Background and state
of the art
Three main categories of virus genome
structure and organization, independently
of whether the nucleic acid is single-
or double-stranded RNA or DNA, can
be distinguished. The “monopartite”
viruses have a single chromosome bearing
all genetic information and packaged
in a single virus particle. The “segmented”
viruses have two or more chromosomes,
which are all encapsidated together
in a single virion. Finally, the “multipartite”
viruses also have more than one chromosome,
from 2 to 10 depending on the viral
species, but each is encapsidated
individually in distinct virus particles.
Multipartite viruses are extremely
frequent in plants, where they induce
numerous diseases in major crops around
the world. They also infect fungi
and have recently been reported in
Because of this puzzling compartmentalization
of the genetic information of multipartite
viruses into several virus particles,
the functioning of their genome is
intricately linked to that of their
populations. Theoretical studies have
proposed putative advantages of such
viral systems, like enhanced stability,
replication and/or recombination/shuffling
of smaller nucleic acid segments;
the counterpart costs being the reduced
chances to infect new cells and new
hosts with at least one copy of each,
thus with no information loss. The
current view of the way multipartite
viral systems can be functional largely
suffers from the lack of experimental
data that would support any of the
proposed benefits or even the actual
existence of the above-mentioned cost
at new cell and host infection.
model and current results
have recently demonstrated that
the multipartite Faba bean necrotic
stunt virus (FBNSV, Family Nanoviridae,
Figure 1) reproducibly accumulates
its eight genes (or genome segments)
within host plants with different
and specific relative frequencies,
some genes being frequent and
others rare (Figure 2 top panel).
We here refer to the specific
pattern of the frequencies of
the eight segments as the “genome
formula” (Figure 2 bottom
panel). This discovery suggests
an unforeseen putative benefit
in multipartite viral systems,
that is the capability to differentially
control the copy number of each
gene/segment, which in turn drives
the virus population in the situation
of maximum costs, due to the increased
risk of losing rare segments.
1: Genome organization of nanoviruses
on the example of Faba bean
necrotic stunt virus (FBNSV).
Eight segments are circular
ssDNAs each around 1000 bases
: R encodes : Master-Rep assisting
replication of all segments,
S : coat protein CP separately
encapsidating all segments,
C : Clink resetting cell cycle,
M : movement protein MP mediating
in-plant virus migration, N
: nuclear shuttle protein NSP
regulating aphid transmission
(B. Gronenborn, pers. com.),
U1-U2-U4 have unknown functions.
CR-SL: common region stem loop.
2 : Gene Copy Number regulation
The relative frequency of each
FBNSV segment in Vicia faba
plants systemically infected
after inoculation by aphid vectors
is plotted in dark blue and
compared to that in agro-inoculated
plants (light blue on the left).
In Vicia faba, the frequency
of the segments was not affected
by the mode of inoculation (aphid-
versus agro-inoculation), as
indicated by ANOVA tests for
each of the eight segments.
The relative frequency of FBNSV
segments in Medicago truncatula
plants systemically infected
after inoculation by aphid vectors
is plotted in red. Vf-At1, Vf-At2,
Vf-At3, Mt-At1 and Mt-At2 results
from independent aphid-inoculation
experiments and the number of
infected plants in each set
(n) is indicated on the right.
A significant effect of the
host species could be detected
through ANOVA tests for 7 out
of 8 segments. (From Sicard
et al 2013)
The genome formulae of FBNSV
in Vicia faba (GF Vf) and in
Medicago truncatula (GFMt) were
respectively calculated by pooling
all Vf-At and Mt-At data sets,
and are indicated below the
The relative frequency of the
segments (segment name below
panels) was estimated by qPCR.
The rarest is arbitrarily considered
as 1 copy, and the copy number
of the others is represented
relative to it. Genome formula
in Vicia faba (V.f. green left),
Medicago truncatula (M.t. blue
center) and Acyrtosiphon pisum
(A.p. grey right). Adapted from
Sicard et al 2013 and Sicard
et al 2015.
of the project
We here develop a research program
that experimentally addresses
in parallel the relationship between
the various genome segments and
the population dynamics/genetics
of multipartite viruses, using
FBNSV as a model system. We investigate:
i) the link between the gene/segment
copy number (genome formula),
the regulation of gene expression,
and the expression of viral phenotypes
transmission by aphid vectors);
ii) the actual distribution of
distinct genomic segments in cells
of the host and of the vectors,
in order to reveal whether they
are all always together in individual
cells at all steps of the life
cycle, or whether the genetic
information can be temporarily
separated in distinct locations
of the host or vector, or even
in distinct hosts in the landscape
3 : Localization of distinct
genome segments in host plant
and aphid vector cells
The fluorescent labeling of
pairs of segments (here U2-red
and U4-green) demonstrates that
the segments do not necessarily
localize together in individual
cells of the host plant where
the virus replicates (left).
This suggests that the multipartite
viral systems can be functional
when distinct genes accumulate
in distinct cells and thus that
the system coordinates across
distinct cells in a tissue,
defining a pluricellular way
of life. In sharp contrast,
in the gut cells of insect vectors
(right), the virus does not
replicate and undergoes massive
transcytosis to traverse the
cellular gut barrier. We observe
countless cytoplasmic granules,
each containing all segments
of the tested pairs. This illustrates
a very intriguing counterintuitive
situation where all segments
accumulate together in cells
where no viral replication occurs
(aphid gut cells), whereas they
accumulate separately in distinct
cells where the virus replicates
(plant cells). Both images show
merged green and red channels,
and colocalization appears yellow.
Nucleus are DAPI-stained.
iii) the way ssDNA segments, mRNA
and proteins actually traffic within
hosts and vectors to investigate whether
the various segments can complement
each other only within cells or also
across cells; iv) the plastictity
of the genome formula in response
to environmental changes and its evolution
during adaptation to new host species.
This project provides key information
on the basic “way of life”
of multipartite viruses. In particular,
the proposed experiments inform (or
will inform) on both the putative
benefits and costs in these enigmatic
biological systems, for which decades
of theoretical studies led to the
recent conclusion that the current
conceptual framework of virology cannot
explain their existence.
Our ultimate goal is to generate
seminal results that will inspire
increased research efforts on multi-component
viral systems beyond multipartite
viruses plant, also on satellites,
defective interfering particles and
segmented viruses of animals.
The project is currently funded
by INRA SPE division and by French
ANR (ANR-nano project)
We are trying to attract additional
external funds to further develop
our project by investing more into:
-Our main model to acquire more details
and deep understanding of the biology
-other plant multipartite viral systems
-Satellites and defective interfering
particles of monopartite viruses
-Segmented viruses encapsidating their
segments in a non-selective manner
list of the PI: Stéphane Blanc
(* corresponding author)
Up coming stories:
- Blanc S and Y Michalakis (editors).
« Multicomponent viral systems
». We are preparing and will
edit a full section comprising 16
complementary review articles each
related to the topic. Current Opinion
in Virology 2019.
-Gallet R, Fabre F, Thébaud
G, Blanc S and Y Michalakis. Small
bottleneck size in Faba bean necrotic
stunt virus populations during aphid
transmission and plant colonization.
Manuscript in preparation.
-Sicard A, Pirolles E., Gallet R,
Vernerey M-S, Yvon M, Urbino C, Peterschmitt
M, Michalakis Y and S Blanc*. A pluricellular
way of life for a multipartite virus.
Manuscript in preparation
-Yvon M, Wright M, Michalakis Y and
S Blanc*. A plant virus induces a
switch in the investment of its insect
vector from fecundity to survival
in the absence of ressources. Manuscript
-Webster C, van Munster M, Monsion
B, Gargani D, Hoh F, Barthe P, Padilla
A, Bron P, Blanc S and M Uzest. Identification
of plant virus receptor candidates
in the stylets of aphid vectors. Manuscript
-Gallet* R, Fabre F, Michalakis Y,
and S Blanc* (2017). The number of
target molecules of amplification
step limits accuracy and sensitivity
in ultradeep-sequencing viral population
studies. J. Virol 2016, doi:10.1128/JVI.00561-17
-van Munster M, Yvon M, Vile D, Dader
B, Fereres A and S Blanc*. Water deficit
enhances the transmission of plant
viruses bu insect vectors. PLoS One
2017, 3;12(5). Doi:10.1371/journal
-Yvon M, Vile D, Brault V, Blanc S
and M van Munster. Drought reduces
transmission of turnip yellows virus,
an insect-vectored circulative virus.
Virus research 2017, doi: 10.1016/j.virusres.2017.07.009
-Webster C, Thillier M, Priolles E,
Cayrol B, Blanc S and M Uzest. Proteomic
composition of the acrostyle: Novel
approaches to identify cuticular proteins
involved in virus-insect interactions.
Insect Science 2017,
- Sicard A, Michalakis Y, Gutierrez
S and S Blanc*. The strange lifestyle
of multipartite viruses. PLoS Pathog
2016, 12(11): e1005819.
- Stéphane Blanc* and Yannis
Michalakis : Manipulation of hosts
and vectors by plant viruses and impact
of the environment. Current Opinion
in Insect Science 2016, 16:36–43.
- Blanc* S. & M. Uzest. Non-circulative
virus-vector interactions, In «Microbe-Arthropod
vector interactions» 2016, ed
J. Brown, American Phytopathological
-Roumagnac P, Granier M, Bernardo
P, Deshoux M, Ferdinand R, Galzi S,
Fernandez E, Julian C, Abt I, Filloux
D, Varsani A, Blanc S, Martin DP and
M. Peterschmitt: Alfalfa leaf curl
virus: An pahid transmitted geminivirus.
J Virol 2015, 89:9683–9688.
-Sicard A, Zeddam JL, Yvon M, Michalakis
Y, Gutierrez S, Blanc* S: Circulative
non propagative aphid-transmission
of nanoviruses: an oversimplified
view. J Virol 2015, 89:9719 –9726.
- Gutiérrez S, Pirolles E,
Yvon M, Baecker V, Michalakis Y and
S Blanc*: The multiplicity of cellular
infection changes depending on the
route of cell infection in a plant
virus. J Virol 2015, 89:9665–9675.
- Blanc* S and S Gutiérrez:
The specifics of vector transmission
of arboviruses of vertebrates and
plants. Current Opinion in Virology
2015, 15:27–33, doi.org/10.1016/j.coviro.2015.07.003
-Blanc* S, Drucker M, Uzest M: Localizing
viruses in their insect vectors. Annu
Rev Phytopathol 2014, 52:403-425.
-Bak A, Gargani D, Macia JL, Malouvet
E, Vernerey MS, Blanc S, Drucker M:
Virus factories of cauliflower mosaic
virus are virion reservoirs that engage
actively in vector transmission. J
Virol 2013, 87:12207-12215.
-Gutiérrez S, Michalakis Y,
Van Munster M, Blanc* S: Plant feeding
by insect vectors can affect life
cycle, population genetics and evolution
of plant viruses. Functional Ecology
-Martiniere A, Bak A, Macia JL, Lautredou
N, Gargani D, Doumayrou J, Garzo E,
Moreno A, Fereres A, Blanc* S and
M. Drucker*: A virus responds instantly
to the presence of the vector on the
host and forms transmission morphs.
Elife 2013, 2:e00183.
-Sicard A, Yvon M, Timchenko T, Gronenborn
B, Michalakis Y, Gutierrez S, Blanc*
S: Gene copy number is differentially
regulated in a multipartite virus.
Nature Commununications 2013, 4:2248.
-Gutierrez S, Michalakis Y, Blanc*
S: Virus population bottlenecks during
within-host progression and host-to-host
transmission. Curr Opin Virol 2012,
-Gutierrez S, Yvon M, Pirolles E,
Garzo E, Fereres A, Michalakis Y,
Blanc* S: Circulating virus load determines
the size of bottlenecks in viral populations
progressing within a host. PLoS Pathog
-Bak A, Irons SL, Martiniere A, Blanc
S, Drucker M: Host cell processes
to accomplish mechanical and non-circulative
virus transmission. Protoplasma 2011,
-Blanc* S, Uzest M and M Drucker.
New research horizon in vector-transmission
of plant viruses. Current Opinion
in Microbiology 2011, 14 :483-491
-Blanc* S, Drucker M: Functions of
virus and host factors during vector-mediated
transmission. In Recent Advances in
Plant Virology. Edited by Caranta
C, Aranda MA, Tepfer M, Lopez-Moya
JJ: Caister Academic Press; 2011:103-120.
-Martiniere A, Macia JL, Bagnolini
G, Jridi C, Bak A, Blanc S, Drucker
M: VAPA, an Innovative "Virus-Acquisition
Phenotyping Assay" Opens New
Horizons in Research into the Vector-Transmission
of Plant Viruses. PLoS One 2011, 6:e23241.
-Vuillaume F, Thebaud G, Urbino C,
Forfert N, Granier M, Froissart R,
Blanc S, Peterschmitt M: Distribution
of the phenotypic effects of random
homologous recombination between two
virus species. PLoS Pathog 2011, 7:e1002028.
-Brault V, Uzest M, Monsion B, Jacquot
E, Blanc S: Aphids as transport devices
for plant viruses. C R Biol 2010,
-Gutierrez S, Yvon M, Thebaud G, Monsion
B, Michalakis Y, Blanc* S: Dynamics
of the multiplicity of cellular infection
in a plant virus. PLoS Pathog 2010,
-Hoh F, Uzest M, Drucker M, Plisson-Chastang
C, Bron P, Blanc S, Dumas C: Structural
insights into the molecular mechanisms
of cauliflower mosaic virus transmission
by its insect vector. J Virol 2010,
-Khelifa M, Masse D, Blanc S, Drucker
M: Evaluation of the minimal replication
time of Cauliflower mosaic virus in
different hosts. Virology 2010, 396:238-245.
-Uzest M, Gargani D, Dombrovsky A,
Cazevieille C, Cot D, Blanc* S: The
"acrostyle": a newly described
anatomical structure in aphid stylets.
Arthropod Struct Dev 2010, 39:221-229.
-Martinière A, Gargani D, Uzest
M, Lautredou N, Blanc S, Drucker M:
A Role for Plant Microtubules in the
Formation of Transmission-specific
inclusion bodies of Cauliflower mosaic
virus. Plant J 2009, 58:135-146.
-Yvon M, Monsion B, Martin JP, Gutiérrez
S, Blanc* S: PCR-based amplification
and analysis of specific viral sequences
from individual plant cells. Journal
of Virological Methods 2009, doi:10.1016/j.jviromet.2009.04.016
-Blanc* S: Vector transmission of
plant viruses. In Encyclopedia of
Virology, edn 3rd. Edited by Mahy
BWJ, van regenmortel MHV: Elsevier
-Monsion B, Duborjal H, Blanc* S:
Quantitative Single-letter Sequencing:
a method for simultaneously monitoring
numerous known allelic variants in
single DNA samples. BMC Genomics 2008,
-Monsion B, Froissart R, Michalakis
Y, Blanc* S: Large bottleneck size
in Cauliflower Mosaic Virus populations
during host plant colonization. PLoS
Pathog 2008, 4:e1000174.
-Urbino C, Thebaud G, Granier M, Blanc
S, Peterschmitt M: A novel cloning
strategy for isolating, genotyping
and phenotyping genetic variants of
geminiviruses. Virol J 2008, 5:135.
-Blanc* S: Virus transmission-getting
out and in., vol 7. Edited by Heinlein
EWaM. Berlin-Heidelberg: Springer-Verlag;
-Brault V, Blanc S, Jacquot E: Comment
les pucerons transmettent des maladies
virales aux plantes. Biofutur 2007,
-Khelifa M, Journou S, Krishnan K,
Gargani D, Esperandieu P, Blanc S,
Drucker M: Electron-lucent inclusion
bodies are structures specialized
for aphid transmission of cauliflower
mosaic virus. J Gen Virol 2007, 88:2872-2880.
-Uzest M, Gargani D, Drucker M, Hebrard
E, Garzo E, Candresse T, Fereres A,
Blanc* S: A protein key to plant virus
transmission at the tip of the insect
vector stylet. Proc Natl Acad Sci
U S A 2007, 104:17959-17964.
-Jridi C, Martin JF, Marie-Jeanne
V, Labonne G, Blanc* S: Distinct viral
populations differentiate and evolve
independently in a single perennial
host plant. J Virol 2006, 80:2349-2357.
-Ballut L, Drucker M, Pugniere M,
Cambon F, Blanc S, Roquet F, Candresse
T, Schmid HP, Nicolas P, Gall OL,
et al.: HcPro, a multifunctional protein
encoded by a plant RNA virus, targets
the 20S proteasome and affects its
enzymic activities. J Gen Virol 2005,
-Froissart R, Roze D, Uzest M, Galibert
L, Blanc S, Michalakis Y: Recombination
every day: abundant recombination
in a virus during a single multi-cellular
host infection. PLoS Biol 2005, 3:e89.
-Moreno A, Hebrard E, Uzest M, Blanc*
S, Fereres A: A single amino acid
position in the helper component of
cauliflower mosaic virus can change
the spectrum of transmitting vector
species. J Virol 2005, 79:13587-13593.
-Plisson C, Uzest M, Drucker M, Froissart
R, Dumas C, Conway J, Thomas D, Blanc
S, Bron P: Structure of the mature
P3-virus particle complex of cauliflower
mosaic virus revealed by cryo-electron
microscopy. J Mol Biol 2005, 346:267-277.
-Blanc* S: Insect transmission of
viruses. In Microbe-vector interactions
in vector-borne diseases. Edited by
Gillespie SH, Smith GL, Osbourn A:
Cambridge University Press; 2004:42-61.
[Symposium S (Series Editor), vol
-Froissart R, Uzest M, Ruiz-Ferrer
V, Drucker M, Hebrard E, Hohn T, Blanc*
S: Splicing of Cauliflower mosaic
virus 35S RNA serves to downregulate
a toxic gene product. J Gen Virol
-Plisson C, Drucker M, Blanc S, German-Retana
S, Le Gall O, Thomas D, Bron P: Structural
characterization of HC-Pro, a plant
virus multifunctional protein. J Biol
Chem 2003, 278:23753-23761.
-Drucker M, Froissart R, Hebrard E,
Uzest M, Ravallec M, Esperandieu P,
Mani JC, Pugniere M, Roquet F, Fereres
A, and S Blanc* : Intracellular distribution
of viral gene products regulates a
complex mechanism of cauliflower mosaic
virus acquisition by its aphid vector.
Proc Natl Acad Sci U S A 2002, 99:2422-2427.
-Drucker M, German-Retana S, Espérandieu
P, Le Gall O, Blanc* S: Purification
of a viral protein from infected plant
tissues using the strep tag II affinity
tag. BioTech Intl. 2002, 14:16-18.
-Froissart R, Michalakis Y, Blanc*
S: Helper component-transcomplementation
in the vector transmission of plant
viruse. Phytopathology 2002, 92:576-579.
-Lett JM, Granier M, Hippolyte I,
Grondin M, Royer M, Blanc S, Reynaud
B, Peterschmitt M: Spatial and temporal
distribution of geminiviruses in leafhoppers
of the genus Cicadulina monitored
by conventional and quantitative polymerase
chain reaction. Phytopathology 2002,
-Palacios I, Drucker M, Blanc S, Leite
S, Moreno A, Fereres A: Cauliflower
mosaic virus is preferentially acquired
from the phloem by its aphid vectors.
J Gen Virol 2002, 83:3163-3171.
-Blanc* S, Hébrard E, Drucker
M, Froissart R: Molecular basis of
vector transmission : Caulimoviruses.
In Virus-Insect-Plant interactions.
Edited by Harris K, Smith OP, Duffus
JE: Academic Press; 2001:143-166.
-Hebrard E, Drucker M, Leclerc D,
Hohn T, Uzest M, Froissart R, Strub
JM, Sanglier S, van Dorsselaer A,
Padilla A, C. Dumas and S Blanc* :
Biochemical characterization of the
helper component of Cauliflower mosaic
virus. J Virol 2001, 75:8538-8546.
-Leh V, Jacquot E, Geldreich A, Haas
M, Blanc S, Keller M, Yot P: Interaction
between the open reading frame III
product and the coat protein is required
for transmission of cauliflower mosaic
virus by aphids. J Virol 2001, 75:100-106.
-Raccah B, Huet H, Blanc S: Potyviruses.
In Virus-Insect-Plant interactions.
Edited by Harris K, Duffus JE, Smith
OP: Academic Press; 2001:181-206.
-Héricourt F, Blanc S, Redeker
V, Jupin I: Evidence for phosphorylation
and ubiquitinylation of turnip yellow
mosaic virus RNA-dependent RNA polymerase
domain expressed in a baculovirus-insect
cell system. Biochem. J. 2000, 349:417-425.
-Blanc S, Dolja VV, Llave C, T.P.
P: Histidine-tagging and purification
of tobacco etch potyvirus helper component
protein. Journal of Virological Methods
-Hébrard E, Froissart R, Louis
C, Blanc* S: Les modes de transmission
des virus phytopathogènes par
vecteurs. Virologie 1999, 3:35-48.
-Leh V, Jacquot E, Geldreich A, Hermann
T, Leclerc D, Cerutti M, Yot P, Keller
M, Blanc* S: Aphid transmission of
cauliflower mosaic virus requires
the viral PIII protein. Embo J 1999,
-Blanc S, Ammar ED, Garcia-Lampasona
S, Dolja VV, Llave C, Baker J, Pirone
TP: Mutations in the potyvirus helper
component protein: effects on interactions
with virions and aphid stylets. J
Gen Virol 1998, 79 ( Pt 12):3119-3122.
-Blanc S, Lopez-Moya JJ, Wang R, Garcia-Lampasona
S, Thornbury DW, Pirone TP: A specific
interaction between coat protein and
helper component correlates with aphid
transmission of a potyvirus. Virology
-Blanc S, Schmidt I, Vantard M, Scholthof
HB, Kuhl G, Esperandieu P, Cerutti
M, Louis C: The aphid transmission
factor of cauliflower mosaic virus
forms a stable complex with microtubules
in both insect and plant cells. Proc
Natl Acad Sci U S A 1996, 93:15158-15163.
-Pirone TP, Blanc S: Helper-dependent
vector transmission of plant viruses.
Annu Rev Phytopathol 1996, 34:227-247.
-Kiss-Laszlo Z, Blanc S, Hohn T: Splicing
of cauliflower mosaic virus 35S RNA
is essential for viral infectivity.
Embo J 1995, 14:3552-3562.
-Schmidt I, Blanc S, Esperandieu P,
Kuhl G, Devauchelle G, Louis C, Cerutti
M: Interaction between the aphid transmission
factor and virus particles is a part
of the molecular mechanism of cauliflower
mosaic virus aphid transmission. Proc
Natl Acad Sci U S A 1994, 91:8885-8889.
-Blanc S, Cerutti M, Chaabihi H, Louis
C, Devauchelle G, Hull R: Gene II
product of an aphid-nontransmissible
isolate of cauliflower mosaic virus
expressed in a baculovirus system
possesses aphid transmission factor
activity. Virology 1993, 192:651-654.
-Blanc S, Cerutti M, Usmany M, Vlak
JM, Hull R: Biological activity of
cauliflower mosaic virus aphid transmission
factor expressed in a heterologous
system. Virology 1993, 192:643-650.
-Blanc S, Schmidt I, Kuhl G, Esperandieu
P, Lebeurier G, Hull R, Cerutti M,
Louis C: Paracrystalline structure
of cauliflower mosaic virus aphid
transmission factor produced both
in plants and in a heterologous system
and relationship with a solubilized
active form. Virology 1993, 197:283-292.