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Asexual thalli originated from sporophytic thalli via apomeiosis in the green seaweed Ulva.

ABSTRACT: Apomixis is an asexual reproduction system without fertilization, which is an important proliferation strategy for plants and algae. Here, we report on the apomeiosis in the green seaweed Ulva prolifera, which has sexual and obligate asexual populations. Genomic PCR of mating type (MT)-locus genes revealed asexual thalli carrying both MT genomes. Observation of the chromosomes during the formation of each type of reproductive cell revealed that cells in asexual thalli performed apomeiosis without chromosome reduction. Moreover, genotyping revealed that laboratory-cultured sporophytic thalli produced not only each type of gametophyte but also diploid thalli carrying the mt^- and mt⁺ genome (mt^± thallus strains). The mt^± thallus strain released diploid biflagellate zoids, with ultrastructure and behavior similar to mt⁺ gametes. Additionally, a transcriptomic analysis revealed that some meiosis-related genes (Mei2L and RAD1) were highly expressed in the quadriflagellate zoosporoids. Our results strongly suggest that asexual thalli originally evolved via apomeiosis in sporophytic thalli.

SUBMITTER: Ichihara K

PROVIDER: S-EPMC6751216 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature

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Asexual thalli originated from sporophytic thalli via apomeiosis in the green seaweed Ulva.

Ichihara Kensuke K Yamazaki Tomokazu T Miyamura Shinichi S Hiraoka Masanori M Kawano Shigeyuki S

Scientific reports 20190918 1

Apomixis is an asexual reproduction system without fertilization, which is an important proliferation strategy for plants and algae. Here, we report on the apomeiosis in the green seaweed Ulva prolifera, which has sexual and obligate asexual populations. Genomic PCR of mating type (MT)-locus genes revealed asexual thalli carrying both MT genomes. Observation of the chromosomes during the formation of each type of reproductive cell revealed that cells in asexual thalli performed apomeiosis withou ...[more]

PMID: 31534182

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Project description:Increased amounts of reactive oxygen species (ROS) have been implicated in many pathological conditions, including cancer. The major machinery that the cell employs to neutralize excess ROS is through the activation of the antioxidant-response element (ARE) that controls the activation of many phase II detoxification enzymes. The transcription factor that recognizes the ARE, Nrf2, can be activated by a variety of small molecules, most of which contain an ?,?-unsaturated carbonyl system. In the pursuit of chemopreventive agents from marine organisms, we built, fractionated, and screened a library of 30 field-collected eukaryotic algae from Florida. An edible green alga, Ulva lactuca, yielded multiple active fractions by ARE-luciferase reporter assay. We isolated three monounsaturated fatty acid (MUFA) derivatives as active components, including a new keto-type C18 fatty acid (1), the corresponding shorter chain C16 acid (2), and an amide derivative (3) of the C18 acid. Their chemical structures were elucidated by NMR and mass spectrometry. All three contain the conjugated enone motif between C7 and C9, which is thought to be responsible for the ARE activity. Subsequent biological studies focused on 1, the most active and abundant ARE activator isolated. C18 acid 1 induced the expression of ARE-regulated cytoprotective genes, including NAD(P)H:quinone oxidoreductase 1, heme oxygenase 1, thioredoxin reductase 1, both subunits of the glutamate-cysteine ligase (catalytic subunit and modifier subunit), and the cystine/glutamate exchange transporter, in IMR-32 human neuroblastoma cells. Its cellular activity requires the presence of Nrf2 and PI3K function, based on RNA interference and pharmacological inhibitor studies, respectively. Treatment with 1 led only to Nrf2 activation, and not the increase in production of NRF2 mRNA. To test its ARE activity and cytoprotective potential in vivo, we treated mice with a single dose of a U. lactuca fraction that was enriched with 1, which showed ARE-activating effects similar to those observed in vitro. This could be owing to this fraction's ability to stabilize Nrf2 through inhibition of Keap1-mediated Nrf2 ubiquitination and the subsequent accumulation and nuclear translocation of Nrf2. The induction of many ARE-driven antioxidant genes in vivo and most prominently in the heart agreed with the commonly recognized cardioprotective properties of MUFAs. A significant increase in Nqo1 transcript levels was also found in other mouse tissues such as the brain, lung, and stomach. Collectively, this study provides new insight into why consumption of dietary seaweed may have health benefits, and the identified compounds add to the list of chemopreventive dietary unsaturated fatty acids.

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Asexual thalli originated from sporophytic thalli via apomeiosis in the green seaweed Ulva.

Publications

Asexual thalli originated from sporophytic thalli via apomeiosis in the green seaweed Ulva.

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