Biology subjects

Kojima, C.

Publications and source records attributed to Kojima, C..

3 recordsLinked to original sources

bioRxiv2026

Species responses to nutrient loading promote resistance but not temporal stability in floating macrophyte communities

Determining the drivers of ecological stability amid accelerating global environmental change is a critical goal of contemporary ecology. Various candidate drivers have been suggested, with recent attention turning to response diversity--the variation among organism-environment responses. However, despite conceptual interest in response diversity as a driver of stability, there remain few field tests of this relationship. Using multi-species competitive communities of floating aquatic macrophytes as an experimental model for measuring temporal stability and response diversity to nutrient loading, we show that response diversity does not promote temporal stability of total macrophyte cover, but that communities with an uneven distribution of species responses were more resistant to an exogenous shock. To quantify macrophyte composition and growth dynamics from photographic time series of our experimental communities, we developed an open-source, scalable, machine learning workflow (LeafMosaic) capable of classifying four species from noisy field data including variable lighting, resolution, and plant morphology. We measured response diversity as the balance of positive and negative biomass growth responses to dissolved nitrate concentration, weighted by species relative contributions to biomass, and tested its effect on temporal stability and resistance to an unexpected pulse disturbance (a large typhoon that disrupted our outdoor mesocosms). Response imbalance predicted typhoon resistance, but species asynchrony and mean population stability best predicted community stability, with no direct or indirect effect of species responses. Overall, our results provide new experimental evidence for how the structure of species responses promotes stability, and we aim our LeafMosaic workflow to empower future field experiments using floating macrophytes to study response diversity and ecological stability.

ecology↗

bioRxiv2021

Biochemical propensity mapping for structural and functional anatomy of importin α IBB domain

Importin has been described as a nuclear protein transport receptor that enables proteins synthesized in the cytoplasm to translocate into the nucleus. Besides its function in nuclear transport, an increasing number of studies have examined its non-nuclear transport functions. In both nuclear transport and non-nuclear transport, a functional domain called the IBB domain (importin {beta} binding domain) plays a key role in regulating importin behavior, and is a common interacting domain for multiple binding partners. However, it is not yet fully understood how the IBB domain interacts with multiple binding partners, which leads to the switching of importin function. In this study, we have distinguished the location and propensities of amino acids important for each function of the importin IBB domain by mapping the biochemical/physicochemical propensities of evolutionarily conserved amino acids of the IBB domain onto the structure associated with each function. We found important residues that are universally conserved for IBB functions across organisms and families, in addition to those previously known, as well as residues that are presumed to be responsible for the differences in complex-forming ability between families and for functional switching.

cell biology↗

bioRxiv2021

Liquid-liquid phase separation of florigen activation complex induces flowering

Floral transition, regulated by the systemic action of the mobile florigen protein FLOWERING LOCUS T (FT), is essential for successful plant reproduction1. How FT controls downstream gene expression remains incompletely understood, although it relies on the florigen activation complex (FAC), a core component of FT function2-4. The FAC is a nucleus-localized transcriptional activator of genes encoding MADS-box transcription factors critical to reproductive development and consists of florigen FT; a scaffold 14-3-3 protein that is a key component for complex assembly; and FD, a basic leucine-zipper protein that recruits the FAC to DNA. Here we report that the FAC exhibits phase separation. In rice shoot apical meristem cells, rice florigen Heading date 3a (Hd3a) fused to the green fluorescent protein formed speckles in the nucleus. The FAC speckle is formed in a FAC-dependent manner in tobacco cells. Recombinant Hd3a, but not OsFD1, phase-separated in vitro, and this effect was enhanced in the presence of 14-3-3 protein. Furthermore, mutations affecting functionally important residues in the pocket region or C-terminal disordered region of Hd3a affected FAC phase separation, providing a biochemical framework for the proteins effect on flowering. The ability to form condensates via phase transition represents a previously unknown mechanism for gene activation by the FAC.

plant biology↗