Gene expression analysis of “green tide” alga Ulva prolifera (Chlorophyta) in China

Molecular Response of Ulva prolifera to Short-Term High Light Stress Revealed by a Multi-Omics Approach

The main algal species of Ulva prolifera green tide in the coastal areas of China are four species, but after reaching the coast of Qingdao, U. prolifera becomes the dominant species, where the light intensity is one of the most important influencing factors. In order to explore the effects of short-term high light stress on the internal molecular level of cells and its coping mechanism, the transcriptome, proteome, metabolome, and lipid data of U. prolifera were collected. The algae were cultivated in high light environment conditions (400 μmol·m−2·s−1) for 12 h and measured, and the data with greater relative difference (p < 0.05) were selected, then analyzed with the KEGG pathway. The results showed that the high light stress inhibited the assimilation of U. prolifera, destroyed the cell structure, and arrested its growth and development. Cells entered the emergency defense state, the TCA cycle was weakened, and the energy consumption processes such as DNA activation, RNA transcription, protein synthesis and degradation, and lipid alienation were inhibited. A gradual increase in the proportion of the C4 pathway was recorded. This study showed that U. prolifera can reduce the reactive oxygen species produced by high light stress, inhibit respiration, and reduce the generation of NADPH. At the same time, the C3 pathway began to change to the C4 pathway which consumed more energy. Moreover, this research provides the basis for the study of algae coping with high light stress.

Molecular genetic diversity of seaweeds morphologically related to Ulva rigida at three sites along the French Atlantic coast

Foliose species of the genus Ulva are notoriously difficult to identify due to their variable morphological characteristics and high phenotypic plasticity. We reassessed the taxonomic status of several distromatic foliose Ulva spp., morphologically related to Ulva rigida, using DNA barcoding with the chloroplastic tufA and rbcL (for a subset of taxa) genes for 339 selected attached Ulva specimens collected from three intertidal rocky sites. Two of the collection sites were in Brittany and one site was in Vendée, along the Atlantic coast of France. Molecular analyses included several museum specimens and the holotype of Ulva armoricana Dion, Reviers & Coat. We identified five different tufA haplotypes using a combination of phylogenetic analysis, with the support of several recently sequenced holotypes and lectotypes, and a species delimitation method based on hierarchical clustering. Four haplotypes were supported by validly named species: Ulva australis Areschoug, Ulva fenestrata Postels & Ruprecht, Ulva lacinulata (Kützing) Wittrock and U. rigida C. Agardh. The later was additionally investigated using rbcL. The fifth haplotype represented exact sequence matches to an unnamed species from European Atlantic coasts. Our results support: (1) the synonymy of both U. rigida sensu Bliding non C. Agardh and U. armoricana with U. lacinulata. This finding is based on current genetic analysis of tufA from the U. armoricana holotype and recent molecular characterization of the lectotype of U. laetevirens, which is synonymous to U. australis, (2) the presence of U. australis as a misidentified introduced species in Brittany, and (3) the presence of U. fenestrata and U. rigida in southern Brittany. The taxonomic history of each species is discussed, highlighting issues within distromatic foliose taxa of the genus Ulva and the need to genetically characterize all its available type specimens.

Saturating light and not increased carbon dioxide under ocean acidification drives photosynthesis and growth in Ulva rigida (Chlorophyta)

Carbon physiology of a genetically identified Ulva rigida was investigated under different CO2(aq) and light levels. The study was designed to answer whether (1) light or exogenous inorganic carbon (Ci) pool is driving growth; and (2) elevated CO2(aq) concentration under ocean acidification (OA) will downregulate CAext-mediated [Formula: see text] dehydration and alter the stable carbon isotope (δ (13)C) signatures toward more CO2 use to support higher growth rate. At pHT 9.0 where CO2(aq) is <1 μmol L(-1), inhibition of the known [Formula: see text] use mechanisms, that is, direct [Formula: see text] uptake through the AE port and CAext-mediated [Formula: see text] dehydration decreased net photosynthesis (NPS) by only 56-83%, leaving the carbon uptake mechanism for the remaining 17-44% of the NPS unaccounted. An in silico search for carbon-concentrating mechanism elements in expressed sequence tag libraries of Ulva found putative light-dependent [Formula: see text] transporters to which the remaining NPS can be attributed. The shift in δ (13)C signatures from -22‰ toward -10‰ under saturating light but not under elevated CO2(aq) suggest preference and substantial [Formula: see text] use to support photosynthesis and growth. U. rigida is Ci saturated, and growth was primarily controlled by light. Therefore, increased levels of CO2(aq) predicted for the future will not, in isolation, stimulate Ulva blooms.