Biology subjects

Nonomura, K.-I.

Publications and source records attributed to Nonomura, K.-I..

5 recordsLinked to original sources

bioRxiv2024

Callose Deficiency Modulates Plasmodesmata frequency and the intercellular space In Rice Anthers

Fertilization relies on pollen mother cells able to transit from mitosis-to-meiosis to supply gametes. This process involves remarkable changes at the molecular, cellular and physiological levels including (but not limited to) remodelling of cell wall. During meiosis onset, cellulose content at the pollen mother cell walls gradually declines with the concurrent deposition of the polysaccharide callose in anther locules. We aim to understand the biological significance of cellulose-to-callose turnover in pollen mother cells walls using electron microscopic analyses of rice flowers. Our observations indicate that in wild type anthers, the mitosis-to-meiosis transition coincides with a gradual reduction in the number of cytoplasmic connections called plasmodesmata. A mutant in the Oryza sativa callose synthase GSL5, impaired in callose accumulation in premeiotic and meiotic anthers, displayed a reduction in plasmodesmata frequency among pollen mother cells and tapetal cells suggesting a role for callose in plasmodesmata maintenance. In addition, a significant increase in cell-cell distance between pollen mother cells and impaired premeiotic cell shaping was observed in the mutant. The results suggest that cellulose-to-callose turnover during mitosis-meiosis transition is necessary to maintain cell-to-cell connections and optimal intercellular spacing among anther locular cells explaining the regulatory influence of callose metabolism during meiosis in flowering plants. HighlightsO_LICellulose-to-callose switch during meiosis onset in pollen mother cell walls correlates with changes in cytoplasmic connections called plasmodesmata, among meiocytes and between meiocytes and surrounding somatic cells. C_LIO_LIA mutant in GSL5 (glucan synthase like 5) affects callose deposition but no other cell wall component (e.g., cellulose) in premeiotic and meiotic anthers, except at dyad stage. C_LIO_LIImpaired callose synthesis is proposed to alter plasmodesmata frequency, the extracellular spacing and the shaping of pollen mother cells during mitosis-to-meiosis transition. C_LIO_LIIncrease in plasmodesmata frequency negatively correlates with cell-cell distance between pollen mother cells in both wildtype and a callose mutant. C_LI

plant biology↗

bioRxiv2023

Leaf- and diverged shoot meristem programs shape the stem in rice

The stem is the shoot axis in seed plants and has been a primary target in breeding to regulate crop height. However, early processes of stem development remain elusive. Here we show that regulators for shoot meristems and leaves determine the node-internode pattern in rice. Mutants of KNOX1 genes OSH15 and OSH1, known to maintain shoot meristem indeterminacy1,2, showed dwarfism due to enlarged nodes and diminished internodes. These genes confine node differentiation by repressing leaf developmental regulator YABBY genes in internodal vasculatures. YABBY expression, which normally extends from leaves to nodes along vasculatures, promotes nodal vascular differentiation and limits stem elongation. It expands in knox1 mutants, and the loss of YABBY genes reverts their dwarfism. OSH15 also represses node-specific KNOX1 subclade genes OSH6 and OSH71 to allow internode elongation. Importantly, both YABBY and node-specific KNOX1 genes are required for pulvinus formation at the leaf base, further elaborating the nodal structure for gravitropism. Thus, intersections between leaf and sub-functionalized shoot meristem programs shape nodes and internodes along the stem. Phylogenetic analysis showed that KNOX1 sub-functionalization likely occurred in the progenitor of gymnosperms and angiosperms. Given that seed plants acquired their leaves independently from other vascular plant lineages3,4, the emergence of the node-internode pattern and KNOX1-YABBY regulatory module may be linked to seed plant leaf evolution.

plant biology↗

bioRxiv2023

Heat-shock inducible clonal analysis reveals the stepwise establishment of cell fates in the rice stem.

The stem, consisting of nodes and internodes, is one of the major organs in seed plants. In contrast to other organs, however, processes of stem development remain elusive, especially when nodes and internodes are initiated. By introducing an intron into the Cre recombinase gene, we established a heat-shock inducible clonal analysis system in a single binary vector and applied it to the stem in the flag leaf phytomer of rice. With detailed characterizations of stem development, we show that cell fate acquisition for each domain of the stem occurs stepwise. Cell fates for a single phytomer and the foot (non-elongating domain at the stem base) were established in the shoot apical meristem by one plastochron before the leaf initiation. The fate acquisition for the node occurred just before the leaf initiation, separating cell lineages for leaves and stems. Subsequently, fates for the axillary bud were established in early leaf primordia. Finally, cells committed to the internode emerged from, at most, a few tiers of cells when the stem epidermis was at the 12[~]25 celled stage. Thus, the internode is the last part of the stem whose cell fate is established. This study provides a groundwork to unveil underlying molecular mechanisms in stem development and a useful tool for clonal analysis, which can be applied to various species.

plant biology↗

bioRxiv2022

Rice GLUCAN SYNTHASE-LIKE5 promotes Callose deposition in Anthers to maintain proper Male Meiosis Initiation and Progression

Callose is a plant cell-wall polysaccharide whose deposition is spatiotemporally regulated in various developmental processes and environmental stress responses. Appearance of callose in premeiotic anthers is a prominent histological hallmark for the onset of meiosis in flowering plants, whose biological role in meiosis is unknown till date. Here we show that rice GLUCAN SYNTHASE LIKE5 (OsGSL5), a callose synthase, localizes on the plasma membrane of pollen mother cells (PMCs), and is responsible for biogenesis of callose in anther locules through premeiotic and meiotic stages. In osgsl5 mutant anthers mostly lacking callose deposition, aberrant PMCs accompanied by aggregated, unpaired or multivalent chromosomes were frequently observed, and furthermore, a considerable number of mutant PMCs untimely progress into meiosis compared to wild type PMCs. Immunostaining of meiosis-specific protein PAIR2 in premeiotic PMCs revealed precocious meiosis entry in osgsl5 anthers. The findings of this study bestows new knowledge on function of callose in controlling timing of male meiosis initiation and progression, in addition to roles in microsporogenesis, in flowering plants.

developmental biology↗

bioRxiv2021

Rice MEL2 regulates the timing of meiotic transition as a component of cytoplasmic RNA granules

Cytoplasmic RNA granules play important roles in gene expression at the post-transcriptional level. In this study, we found that the rice RNA-binding protein MEIOSIS ARRESTED AT LEPTOTENE2 (MEL2), which contributes to the control of meiotic entry timing, was a constituent of RNA granules, frequently associating with processing bodies and stress granules in the cytoplasm of premeiotic spore mother cells. MEL2 has four conserved domains and a large intrinsically disordered region, which is often responsible for formation and maintenance of granular structures. MEL2-like proteins with diverse domain structures are widely conserved in land plants and charophyte algae. In basal land plants, MEL2-like proteins are exclusively expressed in the sporophyte, which expresses meiotic genes, suggesting the functional conservation of MEL2 among land plant species. We propose here that MEL2 participates in post-transcriptional regulation of meiotic genes as a component of RNA granules to ensure proper timing of the meiotic transition.

plant biology↗