International Webinar Series ”From Cellular Dynamics to Morphology III”

Program[Session I] Tue 22. Nov. 17:00-19:30 JST (UTC+9)
Chair: Yoshihisa Oda (Nagoya University), Yohei Kondo (ExCELLS)

Regulation of cellulose synthesis in land plants
Staffan Persson (University of Copenhagen, Denmark)Understanding self-organizing pattern on plant cell wall by mathematical analyses
Atsushi Mochizuki (Kyoto University, Japan)[Session II] Mon 28. Nov. 17:00-19:30 JST (UTC+9)
Chair: Keiji Nakajima (NAIST), Hidehiro Fukaki (Kobe University)

Auxin signaling: more than we have ever imaginedJiří Friml (Institute of Science and Technology, Austria)
Cell polarity establishment and maintenance by NPH3-like protein-mediated PIN cluster
formation in land plants
Satoshi Naramoto (Hokkaido University, Japan)
Low-auxin responsiveness is key to stem cell regulation in the liverwort Marchantia

polymorpha
Ryuichi Nishihama (Tokyo University of Science, Japan)[Session III] Wed 30. Nov. 17:00-19:30 JST (UTC+9)
Chair: Minako Ueda (Tohoku University), Takashi Ueda (NIBB)

Plant responses to water stress: back to the roots
Yang Zhao (Shanghai Center for Plant Stress Biology, CAS Center for Excellence in
Molecular Plant Sciences, China)
Deciphering the time- and space-dependent cellular dynamics of Arabidopsis root cap
Keiji Nakajima (Nara Institute of Science and Technology, Japan)

International Webinar Series ”From Cellular Dynamics to Morphology III”

[Session IV] Fri 2. Dec. 09:30-11:30 JST (UTC+9)
Chair: Takayuki Kohchi (Kyoto University), Motomu Endo (NAIST)

Dynamic Nutrient Signaling Networks in Plants
Kun-Hsiang Liu1,2, Ruiqiang Ye1,3, Jen Sheen1(1Massachusetts General Hospital/Harvard
Medical School, USA; 2 Northwest Agriculture & Forestry University, China; 3CAS Center
for Excellence in Molecular Plant Sciences, China)[Session V] Tue 6. Dec. 17:00-19:30 JST (UTC+9)
Chair: Hirokazu Tsukaya (University of Tokyo), Motomu Endo(NAIST)

Placing new walls: Molecular mechanisms of division plane control in plants
Katharina Bürstenbinder (Leibniz Institute of Plant Biochemistry, Germany)
Delivering intracellular materials: Roles and mechanisms of microtubule-based transport inplantsGohta Goshima (Nagoya University, Japan)[Session VI] Mon 19. Dec 17:00-19:30 JST (UTC+9)
Chair: Hidehiro Fukaki (Kobe University), Takayuki Kohchi (Kyoto University)

Spatial control of plant steroid receptors in plant adaption to climate stress
Ana I. Caño-Delgado (Center for Research in Agricultural Genomics, Spain)

Monophyllaea shoot system is composed of a single, indeterminate cotyledon with noadditional organ
Hirokazu Tsukaya (The University of Tokyo, Japan)

International Webinar Series ”From Cellular Dynamics to Morphology III”

[Session I] Tue 22. Nov. 17:00-19:30 JST (UTC+9)

Regulation of cellulose synthesis in land plants

Staffan Persson
University of Copenhagen, Denmark

All plant cells are surrounded by a cell wall that provides protection, neighbor adhesion andthe basis of morphology of plant cells. Cellulose is also a major raw material for manyindustries, including the paper, textile and fuel industries. Plant cell walls are mainly built bypolysaccharides of which cellulose typically constitute the major component. Cellulose ismade at the plasma membrane by large CELLULOSE SYNTHASE (CESA) protein
complexes that move forward in the membrane due to the immobilization of the nascentcellulose chains in the cell wall. The direction of the movement is steered by underlying
cortical microtubules. My group has outlined many aspects of cellulose synthesis and theprinciples of how the CESA complex is guided by microtubules. In this talk, I will highlightrecent progress in our knowledge of how the cellulose synthesis is controlled on different
levels, including transcriptional and post-translational controls.

International Webinar Series ”From Cellular Dynamics to Morphology III”

[Session I] Tue 22. Nov. 17:00-19:30 JST (UTC+9)

Understanding self-organizing pattern on plant cell wall bymathematical analyses

Atsushi Mochizuki
Kyoto University, Japan

In plant xylem vessels, thin cell wall regions called “cell wall pits” appear periodically. A seriesof studies by Oda et al. has revealed that ROP, a Rho-GTPase in plants, plays an importantrole in the periodic patterns of cell wall pits. On the plasma membrane surface, active ROP
forms a two-dimensional periodic distribution that determines the region corresponding tofuture cell wall pits. We hypothesized that the periodic patterns of ROPs are generated by
self-organization due to diffusional instability (Turing instability), and constructed areaction-diffusion model that takes into account the state-transition reaction of ROPs andtheir movement across the plasma membrane. Three possible models based on biological facts
are developed: (a) a basic model including only the state transition of ROP, (b) a negative
feedback model via conservation of the total amount of GEF and GAP, and (c) a positive
feedback model to the GEF binding reaction. Model (c) is based on the possibility of GEFs
forming dimers. We analyzed these models mathematically to determine the conditions underwhich the uniform distribution of ROPs is instabilized and a periodic pattern is generated. As
a result, we found that neither (a) the basic model nor (b) the negative feedback model canever form a periodic pattern, and that only (c) the positive feedback model can generate aperiodic pattern. In other words, the positive feedback to the GEF binding reaction is essential
for the formation of the periodic patterns of cell wall pits. Numerical simulations with various
parameter values were performed to quantitatively determine the conditions for the formationof the periodic patterns.

International Webinar Series ”From Cellular Dynamics to Morphology III”

[Session II] Mon 28. Nov. 17:00-19:30 JST (UTC+9)

Auxin signaling: more than we have ever imaginedJiří Friml
Institute of Science and Technology, Austria

The plant hormone auxin is a versatile intercellular signal influencing virtually all aspects ofplant life. It has a unique ability to be directionally transported within tissues forming local
auxin maxima or gradients that are central to many developmental processes mediated by
auxin. One of the key roles of auxin is adaptation of plant growth to gravity, where shoots
bend up and roots down. This paradox is based on opposite responses of these organs to thephytohormone auxin, which promotes cell expansion in shoots, while inhibiting it in roots via
an unclear signalling pathway and yet unknown downstream cellular mechanism
The well-established canonical auxin signalling involving the TIR1/AFB auxin
receptors, Aux/IAA repressors and ARF transcription factors acts in nucleus and mediates
gene transcription. However, auxin also triggers cellular responses within seconds or minutes,
too fast to rely on transcription. Part of the rapid responses is mediated by the nontranscriptional branch of the TIR1/AFB signalling, but others involve a yet completely
unknown mechanism.
Here I will present new and surprising insights into the mechanism of auxin signalling
including an ultrafast auxin-triggered protein phosphorylation response and previously
unsuspected aspects of TIR1/AFB auxin perception and downstream signalling.

Keywords: Auxin, Arabidopsis, root gravitropism, TIR1/AFB signalling
Acknowledgements: I gratefully acknowledge all present and past members of Friml groupand our excellent collaborators.

International Webinar Series ”From Cellular Dynamics to Morphology III”

[Session II] Mon 28. Nov. 17:00-19:30 JST (UTC+9)

Cell polarity establishment and maintenance by NPH3-likeprotein-mediated PIN cluster formation in land plants

Satoshi Naramoto
Hokkaido University, Japan

Cell polarity reflected by asymmetric distribution of proteins at the plasma membrane (PM)is essential for various cellular processes. PIN-FORMED (PIN) proteins are prominent
polarly localized PM proteins in seed plants and are proposed to undergo endocytic recycling
to establish and maintain polar localization of PIN proteins. The findings obtained so far
provide some conceptual framework of how PIN polarity is established and maintained.
However, there are still many open questions on the polar localization of PIN proteins. Oneof the main unresolved issues is the dynamics and behavior of PIN proteins at PMs. Here weshowed that at PMs PIN2 proteins form clusters that are organized into linear arrays parallel
to but non-overlapping with cortical microtubule and are also independent of endocyticmachinery. We also identified that NPH3-like protein MAB4 and its homolog MAB4/ENPlike (MEL)s induce PIN2 clustering, which in turn inhibit lateral diffusion and endocytosis of
PIN2 proteins to maintain polar localization of the PIN proteins. Furthermore, we determinedthat PIN clusters are structurally flexible protein complexes that are also present in bryophytes,
suggesting that PIN clusters are conserved across land plants. Our findings suggest a crucialrole for PIN clustering in its polar localization, and identify that plants have evolved a uniquemechanism for protein stabilization at specific PM regions as a basis for cell polarity
regulation.

International Webinar Series ”From Cellular Dynamics to Morphology III”

[Session II] Mon 28. Nov. 17:00-19:30 JST (UTC+9)

Low-auxin responsiveness is key to stem cell regulation in theliverwort Marchantia polymorpha

Ryuichi Nishihama
Tokyo University of Science, Japan

Development of all land plants is characterized with apical growth, by which new tissues andorgans are formed from stem cells residing in the apical meristem. Plants enlarge their bodies
by branching and also create new plants by regeneration, both of which involve amplificationof stem cells. The major phytohormone auxin is involved in these processes. Recent studies
revealed that the mechanism for auxin-mediated transcriptional regulation is highly conserved
throughout land plants. However, our knowledge on the roles of auxin in stem cell regulationin bryophytes is still limited. We address this issue with the liverwort Marchantia polymorpha.
When a thallus of M. polymorpha is bisected into the apical and basal halves, a newthallus regenerates only from the cut surface on the basal half. Therefore, auxin produced at
the meristem has been thought to inhibit regeneration. We show that the endogenous indole3-acetic acid level transiently and rapidly decreases at the cut site of decapitated explants,
which then triggers expression of the cellular reprogramming factor LOW-AUXINRESPONSIVE (MpLAXR) (Ishida et al., 2022). Even in intact plants, MpLAXR can be upregulated when auxin signaling is manipulated to diminish. Knockout of the sole auxin
receptor for the canonical nuclear pathway, MpTIR1, causes cell clump formation.
Transcriptome analysis revealed that the transcriptional response to auxin is largely impairedin the Mptir1 mutant cells and that their transcript profile has a stem cell property with

MpLAXR up-regulated, consistent with the low-auxin responsiveness of this gene (Suzuki etal., in revision). These findings highlight the key role of low-auxin responsiveness in stem cell
regulation. In this talk, we will also present our recent results and discuss gene regulatory
networks for this process.

International Webinar Series ”From Cellular Dynamics to Morphology III”

[Session III] Wed 30. Nov. 17:00-19:30 JST (UTC+9)

Plant responses to water stress: back to the roots

Yang Zhao
Shanghai Center for Plant Stress Biology, CAS Center for Excellence in
Molecular Plant Sciences, China

My research aims to decipher the stress-induced stimuli, identify sensors and core signaling
components, and illustrate growth regulation mechanisms, ultimately improving plant stress
tolerance. We have established scientific models and research systems for osmotic and salt
stress signaling. In past years, we discovered the plasma membrane-localized protein
OSMO1/BON1 controls early osmotic stress signaling (Current Biology, 2020). We have also
found that ABA-activated SnRK2s phosphorylate SWEET sucrose transporters andmicrotubule-binding protein SP2L, which mediates root growth and halotropism understressed conditions (Nature Plants, 2022; Developmental Cell, 2022). I will present these
discoveries, especially the cellular and molecular mechanisms of root halotropism.

International Webinar Series ”From Cellular Dynamics to Morphology III”

[Session III] Wed 30. Nov. 17:00-19:30 JST (UTC+9)

Deciphering the time- and space-dependent cellular dynamics
of Arabidopsis root cap

Keiji Nakajima
Nara Institute of Science and Technology, JapanThe root cap is a multi-layered tissue covering the tip of a plant root and directs root growthwith its unique functions such as gravity-sensing and secretion. To maintain its structure andfunctional integrity, the root cap cells continuously turnover through balanced proliferationof its inner stem cells and dehiscence of the outer mature cells. Such cellular turnover is seen
in many animal tissues, but is unique among plant tissues. To dissect genetic and molecularmechanisms underlying the periodic turnover of root cap cells, we developed a motion-tacking
confocal microscope system and used it to visualize both cellular and subcellular dynamics of
the Arabidopsis root cap, as well as their associated gene expression patterns. By combining
omics and genetic approaches, we have started to identify novel mechanisms thatspatiotemporally regulate cell separation and organelle rearrangement of the root cap
according to time and space.

International Webinar Series ”From Cellular Dynamics to Morphology III”

[Session IV] Mon 19. Dec 17:00-19:30 JST (UTC+9)

Dynamic Nutrient Signaling Networks in Plants

Kun-Hsiang Liu 1,2

Ruiqiang Ye 1,3

Jen Sheen 1

Massachusetts General Hospital/Harvard Medical School, USA
Northwest Agriculture & Forestry University, China
3
CAS Center for Excellence in Molecular Plant Sciences, China
1
2

Nutrient signaling is the most ancient and fundamental mechanism to regulate and sustain
life and acts to modulate cellular activities and organismal development by integrating withother intrinsic regulators and environmental cues. In contrast to the previously prevailingnotion that nutrients automatically feed into cellular metabolism and growth, nutrient
signaling mechanisms are complex for the tailored regulatory networks in diverse cell types,
tissues, and organs with specialized physiology, metabolism, and functions. Current modelsof regulatory networks in plant development have mainly focused on hormone and peptide
signaling. However, hormones and growth factors are ineffective in promoting growth without
nutrient signaling. To elucidate nutrient-mediated signaling mechanisms in plants, newexperimental approaches have been developed to circumvent limits due to gene redundancy
and mutant embryo lethality. We have developed targeted functional genomic screens,chemical genetic tools for lethal mutants, genomic profiling analyses, ultrasensitive Ca2+
ratiometric sensors, and PUP-IT-based proximity tagging screens for identifying new
nutrient sensing and signaling components in Arabidopsis thaliana as a reference plant. Our
efforts have led to a surprising molecular link in broad controls of plant development by
epigenomic reprogramming via glucose-driven TOR-FIE-PRC2 signaling. We also
discoveredthatspecificCa2+

sensorproteinkinases(CPKs)andNODULEINCEPTIONLIKE PROTEIN (NLP) transcription factors play pivotal roles in plant nitratesignaling in establishing shoot and root architecture. We have shown that the combinatorial
functions of NLP2,4,5,6,7,8,9 control primary nitrate responses that orchestrate thetranscriptional

network

topromotenitratetransport/assimilation,

metabolism

International Webinar Series ”From Cellular Dynamics to Morphology III”

reprogramming, and plant development. Our recent findings have identified NLP7 as apreviously unrecognized dual nitrate sensor and transcription activator, which enabled thecreation of the first genetically encoded split-fluorescent nitrate biosensor to visualize realtime intracellular nitrate dynamics over a broad concentration range in diverse organs inplants.

International Webinar Series ”From Cellular Dynamics to Morphology III”

[Session V] Tue 6. Dec. 17:00-19:30 JST (UTC+9)

Placing new walls: Molecular mechanisms of division plane
control in plants

Katharina Bürstenbinder
Leibniz Institute of Plant Biochemistry, Germany

Spatio-temporal control of cell division is crucial for morphogenesis of multicellular organisms,
and most particularly in plants, where cells are physically glued by cell walls that prevent cell
migration. To divide in the presence of rigid walls, cell division has undergone a switch froma cleavage-like mode, typically found in simple algae and animals, to an inside-out
mechanisms, in which new cell walls are inserted at the cell center and expand centrifugally
to fuse with the maternal cell wall. Two plant-specific cytoskeleton arrays, the preprophaseband (PPB) and phragmoplast play essential roles in division plane positioning and cell plate
formation. The assembly and dynamics of these mitotic microtubule arrays are controlled bymultiple functionally distinct classes of microtubule-associated proteins (MAPs). Although
functions of individual MAPs have been characterized in detail, it still is largely elusive how
networks of MAPs act in concert to coordinate the plant cytoskeleton. Here, I will present anddiscuss how a class of scaffold-like MAPs, termed IQ67 domain (IQD) proteins facilitates theassembly of MAPs and other interacting proteins at microtubules and membranes tocoordinate PPB formation, division plane set up, and cell plate positioning. Together, ouranalyses provide insights into molecular mechanisms of division plane control, and principles
and regulation of macromolecular complex assemblies that are essential for plant growth anddevelopment.

International Webinar Series ”From Cellular Dynamics to Morphology III”

[Session V] Tue 6. Dec. 17:00-19:30 JST (UTC+9)

Delivering intracellular materials: Roles and mechanisms of
microtubule-based transport in plants

Gohta Goshima
Nagoya University, Japan

Over the past decade, our laboratory has been delving deep into two long-standing questions
in plant microtubule biology: how do plant cells assemble the mitotic spindle in the absenceof centrosomes, and how do they execute microtubule-based transport without key molecularmotors found in animal cells? I will present what we have learnt on these issues, in particular
the identity of the long sought-after molecular motors of microtubule-based transport inplants.

International Webinar Series ”From Cellular Dynamics to Morphology III”

[Session VI] Mon 19. Dec 17:00-19:30 JST (UTC+9)

Spatial control of plant steroid receptors in plant adaption toclimate stress

Ana I. Caño-Delgado
Center for Research in Agricultural Genomics, Spain

Despite the massive amount of information gathered around the functions and mechanismsof Brassinosteroids (BRs) in plants, an important limitation persists in our knowledge of thissignaling pathway: almost all we know comes from observations on the BRI1 receptor pathway,that is essential for growth and development, and for which mutants are highly pleiotropic
and typically dwarf. Since the discovery of BRI1-like receptors (BRL1/3), we still do not reallygrasp what are their fundamental functions in plants. Twenty years of research have resumed
the analysis of BRLs as redundant BRI1 receptors with a marginal vascular expression andlack of apparent mutant phenotypes. Strikingly, our research takes a novel perspective to
explore the function of BRLs in Arabidopsis, to understand the inner working of this pathway.
Our recent findings showing that overexpression of BRL3-receptors confers drought
resistance invited to investigate the components of BRL3 pathway in Arabidopsis. Recently,
we have identified novel components in this vascular receptor pathway that are essential toplant adaption to climate stress. Our new data changes the paradigm for our present
understanding of BR signaling in plants and open new possibilities for producing climate
resilient crops. Our latest results will be presented at the seminar.
References:
Gupta, A., Rico-Medina, A. and Caño-Delgado, A.I. (2020). Science, 368(6488):26-269.
https://pubmed.ncbi.nlm.nih.gov/?term=caño-delgado

International Webinar Series ”From Cellular Dynamics to Morphology III”

[Session VI] Mon 19. Dec 17:00-19:30 JST (UTC+9)

Monophyllaea shoot system is composed of a single,
indeterminate cotyledon with no additional organ

Hirokazu Tsukaya
The University of Tokyo, JapanThe genus Monophyllaea belongs to the Gesneriaceae of Eudicot. Members of Monophyllaea
are distributed in the limestone regions of the tropics of Southeastern Asian and are known
as ‘one-leaf plants’. This is because they have only one leaf that grows indeterminately during
the vegetative phase. This indeterminate leaf originates from one of the two cotyledons thatspread evenly at germination. Shortly after germination, the two cotyledons compete witheach other and only one leaf survives to grow. Our surgical experiment showed that fate
determination occurs after germination. We recently revealed that skewed auxin
concentration between the two cotyledons and subsequent cytokinin levels are involved infate determination.
Instead one of cotyledons acquires indeterminacy of growth, no shoot apicalmeristem (SAM) activity is recognized between these cotyledons during the vegetative phase.
This queer shoot system is called ‘phyllomorph’. RNAseq analysis combined with whole
mount in situ hybridization analysis, we found that the SAM regulator STM and a leaf
meristem regulator AN3, both known in common plant species, are co-expressed in the basal
region of the indeterminately growing cotyledon. This fact suggests that phyllomorph, theindeterminate leaf, is a kind of a chimera of shoot and leaf. Based on our recent additional
data on the other SAM- and leaf meristem-related genes, we discuss possible regulatory
mechanisms of this unique phyllomorph system.