Root PRR7 improves the accuracy of the shoot circadian clock through nutrient transport

The circadian clock allows plants to anticipate and adapt to periodic environmental changes. Organ- and tissue-specific properties of the circadian clock and shoot-to-root circadian signaling have been reported. While this long-distance signaling is thought to coordinate physiological functions across tissues, little is known about the feedback regulation of the root clock on the shoot clock in the hierarchical circadian network. Here, we show that the plant circadian clock conveys circadian information between shoots and roots through sucrose and K⁺. We also demonstrate that K+ transport from roots suppresses the variance of period length in shoots and then improves the accuracy of the shoot circadian clock. Sucrose measurements and qPCR showed that root sucrose accumulation was regulated by the circadian clock. Furthermore, root circadian clock genes, including PSEUDO-RESPONSE REGULATOR7 (PRR7), were regulated by sucrose, suggesting the involvement of sucrose from the shoot in the regulation of root clock gene expression. Therefore, we performed time-series measurements of xylem sap and micrografting experiments using prr7 mutants and showed that root PRR7 regulates K⁺ transport and suppresses variance of period length in the shoot. Our modeling analysis supports the idea that root-to-shoot signaling contributes to the precision of the shoot circadian clock. We performed micrografting experiments that illustrated how root PRR7 plays key roles in maintaining the accuracy of shoot circadian rhythms. We thus present a novel directional signaling pathway for circadian information from roots to shoots and propose that plants modulate physiological events in a timely manner through various timekeeping mechanisms

Role of the Arabidopsis Glucose Sensor Hexokinase1 (HXK1) in seedling establishment

Light energy serve as primary substrates for photosynthetic sugar production in plant metabolic maintenance. In addition, light also functions as a crucial environmental cue initiating a series of signal transduction cascades downstream to the photoreceptors. Limited knowledge exists on the molecular connections integrating the metabolic and photoreceptor signalling pathways. The primary focus of this thesis is the plant glucose receptor Hexokinase1 (HXK1). Arabidopsis HXK1 performs a dual function 1) an enzymatic role in glycolysis catalysing glucose phosphorylation to generate glucose-6-phosphate (G6P) and 2) a transcriptional repressor role in response to exogenous sugar. While the enzymatic role required for ATP production during respiration is conserved across biological systems, the sugar induced nuclear signalling role has only been identified in yeast and Arabidopsis. In this thesis, I show that HXK1 operates during nutrient limiting conditions such as extended periods of darkness or suboptimal light in seedlings. A first-ever RNAseq enabled us to gain insights into the mutant transcriptome. Energy demanding pathways were downregulated and carbon starvation induced Branched Chain Amino Acid (BCAA) degradation pathway is upregulated as an alternate energy source. Supplying Glucose-6-Phosphate (G6P – HXK1 enzymatic endproduct) restored the mutant phenotype and the C starvation response during nutrient limited conditions. This highlights the requirement of HXK1 enzyme rather than the signalling component during seedling establishment. Nuclear HXK1 operates as a transcriptional repressor in response to exogenous sugar. It is postulated to function during feedback inhibition of photosynthetic genes. However, our data indicates that this does not appear to be the case when endogenous sugars are naturally elevated in seedlings. Further, I present preliminary data on the potential feedback regulation by HXK1Overpression (HXK1OX) in blue and red light signalling pathway. HXK1 exerts a negative control on blue light mediated photomorphogenesis. Red light negates this effect in a PHYB dependent manner. Although the transcriptomes are reflective of the phenotype, the molecular mechanism behind this response is unknown. Taken together, my thesis discovers novel facets of HXK1 during seedling establishment

A guiding role of the Arabidopsis circadian clock in cell differentiation revealed by time-series single-cell RNA sequencing

Circadian rhythms and progression of cell differentiation are closely coupled in multicellular organisms. However, whether establishment of circadian rhythms regulates cell differentiation or vice versa has not been elucidated due to technical limitations. Here, we exploit high cell fate plasticity of plant cells to perform single-cell RNA sequencing during the entire process of cell differentiation. By analyzing reconstructed actual time series of the differentiation processes at single-cell resolution using a method we developed (PeakMatch), we find that the expression profile of clock genes is changed prior to cell differentiation, including induction of the clock gene LUX ARRYTHMO (LUX). ChIP sequencing analysis reveals that LUX induction in early differentiating cells directly targets genes involved in cell-cycle progression to regulate cell differentiation. Taken together, these results not only reveal a guiding role of the plant circadian clock in cell differentiation but also provide an approach for time-series analysis at single-cell resolution

Support for UNRWA's survival

The United Nations Relief and Works Agency for Palestine Refugees in the Near East (UNRWA) provides life-saving humanitarian aid for 5·4 million Palestine refugees now entering their eighth decade of statelessness and conflict. About a third of Palestine refugees still live in 58 recognised camps. UNRWA operates 702 schools and 144 health centres, some of which are affected by the ongoing humanitarian disasters in Syria and the Gaza Strip. It has dramatically reduced the prevalence of infectious diseases, mortality, and illiteracy. Its social services include rebuilding infrastructure and homes that have been destroyed by conflict and providing cash assistance and micro-finance loans for Palestinians whose rights are curtailed and who are denied the right of return to their homeland

Phytochrome-mediated regulation of cell division and growth during regeneration and sporeling development in the liverwort Marchantia polymorpha.

First online: 05 April 2015Light regulates various aspects of development throughout the life cycle of sessile land plants. Photoreceptors, such as the red (R) and far-red (FR) light receptors phytochromes, play pivotal roles in modulating developmental programs. Reflecting high developmental plasticity, plants can regenerate tissues, organs, and whole bodies from varieties of cells. Among land plants, bryophytes exhibit extraordinary competency of regeneration under hormone-free conditions. As an environmental factor, light plays critical roles in regeneration of bryophytes. However, how light regulates regeneration remains unknown. Here we show that using the liverwort Marchantia polymorpha, which contains a single phytochrome gene, the phytochrome regulates re-entry into the cell cycle and cell shape in newly regenerating tissues. Our morphological and cytological observations revealed that S-phase entry of G1-arrested epidermal cells around the midrib on the ventral surface of thallus explants was greatly retarded in the dark or under phytochrome-inactive R/FR cycle irradiation conditions, where, nevertheless, small, laterally narrow regenerants were eventually formed. Thus, consistent with earlier descriptions published over a century ago, light is not essential for, but exerts profound effects on regeneration in M. polymorpha. Ventral cells in regenerants grown under R/FR cycle conditions were longer and narrower than those under R cycle. Expression of a constitutively active mutant of M. polymorpha phytochrome allowed regeneration of well grown, widely expanded thalli even in the dark when sugar was supplied, further demonstrating that the phytochrome signal promotes cell proliferation, which is rate-limited by sucrose availability. Similar effects of R and FR irradiation on cell division and elongation were observed in sporelings as well. Thus, besides activation of photosynthesis, major roles of R in regeneration of M. polymorpha are to facilitate proliferation of rounder cells through the phytochrome by mechanisms that are likely to operate in the sporeling

Co-option of a photoperiodic growth-phase transition system during land plant evolution.

陸上植物の季節に依存して花を咲かせる仕組みの起源を紐解く. 京都大学プレスリリース. 2014-04-22.Photoperiodic control of the phase transition from vegetative to reproductive growth is critical for land plants. The GIGANTEA (GI) and FLAVIN-BINDING KELCH REPEAT F-BOX1 (FKF1) protein complex controls this process in angiosperms. However, little is known about how plants evolved this regulatory system. Here, we report that orthologues of GI and FKF1 are present in a basal plant, the liverwort Marchantia polymorpha, and describe the molecular interaction between their products. Knockout of either the GI or FKF1 orthologue completely abolishes the long-day-dependent growth-phase transition in M. polymorpha. Overexpression of either gene promotes growth-phase transition, even under short-day conditions. Introduction of the GI orthologue partially rescues the late-flowering phenotype of the Arabidopsis thaliana gi mutant. Our findings suggest that plants had already acquired the GI-FKF1 system to regulate growth-phase transition when they colonized land, and that this system was co-opted from gametophyte to sporophyte generation during evolution

Ultrafast Dynamic Contrast-enhanced MRI of the Breast : How Is It Used?

Ultrafast dynamic contrast-enhanced (UF-DCE) MRI is a new approach to capture kinetic information in the very early post-contrast period with high temporal resolution while keeping reasonable spatial resolution. The detailed timing and shape of the upslope in the time-intensity curve are analyzed. New kinetic parameters obtained from UF-DCE MRI are useful in differentiating malignant from benign lesions and in evaluating prognostic markers of the breast cancers. Clinically, UF-DCE MRI contributes in identifying hypervascular lesions when the background parenchymal enhancement (BPE) is marked on conventional dynamic MRI. This review starts with the technical aspect of accelerated acquisition. Practical aspects of UF-DCE MRI include identification of target hypervascular lesions from marked BPE and diagnosis of malignant and benign lesions based on new kinetic parameters derived from UF-DCE MRI: maximum slope (MS), time to enhance (TTE), bolus arrival time (BAT), time interval between arterial and venous visualization (AVI), and empirical mathematical model (EMM). The parameters derived from UF-DCE MRI are compared in terms of their diagnostic performance and association with prognostic markers. Pitfalls of UF-DCE MRI in the clinical situation are also covered. Since UF-DCE MRI is an evolving technique, future prospects of UF-DCE MRI are discussed in detail by citing recent evidence. The topic covers prediction of treatment response, multiparametric approach using DWI-derived parameters, evaluation of tumor-related vessels, and application of artificial intelligence for UF-DCE MRI. Along with comprehensive literature review, illustrative clinical cases are used to understand the value of UF-DCE MRI