Biology subjects

Kamakura, T.

Publications and source records attributed to Kamakura, T..

4 recordsLinked to original sources

bioRxiv2026

Comprehensive functional mapping of accessory chromosomes identifies a dominant virulence-regulator paralog in tomato wilt pathogen

Accessory chromosomes (ACs) serve as flexible genomic compartments that facilitate rapid adaptive evolution in eukaryotic microbes. In the tomato wilt pathogen Fusarium oxysporum f. sp. lycopersici, ACs are essential for virulence and host specificity; however, their structural complexity and functional redundancy have hindered a systematic characterization of their distinct roles. Here, we established a CRISPR/Cas9-based chromosomal dissection platform to generate a comprehensive functional map of pathogenicity determinants within ACs. Using this platform, we successfully generated a library of 36 large deletion mutants across the approximately 10 Mb putative AC region, enabling a chromosome-scale functional characterization of these compartments. A systematic screen of this library identified seven discrete AC segments that are indispensable for full virulence toward tomato. High-resolution chromosomal dissection of one virulence-associated segment through iterative subdivision and targeted gene disruption revealed that FTF1a-1, a single member of the Fusarium transcription factor 1 (FTF1) family that originated from the duplication of core-chromosomal virulence gene FTF2 into the AC region, functions as a dominant regulator of virulence. Given that the FTF1a-3 paralog contributes only marginally to virulence and the deletion of other paralogs does not markedly affect disease development, our findings demonstrate a functional hierarchy within the duplicated FTF1 gene family. These results imply that neofunctionalization of virulence genes within plastic fungal genomes promotes hyper-virulence and drives host-specific adaptation in F. oxysporum.

microbiology↗

bioRxiv2025

Resistance to Atrial Fibrillation Domestication and Mitochondrial Dysfunction in Sheep: a potential key role of the TCA Cycle and mitochondrial redox state

BackgroundAtrial fibrillation (AF) often progresses from paroxysmal to more stable forms. It is well-recognized that patients vary in their AF progression, but underlying mechanisms remain unclear. This work, performed in a sheep AF-model, aimed to identify atrial redox and energetic status differences between animals developing stable AF (AF-S) versus those resistant to AF-stabilization (AF-R). MethodsAF was monitored with telemetry and maintained with bursts of atrial tachystimulation whenever sinus rhythm resumed. Electrophysiological remodeling was assessed via contact mapping. Structural remodeling was described by histology. Proteomic, metabolomic, enzymatic and bioenergetic remodeling were evaluated using frozen left atrial appendage (LAA) tissues and isolated LAA mitochondria. Healthy young rats were used to investigate if an induced metabolic challenge could stabilize AF episodes upon transesophageal atrial tachypacing challenge. ResultsAF-S sheep developed stable AF (>24-hours self-sustained) after 13 days on average, whereas AF-R sheep failed to develop self-sustained AF despite 120 days of electrically-maintained AF. Contact mapping and histological analysis revealed similar electro-structural remodeling in both groups. Metabolic analysis showed significant differences in tricarboxylic acid (TCA) cycle enzymes activities and a 45% increase in AF-S LAA succinate content versus AF-R. AF-S mitochondria showed abnormal mitochondrial succinate oxidation, associated with a significant 20% decrease in ATP synthesis rate, 22% increase in ROS emission and mitochondrial inner membrane hyperpolarization. The ratios of ATP to ADP, NAD+ to NADH, and Complex I/II were disturbed in AF-S compared to AF-R. Calculated mitochondrial NAD+ to NADH ratios suggest a reduced state of in-vivo AF-R mitochondria compared to the oxidized state of AF-S. Exogenous succinate was metabolized when incubated with rat atrial cardiomyocytes and altered redox balance, while intravenous succinate stabilized atrial arrhythmias induced by tachypacing in vivo. ConclusionsSheep resistant to AF-progression showed specific TCA cycle, energetic and redox adaptations compared to animals that developed self-sustained AF. In this animal model, mitochondrial TCA cycle remodeling and associated redox and energetic responses determined the resistance to AF domestication, with potential relevance to identify new mechanistic determinants of AF progression in humans.

pathology↗

bioRxiv2024

Extensive intrachromosomal duplications in a virulence-associated fungal accessory chromosome

Filamentous fungi have evolved compartmentalized genomes consisting of conserved core regions and dynamic accessory regions, which aid the adaptation to changing environments including the interaction with host organisms. In the Fusarium oxysporum species complex, accessory regions play an important role during infection and it has been reported that these regions undergo extensive duplications, however, it is currently unknown how such duplications shape accessory regions. Moreover, the function of accessory regions apart from encoding virulence effectors is not completely understood. Here we determined the karyotype of F. oxysporum Tropical Race 4 (TR4), which causes the ongoing pandemic of Fusarium wilt of banana (FWB). We show that the single accessory chromosome of TR4 isolate II5 has undergone extensive intrachromosomal duplications, resulting in triplication of the chromosome size compared to other closely related TR4 strains. By obtaining mutant strains that have lost the accessory chromosome, we demonstrate that this chromosome is dispensable for vegetative growth but is required for full virulence on banana. Lastly, we found that the loss of chromosome 12 co-occurs with structural rearrangements of core chromosomes, which are generally co-linear between members of the F. oxysporum species complex. Together, our results provide new insights into the chromosome dynamics of the banana infecting TR4 lineage of the F. oxysporum species complex. SignificanceFusarium oxysporum is a major fungal plant pathogen that causes vascular wilt disease on a wide variety of agronomically important crops. A current epidemic of Fusarium wilt of banana (FWB), caused by tropical race 4 (TR4), poses a major threat to global banana production and threatens food security in tropical and subtropical regions where banana is an important staple crop. Controlling TR4 requires a better understanding of the molecular mechanisms underlying pathogenicity, including the evolution of pathogenicity-related accessory regions. Here we demonstrate that intrachromosomal duplications are a key mechanism of accessory chromosome evolution in the F. oxysporum species complex. We identified a single accessory chromosome and show that TR4 mutants that lost this accessory chromosome display significantly reduced virulence on banana plants. Our results provide insight into the evolution of accessory chromosomes in the F. oxysporum species complex, underscore their importance in pathogenicity, and provide new clues for the development of resistant banana plants.

microbiology↗

bioRxiv2023

Why do some fungi want to be sterile? The role of dysfunctional Pro1 in the rice blast fungus

Although sexual reproduction is widespread in eukaryotes, some fungal species can only reproduce asexually. Therefore, loss of sexual reproduction may confer survival advantages under certain conditions in certain species. In the rice blast fungus Pyricularia (Magnaporthe) oryzae, several isolates from the region of origin retain mating ability (female fertility), but most isolates are female sterile. Therefore, it is hypothesized that female fertility was lost during its spread from the origin to the rest of the world, and P. oryzae is an ideal biological model for studying the cause of the evolutionary shift in the reproductive mode. Here, we show that functional mutations of Pro1, a global transcriptional regulator of mating-related genes in filamentous fungi, is one cause of loss of female fertility in this fungus. Employing backcrossing between female-fertile and female-sterile field isolates, we identified the putative genomic region involved in female sterility by comparative genomics between the genomes of F4 female-fertile and -sterile progenies. Further genotyping, linkage, and functional analyses revealed that the functional mutation of Pro1 causes the loss of female fertility. RNA sequencing analysis showed that Pro1 regulates global gene expression, including that of several mating-related genes. The dysfunctional Pro1 did not affect the infection processes, such as conidial germination, appressorium formation, and penetration, but conidial release from conidiophores was increased. Furthermore, various types of mutations in Pro1 were detected in geographically distant P. oryzae, including pandemic isolates of wheat blast fungus. These results provide the first evidence that loss of female fertility may be advantageous to the life cycle of some plant pathogenic fungi. SignificanceMany pathogenic and industrial fungi are thought to have abdicated sexual reproduction, but the mechanisms and biological importance have been a long-standing mystery. Discovering why such fungi lost fertility is important to understand their survival strategies. Here, we revealed the genetic basis of how the rice blast fungus lost female fertility in nature and how this affects the life cycle. This has important implications for understanding evolution of blast pathogens and for developing an effective management strategy to control blast disease before a pandemic. Our findings also provide an additional perspective on advantages of asexual reproduction in some eukaryotes.

microbiology↗