Biology subjects

Imaizumi, T.

Publications and source records attributed to Imaizumi, T..

3 recordsLinked to original sources

bioRxiv2018

Mechanistic model of temperature influence on flowering through whole-plant accumulation of FT

We assessed temperature influence on flowering by incorporating temperature-responsive flowering mechanisms across developmental age into an existing model. Temperature influences both the leaf production rate and expression of FLOWERING LOCUS T (FT), a photoperiodic flowering regulator, in leaves. The Arabidopsis Framework Model incorporated temperature influence on leaf growth but ignored the consequences of leaf growth on and direct temperature influence of FT expression. We measured FT production in differently aged leaves and modified the model, adding the mechanistic temperature influence on FT transcription, and linking FT to leaf growth. Our simulations suggest that in long days, the developmental timing (leaf number) at which the reproductive transition occurs is influenced by day length and temperature through FT, while temperature influences the rate of leaf production and the time (in days) the transition occurs. Further, we demonstrated that FT is mainly produced in the first 10 leaves in the Columbia ecotype, and that FT accumulation alone cannot explain flowering in conditions in which flowering is delayed. Our simulations supported our hypotheses that: 1) temperature regulation of FT, accumulated with leaf growth, is a component of thermal time, and 2) incorporating mechanistic temperature regulation of FT can improve model predictions in fluctuating temperatures.

plant biology↗

bioRxiv2018

Dawn and photoperiod sensing by phytochrome A

In plants, light receptors play a pivotal role in photoperiod sensing, enabling them to track seasonal progression. Photoperiod sensing arises from an interaction between the plants endogenous circadian oscillator and external light cues. Here, we characterise the role of phytochrome A (phyA) in photoperiod sensing. Our meta-analysis of functional genomic datasets identified phyA as a principal transcriptional regulator of morning-activated genes, specifically in short photoperiods. We demonstrate that PHYA expression is under the direct control of the PHYTOCHROME INTERACTING FACTOR transcription factors, PIF4 and PIF5. As a result, phyA protein accumulates during the night, especially in short photoperiods. At dawn phyA activation by light results in a burst of gene expression, with consequences for anthocyanin accumulation. The combination of complex regulation of PHYA transcript and the unique molecular properties of phyA protein make this pathway a sensitive detector of both dawn and photoperiod.\n\nSignificance statementThe changing seasons subject plants to a variety of challenging environments. In order to deal with this, many plants have mechanisms for inferring the season by measuring the duration of daylight in a day. A number of well-known seasonal responses such as flowering are responsive to daylength or photoperiod. Here, we describe how the photoreceptor protein phytochrome A senses short photoperiods. This arises from its accumulation during long nights, as happens during winter, and subsequent activation by light at dawn. As a result of this response, the abundance of red anthocyanin pigments is increased in short photoperiods. Thus, we describe a mechanism underlying a novel seasonal phenotype in an important model plant species.

plant biology↗

bioRxiv2017

Time-resolved Interaction Proteomics of the Putative Scaffold Protein GIGANTEA in Arabidopsis thaliana

The large, plant-specific protein GIGANTEA (GI) is involved in many physiological processes, mediating rhythmic, post-translational regulation in part through circadian and light regulation of GI RNA expression. GI binds several proteins implicated in the circadian clock, the control of photoperiodic flowering, and abiotic stress responses, and has co-chaperone activity. By extension, further interaction partners might mediate the less well-understood roles of GI but the number and rhythmicity of these interactors is unknown. Here, we seek potential interactors in a time-specific manner, using quantitative proteomics from a time series study of transgenic Arabidopsis thaliana plants constitutively expressing an epitope-tagged GI protein. Previously-identified, direct and indirect interactors of GI were detected but no further F-box proteins related to known GI partners ZTL/FKF1/LKP2. The predominantly non-rhythmic, interacting proteins were implicated in protein folding or degradation, metabolism and chromatin modification, including a small set of partners shared with other clock-related proteins. A transcription factor homologue that we name CYCLING DOF FACTOR 6 (CDF6) was shown to interact both with GI and the ZTL/FKF1/LKP2 proteins and to control photoperiodic flowering. Our results indicate the biochemical pathways, beyond circadian and flowering regulation, that might be affected by GIGANTEAs rhythmic, post-translational control.\n\nSignificance StatementSignificance statement of up to two sentences of no more than 75 words total;\n\nThe GIGANTEA protein of Arabidopsis was known for circadian and flowering functions, mediated by the FKF1/LKP2/ZTL family of GI-interacting, F-box proteins, then for a co-chaperone activity of unknown scope. We performed time-resolved, interaction proteomics, identifying CDF6 (At1g26790) as a morning-specific GI interactor that controls flowering time. Unlike FKF1 and CDF proteins, most of the 240 candidate partners were not rhythmically enriched. They link GI to proteostasis and metabolic functions that might mediate GIs physiological functions.

plant biology↗