Kajita Tadashi




Researcher Number(JSPS Kakenhi)


Current Affiliation Organization 【 display / non-display

  • Duty   University of the Ryukyus   Tropical Biosphere Research Center   Professor  

External Career 【 display / non-display

  • 2015.05

    University of the Ryukyus, Tropical Biosphere Research Center, Professor  

Research Interests 【 display / non-display

  • 分子系統学

  • 保全生物学

  • マングローブ

  • マメ科

  • Sea-dispersal

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Published Papers 【 display / non-display

  • Massive rhizobial genomic variation associated with partner quality in Lotus-Mesorhizobium symbiosis.

    Bamba M, Aoki S, Kajita T, Setoguchi H, Watano Y, Sato S, Tsuchimatsu T

    FEMS microbiology ecology   96 ( 12 )   2020.10 [ Peer Review Accepted ]

    Type of publication: Research paper (scientific journal)

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    Variation in partner quality is commonly observed in diverse cooperative relationships, despite the theoretical prediction that selection favoring high-quality partners should eliminate such variation. Here, we investigated how genetic variation in partner quality could be maintained in the nitrogen-fixing mutualism between Lotus japonicus and Mesorhizobium bacteria. We reconstructed de novo assembled full-genome sequences from nine rhizobial symbionts, finding massive variation in the core genome and the similar symbiotic islands, indicating recent horizontal gene transfer (HGT) of the symbiosis islands into diverse Mesorhizobium lineages. A cross-inoculation experiment using 9 sequenced rhizobial symbionts and 15 L. japonicus accessions revealed extensive quality variation represented by plant growth phenotypes, including genotype-by-genotype interactions. Variation in quality was not associated with the presence/absence variation in known symbiosis-related genes in the symbiosis island; rather, it showed significant correlation with the core genome variation. Given the recurrent HGT of the symbiosis islands into diverse Mesorhizobium strains, local Mesorhizobium communities could serve as a major source of variation for core genomes, which might prevent variation in partner quality from fixing, even in the presence of selection favoring high-quality partners. These findings highlight the novel role of HGT of symbiosis islands in maintaining partner quality variation in the legume-rhizobia symbiosis.

  • Genetic structures across a biogeographical barrier reflect dispersal potential of four Southeast Asian mangrove plant species

    Wee A.K.S.

    Journal of Biogeography ( Journal of Biogeography )  47 ( 6 ) 1258 - 1271   2020.06 [ Peer Review Accepted ]

    Type of publication: Research paper (scientific journal)

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    Aim Biogeographical barriers restrict the movement of individuals, resulting in population divergence, genetic differentiation, endemism and speciation. Yet, some barriers demonstrate unequal effect across species depending on species dispersal, which manifests in varying genetic structure. We test the hypotheses that the genetic structure of four coastal mangrove species would reflect differences in dispersal potential across the Malay Peninsula, a major biogeographical barrier in the Indo-West Pacific region.Location East and west coasts of the Malay Peninsula.Taxon Mangrove trees Avicennia alba, Sonneratia alba, Bruguiera gymnorhiza and Rhizophora mucronata.Methods For each species, we characterized genetic structure and gene flow using 7-12 species-specific nuclear microsatellite markers. We tested for east-west genetic differentiation across the peninsula, a stepping-stone migration pattern, and assessed the proportion of recent dispersal and direction of historical migration along the Malacca Strait.Results Significant east-west genetic differentiation across the peninsula was observed in A. alba, S. alba and B. gymnorhiza, and the effect was most pronounced for the two species with lower dispersal potential (A. alba, S. alba). In contrast, the two species with higher dispersal potential (B. gymnorhiza and R. mucronata) exhibited much higher proportion of recent inter-population migration along the Malacca Strait. The signature of historical colonization from refugia in the Andaman Sea (north-to-south migration along the Malacca Strait) predominated for A. alba and S. alba. Historical south-north migration predominated for R. mucronata and B. gymnorhiza.Main conclusions This study is the first to implicate dispersal potential as a causal factor of varying mangrove species genetic structure across a biogeographical barrier. The Malay Peninsula functions as a filter to gene flow rather than a barrier. The genetic structure in mangrove species with a higher dispersal potential is more congruent with contemporary gene flow while that of species with a lower dispersal potential reflects historical processes. Our findings hint at the role of dispersal potential as a predictor of gene flow in mangroves.

  • Niche conservatism promotes speciation in cycads: the case of Dioon merolae (Zamiaceae) in Mexico.

    Gutiérrez-Ortega JS, Salinas-Rodríguez MM, Ito T, Pérez-Farrera MA, Vovides AP, Martínez JF, Molina-Freaner F, Hernández-López A, Kawaguchi L, Nagano AJ, Kajita T, Watano Y, Tsuchimatsu T, Takahashi Y, Murakami M

    The New phytologist ( New Phytologist )  227 ( 6 ) 1872 - 1884   2020.05 [ Peer Review Accepted ]

    Type of publication: Research paper (scientific journal)

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    Niche conservatism is the tendency of lineages to retain the same niche as their ancestors. It constrains biological groups and prevents ecological divergence. However, theory predicts that niche conservatism can hinder gene flow, strengthen drift and increase local adaptation: does it mean that it also can facilitate speciation? Why does this happen? We aim to answer these questions. We examined the variation of chloroplast DNA, genome-wide single nucleotide polymorphisms, morphological traits and environmental variables across the Dioon merolae cycad populations. We tested geographical structure, scenarios of demographic history, and niche conservatism between population groups. Lineage divergence is associated with the presence of a geographical barrier consisting of unsuitable habitats for cycads. There is a clear genetic and morphological distinction between the geographical groups, suggesting allopatric divergence. However, even in contrasting available environmental conditions, groups retain their ancestral niche, supporting niche conservatism. Niche conservatism is a process that can promote speciation. In D. merolae, lineage divergence occurred because unsuitable habitats represented a barrier against gene flow, incurring populations to experience isolated demographic histories and disparate environmental conditions. This study explains why cycads, despite their ancient lineage origin and biological stasis, have been able to diversify into modern ecosystems worldwide.

  • The complete chloroplast genome of a hemiparasitic plant Santalum boninense (Santalaceae), endemic to the Bonin (Ogasawara) Islands

    Nishimura Akihiro, Kajita Tadashi, Takayama Koji

    MITOCHONDRIAL DNA PART B-RESOURCES ( TAYLOR & FRANCIS LTD )  5 ( 2 ) 1386 - 1387   2020.04 [ Peer Review Accepted ]

    Type of publication: Research paper (scientific journal)

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    The complete chloroplast genome sequence of a hemiparasitic plant Santalum boninense (Santalaceae) was determined and described in this study. The chloroplast genome was 144,263 bp in length, consisting of a large single-copy region (83,912 bp), a small single-copy region (11,349 bp), and inverted repeats (24,501 bp). The chloroplast genome contained 124 genes including 72 protein-coding genes, 35 tRNA genes, eight rRNA genes, and nine pseudogenes. All the ndh genes and infA gene were found to lose function by gene loss or pseudogenization. GC content of the whole chloroplast genome was 38.0%.

  • Two new species of <i>Ardisia</i> subgenus <i>Tetrardisia</i> (Primulaceae-Myrsinoideae) from Borneo.

    Julius A, Kajita T, Utteridge TMA

    PhytoKeys ( PENSOFT PUBLISHERS )  145 ( 145 ) 139 - 148   2020 [ Peer Review Accepted ]

    Type of publication: Research paper (scientific journal)

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    Ardisia argentiana and A. nagaensis from subgenus Tetrardisia are herein described and illustrated as new species. They are endemic to Borneo and the Indonesian province of Central Kalimantan and to the Malaysian state of Sarawak, respectively. Ardisia argentiana is unique in its linear-oblong leaves, with a long, acuminate-caudate apex, and finely serrulate margins, while A. nagaensis can be easily recognized by its elliptic-lanceolate leaves.

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