Biology subjects

Kameoka, H.

Publications and source records attributed to Kameoka, H..

6 recordsLinked to original sources

bioRxiv2025

In vitro evaluation of protein-protein interactions in the rice KAI2 ligand signaling complex

KARRIKIN INSENSITIVE 2 (KAI2)/DWARF14-LIKE (D14L) plays key roles in land plant development, environmental responses, and the establishment of arbuscular mycorrhizal symbiosis, likely acting as the receptor for unidentified signaling molecules termed KAI2 ligands (KLs). KL perception by KAI2/D14L promotes DWARF3 (D3)/MORE AXILLARY GROWTH2 (MAX2) F-box protein-mediated ubiquitination of SUPPRESSOR OF MAX2 1 (SMAX1) proteins, thereby transducing the KL signals. Although genetic and in vivo assays have demonstrated the functions of these components, the biochemical details of their interactions remain elusive. Here we investigated physical interactions between rice D14L, D3, and OsSMAX1 in vitro using desmethyl germinone (dMGer), a recently developed KL analog. dMGer elicited KL responses in rice with higher activity and pathway specificity than a widely used KL analog (-)-GR24. dMGer, but not (-)-GR24, directly bound to D14L and promoted the interaction between D14L and D3 in vitro. The interaction between D14L and OsSMAX1 was also enhanced by dMGer. Furthermore, we identified the domain of OsSMAX1 that distinguishes it from its paralog DWARF53 (D53), which is associated with the strigolactone signaling complex. These findings propose a model of the interactions among KL signaling components and highlight the role of the ligand in the signaling complex.

plant biology↗

bioRxiv2021

An ancestral function of strigolactones as symbiotic rhizosphere signals

In flowering plants, carotenoid-derived strigolactones (SLs) have dual functions as hormones that regulate growth and development, and as rhizosphere signaling molecules that induce symbiosis with arbuscular mycorrhizal (AM) fungi. Here, we report the identification of bryosymbiol (BSB), a previously unidentified SL from the bryophyte Marchantia paleacea. BSB is also found in vascular plants, indicating that it is ancestral in land plants. BSB synthesis is enhanced at AM symbiosis permissive conditions and BSB deficient mutants are impaired in AM symbiosis. In contrast, the absence of BSB synthesis has little effect on the growth and gene expression. We show that the introduction of the SL receptor of Arabidopsis renders M. paleacea cells BSB-responsive. These results suggest that BSB is not perceived by M. paleacea cells due to the lack of cognate SL receptors. We propose that SLs originated as AM symbiosis-inducing rhizosphere signaling molecules and were later recruited as plant hormone.

plant biology↗

bioRxiv2020

Asymbiotic mass production of the arbuscular mycorrhizal fungus Rhizophagus clarus

Arbuscular mycorrhizal (AM) symbiosis is a mutually beneficial interaction between fungi and land plants and promotes global phosphate cycling in terrestrial ecosystems. AM fungi are recognised as obligate symbionts that require root colonisation to complete a life cycle involving the production of propagules, asexual spores. Recently it has been shown that Rhizophagus irregularis can produce infection-competent secondary spores asymbiotically by adding a fatty acid, palmitoleic acid. Further, asymbiotic growth can be supported using myristate as a carbon and energy source for their asymbiotic growth to increase fungal biomass. However, spore production and the ability of these spores to colonise host roots were still limited compared to co-culture of the fungus with plant roots. Here we show that a combination of two plant hormones, strigolactone and methyl jasmonate, induces production of a large number of infection-competent spores in asymbiotic cultures of Rhizophagus clarus HR1 in the presence of myristate and organic nitrogen. Inoculation of asymbiotically-generated spores promoted the growth of Welsh onions, as observed for spores produced by symbiotic culture system. Our findings provide a foundation for elucidation of hormonal control of the fungal life cycle and development of new inoculum production schemes.

microbiology↗

bioRxiv2019

Myristate as a carbon and energy source for the asymbiotic growth of the arbuscular mycorrhizal fungus Rhizophagus irregularis

Arbuscular mycorrhizal (AM) fungi, forming symbiotic associations with land plants, are obligate symbionts that cannot complete their natural life cycle without a host. Recently, fatty acid auxotrophy of AM fungi is supported by studies showing that lipids synthesized by the host plants are transferred to the fungi and that the latter lack genes encoding cytosolic fatty acid synthases (1-7). Therefore, to establish an asymbiotic cultivation system for AM fungi, we tried to identify the fatty acids that could promote biomass production. To determine whether AM fungi can grow on medium supplied with fatty acids or lipids under asymbiotic conditions, we tested eight saturated or unsaturated fatty acids (C12-C18) and two {beta}-monoacylglycerols. Only myristate (C14:0) led to an increase in biomass of Rhizophagus irregularis, inducing extensive hyphal growth and formation of infection-competent secondary spores. However, such spores were smaller than those generated symbiotically. Furthermore, we demonstrated that R. irregularis can take up fatty acids in its branched hyphae and use myristate as a carbon and energy source. Myristate also promoted the growth of Rhizophagus clarus and Gigaspora margarita. Finally, mixtures of myristate and palmitate accelerated fungal growth and induced a substantial change in fatty acid composition of triacylglycerol compared with single myristate application, although palmitate was not used as a carbon source for cell wall biosynthesis in this culture system. In conclusion, here we demonstrate that myristate boosts asymbiotic growth of AM fungi and can also serve as a carbon and energy source. Significance statementThe origins of arbuscular mycorrhizal (AM) fungi, which form symbiotic associations with land plants, date back over 460 million years ago. During evolution, these fungi acquired an obligate symbiotic lifestyle, and thus depend on their host for essential nutrients. In particular, fatty acids are regarded as crucial nutrients for the survival of AM fungi owing to the absence of genes involved in de novo fatty acid biosynthesis in the AM fungal genomes that have been sequenced so far. Here, we show that myristate initiates AM fungal growth under asymbiotic conditions. These findings will advance pure culture of AM fungi.

microbiology↗

bioRxiv2018

Cell type-specific regulation of nutrient absorption, metabolism and transfer in arbuscular mycorrhizal fungi

Arbuscular mycorrhizal fungi (AMF) establish symbiotic relationships with most land plants, mainly for the purpose of nutrient exchange. Many studies have revealed the regulation of absorption, metabolism, and transfer of nutrients in AMF and the genes involved in these processes. However, the spatial regulation of the genes among the structures comprising each developmental stage are not well understood. Here, we demonstrate the structure-specific transcriptome of the model AMF species, Rhizophagus irregularis. We performed an ultra-low input RNA-seq analysis, SMART-seq2, comparing five extraradical structures, germ tubes, runner hyphae, branched absorbing structures, immature spores, and mature spores. In addition, we reanalyzed the recently reported RNA-seq data comparing intraradical hyphae and arbuscules. Our analyses captured the distinct features of each structure and revealed the structure-specific expression patterns of genes related to absorption, metabolism, and transfer of nutrients. Of note, the transcriptional profiles suggest the distinct functions of branched absorbing structures in nutrient absorption. These findings provide a comprehensive dataset to advance our understanding of the transcriptional dynamics of fungal nutrition in this symbiotic system.

plant biology↗

bioRxiv2017

Evidence of non-tandemly repeated rDNAs and their intragenomic heterogeneity in Rhizophagus irregularis

Arbuscular mycorrhizal fungus (AMF) species are one of the most widespread symbionts of land plants. Our substantially improved reference genome assembly of a model AMF, Rhizophagus irregularis DAOM-181602 (total contigs = 210), facilitated discovery of repetitive elements with unusual characteristics. R. irregularis has only ten or eleven copies of complete 45S rDNAs, whereas the general eukaryotic genome has tens to thousands of rDNA copies. R. irregularis rDNAs are highly heterogeneous and lack a tandem repeat structure. These findings provide evidence for the hypothesis that rDNA heterogeneity depends on the lack of tandem repeat structures. RNA-Seq analysis confirmed that all rDNA variants are actively transcribed. Observed rDNA/rRNA polymorphisms may modulate translation by using different ribosomes depending on biotic and abiotic interactions. The non-tandem repeat structure and intragenomic heterogeneity of AMF rDNA/rRNA may facilitate adaptation to a various environmental condition including the broad host range.

genomics↗