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.
questions of the project
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;
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.
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
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
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 graph.
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.
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.
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:
-Structural approaches informing on
the macromolecular complexes trafficking
inside plants and aphid vectors
-Molecular and cellular interactions
between virus and aphid vector
-Elucidate the specifics of the ecology
of multipartite viruses
events where results on the “nanovirus”
program will be communicated (either
virus-plant or virus-vector interactions)
Blanc S. Transmitted
plant viruses can affect performances
of starving aphid vectors. 13th International
Plant Virus Epidemiology Symposium.
6-10 June 2016, Avignon, France.
Invited key note lecture.
Blanc S. The strange biology of plant-infecting
multipartite viruses. New Frontiers
in Plant Biology. 15-17 June 2016,
Blanc S. Vector transmission: commonalities
and specificities in plant and animal
viruses. 6th European Congress of
Virology. 19-22 October 2016, Hamburg,
Blanc S. Nanoviruses have a non cell-autonomous
replication cycle. 8th International
Geminivirus Symposium and 6th International
ssDNA comparative Virology Workshop.
7-10 November 2016, New Delhi, India.
Invited Key note lecture
Invited Key note lecture. Member of
the International Advisory Committee.
Blanc S. Manipulation of insect vectors
by nanoviruses. 11th European Congress
of Entomology. 2-6 June 2018, Napoli,
Invited Key note lecture. Co-convenor
and co-chair of the session of “Symbiosis
and Insect vector Biology”.
Publication list of
the PI: S. Blanc (* corresponding
(current work, article submitted and
Blanc S*. Manipulation
of insect vectors by transmitted plant
viruses. Current Opinion in Insect
Science 2016. Invited review, in preparation
(due February 2016).
Sicard A, Michalakis Y, Gutierrez
S and S Blanc*. The
strange biology of multipartite viruses.
Sicard A, Pirolles E, Gutierrez S,
Yvon M, Michalakis Y and S Blanc*.
A pluricellular way of life for a
multipartite virus. In preparation
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 Sep 15;89(18):9683-8.
doi: 10.1128/JVI.00453-15. Epub 2015
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 July 15 ;89(19)
9719-26. doi: 10.1128/JVI.00780-15
Gutiérrez S, Pirolles E, Yvon
M, Baecker V, Michalakis Y and Blanc*
S: The multiplicity of cellular
infection changes depending on the
route of cell infection in a plant
virus. J Virol. 2015 Sep 15;89(18):9665-75.
Blanc* S and S Gutiérrez:
The specifics of vector transmission
of arboviruses of vertebrates and
plants. Curr Opin Virol. 2015 Jul
30;15:27-33. doi: 10.1016/j.coviro.2015.07.003.
Blanc* S, Drucker
M, Uzest M: Localizing viruses in
their insect vectors. Annu Rev Phytopathol
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 2013, 27:610-622.
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, 2:546-555.
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 2012, 8:e1003009.
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, 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
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
Brault V, Uzest M, Monsion B, Jacquot
E, Blanc S: Aphids
as transport devices for plant viruses.
C R Biol 2010, 333:524-538.
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
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, 84:4706-4713.
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
Blanc* S: Vector
transmission of plant viruses. In
Encyclopedia of Virology, edn 3rd.
Edited by Mahy BWJ, van regenmortel
MHV: Elsevier Ltd.; 2008:274-282.
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, 9:85.
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, 279:40-44.
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,
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
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),
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 Blanc* S :
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.
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, 92:65- 74.
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
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;
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 1999, 77:11-15.
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, 18:7077-7085.
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 1997, 231:141-147.
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
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.