Annunziata, R.

Atle, B.

Brembu, T.

Falciatore, A.

Finazzi, G.

Fortunato, A.

Huysman, M.J.J.

Lagomarsino, M.

Navarro, S.

Petroutsos, D.

Winge, P.

Annunziata, Rossella

Fortunato, Antonio E.

Navarro, Soizic Cheminant

Huysman, Marie J. J.

Petroutsos, Dimitri

Brembu, Tore

Winge, Per

Atle, Bones

Finazzi, Giovanni

Lagomarsino, Marco Cosentino

Falciatore, Angela

Archive Ouverte en Sciences de l'Information et de la Communication

THE CIRCADIAN CLOCK IN THE DIATOM PHAEODACTYLUM TRICORNUTUM

Open Marine Archive

Laboratory of Cell Cycles of Algae, Institute of
Microbiology CAS, Trebon 37981, Czech Republic
Green algae dividing by multiple ﬁssion are a diverse
group formed by species from unrelated genera. They
are connected by a common feature: mother cell under
optimal growth conditions divides into more than two
daughter cells. This organization of cell cycle represents
a potent evolutionary strategy allowing them to exploit
maximum of sun light during day for growth without
constraints from the cell cycle related processes. The
best developed model organism is Chlamydomonas
reinhardtii but other representatives include biotechno-
logically important algae such as Chlorella sp. and
Scenedesmus sp. Here, we will summarize the principles
governing the cell cycle regulation in algae dividing by
multiple ﬁssion. Further, we will present an example of
possible exploitation of the cell cycle mutants for the
study of coordination of cell cycle and response to DNA
damage. This work was supported by the GA CR (grant
no. 15-09231S), CAS (grant no. M200201205) and by
projects Algaman and Algain.
7OR.1
CELL-TYPE SPECIFIC PHOTORECEPTORS
AND ASSOCIATED LIGHT-SIGNALING
PATHWAYS IN THEMULTICELLULAR ALGA
VOLVOX CARTERI
Arash Kianianmomeni (kianian@uni-bielefeld.de)
Department of Cellular and Developmental Biology
of Plants, University of Bielefeld, Bielefeld 33615,
Germany
Photosynthetic organisms, e.g., plants including green
algae, use a sophisticated light-sensing system, com-
posed of primary photoreceptors and additional down-
stream signaling components, to monitor changes in the
ambient light environment towards adjust their growth
and development. Although a variety of cellular pro-
cesses, e.g., initiation of cleavage division and ﬁnal
cellular differentiation, have been shown to be light-
regulated in the green alga Volvox carteri, little is
known about the underlying light perception and signal-
ing pathways. This multicellular alga possesses at least
13 photoreceptors, i.e., one phototropin (VcPhot), one
UV-B photoreceptor (VcUVR8), four cryptochromes
(VcCRYa, VcCRYp, VcCRYd1 and VcCRYd2) and
seven members of rhodopsin-like photoreceptors
(VR1, VChR1, VChR2, VcHKR1, VcHKR2,
VcHKR3 and VcHKR4), which display distinct light-
dependent chemical processes based on their protein
architectures and associated chromophores. The study
of Volvox photoreceptors was almost always accompa-
nied by questions regarding their cell-type speciﬁc func-
tions, because they are mostly expressed in a cell-type
speciﬁc manner. This gives reason to believe that tran-
scriptome pattern of each cell type could change differ-
entially in response to environmental light. Comparison
of the gene expression proﬁles of the reproductive and
somatic cells reported revealed that distinct cell-type
speciﬁc light signaling pathways underlying gene
expression modulate appropriate transcript regulation
in response to light. Blue light tends to be effective to
accumulate transcripts in the somatic cells; while red
light leads to accumulate transcripts predominantly in
the reproductive cells. Thus, the data show that each cell
type has its own genetically predeﬁned light signaling
pathways to modulate expression of genes involved in
various cellular and metabolic processes including cir-
cadian rhythms and photosynthesis in response to envir-
onmental light.
7OR.2
THE CIRCADIAN CLOCK IN THE DIATOM
PHAEODACTYLUM TRICORNUTUM
Rossella Annunziata1 (rossella.annunziata@upmc.fr),
Antonio E Fortunato1 (antonio.fortunato@upmc.fr),
Soizic Cheminant Navarro1 (soizic.cheminant_na-
varro@upmc.fr), Marie JJ Huysman2 (mahuy@psb.
vib-ugent.be), Dimitri Petroutsos3 (dimitris.petrout-
sos@cea.fr), Tore Brembu4 (torebr@bio.ntnu.no), Per
Winge4 (per.winge@ntnu.no), Bones Atle4 (atle.
bones@bio.ntnu.no), Giovanni Finazzi3 (giovanni.
ﬁnazzi@cea.fr), Marco Cosentino Lagomarsino1
(marco.cosentino-lagomarsino@upmc.fr) and Angela
Falciatore1 (angela.falciatore@upmc.fr)
1Laboratory of Computational and Quantitative
Biology, Sorbonne Universités, UPMCUniv Paris 06,
UMR 7238, Paris 75006, France; 2Department of
Plant Systems Biology, VIB, Gent 9052, Belgium;
3Laboratoire Physiologie Cellulaire et Végétale,
CNRS, UMR 5168, Grenoble 38041, France and
4Department of Biology, Norwegian University of
Science and Technology, Trondheim 7491, Norway
The majority of living organisms evolved circadian
clocks, sophisticated mechanisms that synchronize
cells with the environmental periodic cues. Although
well studied in terrestrial plants and animals, only a
few examples of circadian clocks have been described
in marine organisms. Diatoms have exceptional adap-
tation capacities and exhibit circadian behaviors in
natural environments. Interestingly, no orthologous
of known circadian clock components have been
found in the sequenced genomes, suggesting the exis-
tence of a diatom speciﬁc clock. In order to reconstruct
diatom timing mechanisms, we completed high-reso-
lution physiological and transcriptomic analyses of
Phaeodactylum tricornutum cells grown in diurnal
light cycles and free-running conditions.We identiﬁed
Keynote and Oral Papers 64

24 genes showing robust rhythmic expression upon
the different treatments, including putative clock
inputs, oscillators and outputs, demonstrating a circa-
dian regulation of transcription. Using a mathematical
approach, we selected the most rhythmic
Transcription Factors (TFs) and explored their func-
tion by gene knockdown and over-expression. This
allowed the identiﬁcation of a ﬁrst clock component, a
bHLH-PAS TF, whose deregulation causes growth
impairment, loss of circadian gene expression and a
negative feedback loop effect on its own transcription.
Further characterizations of these and other TF
mutants will allow unraveling the circadian clock
architecture and its adaptive signiﬁcance in diatoms.
7OR.3
DESICCATION TOLERANCE IN
STREPTOPHYTIC GREEN ALGAE: NEW
INSIGHTS FROM TRANSCRIPTOMICS AND
FATTYACID METHYL ESTER (FAME)
ANALYSIS
Andreas Holzinger1 (Andreas.Holzinger@uibk.ac.at),
Martina Pichrtová2 (drosophila@centrum.cz),
Erwann Arc1 (Erwann.Arc@uibk.ac.at), Wolfgang
Stöggl3 (Wolfgang.Stoeggl@uibk.ac.at), Ilse
Kranner4 (Ilse.Kranner@uibk.ac.ats) and Burkhard
Becker5 (b.becker@uni-koeln.de)
1Instiute of Botany, Univeristy of Innsbruck,
Innsbruck 6020, Austria; 2Department of Botany,
Charles University in Prague, Prague 12801, Czech
Republic; 3Instiute of Botany, University of Innsbruck,
Innsbruck 6020, Austria; 4Institute of Botany,
University of Innsbruck, Innsbruck 6020, Austria and
5Botanical Institute, University of Cologne, Cologne
50674, Germany
Terrestrial green algae frequently experience desic-
cation. We investigated changes to the transcrip-
tome in Klebsormidiophyceae and fatty acid
composition in Zygnematophyceae upon desicca-
tion stress. At ~ 83% relative humidity (RH) the
effective quantum yield of photosystem II (Y II,
PAM 2500) dropped to zero between 4.5 and 7
hours in Klebsormidium crenulatum (SAG 2415).
The cells were able to recover 95% of the initial
values within 40 min. When desiccated over silica
gel (ﬁnal RH ~10%), Y II dropped to zero within
40-50 min and no immediate recovery of Y II was
observed. We analyzed the transcriptome under
moist and desiccated (2.5 h silica gel, RH ~
10%) conditions using RNAseq. The reference
transcriptome includes about 24,183 sequences
(1.5 million reads, 636 million bases). Over 7000
transcripts changed upon desiccation, 169 tran-
scripts were 10 fold upregulated, including
known factors involved in desiccation tolerance
(LEA, ERD), energy production, ROS metabolism
and enzymes involved in biosynthesis of rafﬁnose
family oligosaccarids (RFO), however many with-
out known function. 330 transcripts were comple-
tely suppressed. In Zygnema sp. from polar and
alpine habitats desiccation tolerance was only
observed in mature cultures that form akinetes, in
which Y II dropped to zero within 5-7 h at ~83%
RH. The transcriptomic analysis in Zygnema sp.
(SAG 2419) is underway. We analyzed the fatty
acid composition in Zygnema B, C and E. In all
samples the major fatty acids found were oleic and
linoleic acid, except in young cultures that also
contained palmitic and linolenic acids. We found
signiﬁcant differences in the fatty acid composition
between young cultures and all other samples,
however hardly any impact of the desiccation/
recovery experiment. We conclude that desiccation
tolerance occurs in both algal classes, but different
mechanisms (i.e. desiccation tolerance only after
maturation in Zygnema) may be involved.
7OR.4
THE STRUCTURE AND FUNCTION OF
COCCOLITH ASSOCIATED
POLYSACCHARIDES: IMPLICATIONS FOR
THEIR ROLE IN CALCIFICATION
Charlotte Elizabeth Walker1 (chawal@mba.ac.uk),
Colin Brownlee1 (cbr@mba.ac.uk), Toby Tyrrell2
(Toby.Tyrrell@soton.ac.uk) and Glen Wheeler1
(glw@mba.ac.uk)
1Cellular and Molecular Biology, Marine Biological
Association, Plymouth PL12PB, United Kingdom and
2Ocean and Earth Science, University of
Southampton, Southampton SO14 3ZH, United
Kingdom
Coccolithophores are globally distributed, unicellu-
lar marine algae belonging to the phylum
Haptophyta. Characterised by internally produced,
intricate calcite liths found on the cell surface, they
are biogeochemically important due to their role in
the transfer of carbon from the upper waters to
depth. Research has focused on the mechanisms
behind calciﬁcation, but exactly how and why
they calcify is still unknown. During lith production
in the unique Golgi-derived coccolith vesicle, poly-
saccharides are simultaneously produced and
extruded. These coccolith-associated polysacchar-
ides (CAPs) have been shown to play a role in
the regulation of calcium carbonate precipitation;
and therefore calciﬁcation. In this investigation we
looked at a range of species of coccolithophores
and their CAPs by direct observation and
Keynote and Oral Papers 65



The circadian clock in the diatom <i>Phaeodactylum tricornutum</i>

The circadian clock in the diatom <i>Phaeodactylum tricornutum</i>

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