The team hypothesized that the protein may be altering
the antiviral immune system directly in the aphid cells and so expression
in leaf tissues gave it a more direct route to do so than having it have to
be applied by plant viruses.

Another facet of MpDNV infection is the forced formation of wings in times
outside of the migration season when the aphids normally grow them. The
virus often causes them to have wings permanently throughout the year,
increasing their mobility and thus greater contact with other aphids that
the MpDNV can infect. When looking into RNA levels, it was observed by the
researchers that the plant viruses like PLRV were helping to modulate this
wing expression and improving the ability for it to be enacted. This
results in greater winged morph variants being created than would otherwise
happen by probability within an infected population.
A Kaleidoscope of Interactions

There remains to be seen whether any further or deeper effects results from
a combined aphid infection with PLRV and MpDNV, but what is known thus far
is that their mutually beneficial alterations to aphid morphology and
biochemistry through genetic manipulation gives them both a greater chance
at transmitting themselves to future hosts.

These kinds of interactions on a microorganismal level are likely more
common than we currently know, but are especially difficult to tease out on
what individual alterations are done by each species. But we now have a
first look at such a thing in plant and insect viruses and that gives us
the clues and tools we need for our ongoing foray into the biological world
around us