Transcriptome Profiling in the Marine Red Alga Neopyropia yezoensis Under Light/Dark Cycle

Diel variations in nutrient physiology among commercially important eucheumatoids Kappaphycus alvarezii, K. striatus and Eucheuma denticulatum

MAIN CONCLUSION

Eucheumatoids exhibited significant day and night nutrient uptake, with NH4+ increasing linearly, NO3- following Michaelis-Menten kinetics, higher internal NH4+, NO2-, PO4-3 at night, and peak nitrate reductase activity during day. Nutrient physiology of aquatic phototrophs is mostly measured during daytime or experimentally under saturating irradiance with the assumption that nutrient uptake is tightly coupled with photosynthetic activities. At night or under dark condition, when photosynthesis ceases, little is known on the nutrient physiology of these macrophytes. Here, we examined the nutrient uptake of commercially important eucheumatoids Kappaphycus alvarezii, K. striatus, and Eucheuma denticulatum during night and daytime, considering conditions that extend beyond just the presence or absence of light. The NH4+ and NO3- uptake of the three eucheumatoid species were higher during the day (53.4-58.2% of the total TIN absorbed), although nighttime uptake (41.8-46.6% of the total TIN absorbed) also contributed significantly to the overall uptake rates. For both night and daytime, the NH4+ uptake of the three eucheumatoid species increased linearly with the substrate concentration while NO3- uptake followed the Michaelis-Menten saturation kinetics. Higher Vmax were observed for K. striatus (5.670 ± 0.474 µmol h-1 g-1 DW) and E. denticulatum (8.058 ± 1.632 µmol h-1 g-1 DW) during nighttime, while nighttime Km values of the three species (13.028-32.387 µM) were higher compared to their daytime values (6.397-9.238 µM). Regardless of night- or day-sampling time, the nutrient (NH4+, NO3-, NO2- and PO4-3) concentration in the seaweeds' internal pools were higher than their concentrations in the surrounding seawater, highlighting their capacities to store inorganic nutrients. Higher amounts of NH4+, NO2- and PO4-3 in the seaweeds' internal pools were observed during nighttime while NO3- in the internal pools were similar at both periods. Lastly, the three eucheumatoid species exhibited higher nitrate reductase activities (NRAs) during the day. Our study showed that algal nutrient uptake and nitrogen metabolism are independent of light and photosynthesis. Understanding the influence of night and daytime in nutrient uptake can provide insights in the sustainable nutrient management for commercial crop production and/or in incorporating eucheumatoids in an integrated multi-trophic aquaculture (IMTA) system. In terms of accounting for the bioremediation potentials of the above species, it is important to measure both nighttime and daytime nutrient uptakes.

Development of Chromatin Immunoprecipitation for the Analysis of Histone Modifications in Red Macroalga Neopyropia yezoensis (Rhodophyta)

Epigenetic regulation by histone modification can activate or repress transcription through changes in chromatin dynamics and regulates development and the response to environmental signals in both animals and plants. Chromatin immunoprecipitation (ChIP) is an indispensable tool to identify histones with specific post-translational modifications. The lack of a ChIP technique for macroalgae has hindered understanding of the role of histone modification in the expression of genes in this organism. In this study, a ChIP method with several modifications, based on existing protocols for plant cells, has been developed for the red macroalga, Neopyropia yezoensis, that consists of a heterogeneous alternation of macroscopic leaf-like gametophytes and microscopic filamentous sporophytes. ChIP method coupled with qPCR enables the identification of a histone mark in generation-specific genes from N. yezoensis. The results indicate that acetylation of histone H3 at lysine 9 in the 5' flanking and coding regions from generation-specific genes was maintained at relatively high levels, even in generation-repressed gene expression. The use of this ChIP method will contribute significantly to identify the epigenetic regulatory mechanisms through histone modifications that control a variety of biological processes in red macroalgae.

The role of plant hormones on the reproductive success of red and brown algae

Seaweeds or macroalgae are important primary producers that serve as a habitat for functioning ecosystems. A sustainable production of macroalgae has been maintained by a diverse range of life cycles. Reproduction is the most dynamic change to occur during its life cycle, and it is a key developmental event to ensure the species' survival. There is gradually accumulating evidence that plant hormones, such as abscisic acid and auxin, have a role on the sporogenesis of brown alga (Saccharina japonica). Recent studies reported that 1-aminocylopropane-1-carboxylic acid, an ethylene precursor, regulates sexual reproduction in red alga (Neopyropia yezoensis) independently from ethylene. In addition, these macroalgae have an enhanced tolerance against abiotic and biotic stresses during reproduction to protect their gametes and spores. Herein, we reviewed the current understanding on the regulatory mechanisms of red and brown algae on their transition from vegetative to reproductive phase.