Dataset Information

Primitive Extracellular Lipid Components on the Surface of the Charophytic Alga Klebsormidium flaccidum and Their Possible Biosynthetic Pathways as Deduced from the Genome Sequence.

ABSTRACT: Klebsormidium flaccidum is a charophytic alga living in terrestrial and semiaquatic environments. K. flaccidum grows in various habitats, such as low-temperature areas and under desiccated conditions, because of its ability to tolerate harsh environments. Wax and cuticle polymers that contribute to the cuticle layer of plants are important for the survival of land plants, as they protect against those harsh environmental conditions and were probably critical for the transition from aquatic microorganism to land plants. Bryophytes, non-vascular land plants, have similar, but simpler, extracellular waxes and polyester backbones than those of vascular plants. The presence of waxes in terrestrial algae, especially in charophytes, which are the closest algae to land plants, could provide clues in elucidating the mechanism of land colonization by plants. Here, we compared genes involved in the lipid biosynthetic pathways of Arabidopsis thaliana to the K. flaccidum and the Chlamydomonas reinhardtii genomes, and identified wax-related genes in both algae. A simple and easy extraction method was developed for the recovery of the surface lipids from K. flaccidum and C. reinhardtii. Although these algae have wax components, their surface lipids were largely different from those of land plants. We also investigated aliphatic substances in the cell wall fraction of K. flaccidum and C. reinhardtii. Many of the fatty acids were determined to be lipophilic monomers in K. flaccidum, and a Fourier transform infrared spectroscopic analysis revealed that their possible binding mode was distinct from that of A. thaliana. Thus, we propose that K. flaccidum has a cuticle-like hydrophobic layer composed of lipids and glycoproteins, with a different composition from the cutin polymer typically found in land plant cuticles.

SUBMITTER: Kondo S

PROVIDER: S-EPMC4927632 | biostudies-literature | 2016

REPOSITORIES: biostudies-literature

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Primitive Extracellular Lipid Components on the Surface of the Charophytic Alga Klebsormidium flaccidum and Their Possible Biosynthetic Pathways as Deduced from the Genome Sequence.

Kondo Satoshi S Hori Koichi K Sasaki-Sekimoto Yuko Y Kobayashi Atsuko A Kato Tsubasa T Yuno-Ohta Naoko N Nobusawa Takashi T Ohtaka Kinuka K Shimojima Mie M Ohta Hiroyuki H

Frontiers in plant science 20160630

Klebsormidium flaccidum is a charophytic alga living in terrestrial and semiaquatic environments. K. flaccidum grows in various habitats, such as low-temperature areas and under desiccated conditions, because of its ability to tolerate harsh environments. Wax and cuticle polymers that contribute to the cuticle layer of plants are important for the survival of land plants, as they protect against those harsh environmental conditions and were probably critical for the transition from aquatic micro ...[more]

PMID: 27446179

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Project description:Adaptation strategies in freezing resistance were investigated in Klebsormidium crenulatum, an early branching streptophyte green alga related to higher plants. Klebsormidium grows naturally in unfavorable environments like alpine biological soil crusts, exposed to desiccation, high irradiation and cold stress. Here, chilling and freezing induced alterations of the ultrastructure were investigated. Control samples (kept at 20°C) were compared to chilled (4°C) as well as extracellularly frozen algae (-2 and -4°C). A software-controlled laboratory freezer (AFU, automatic freezing unit) was used for algal exposure to various temperatures and freezing was manually induced. Samples were then high pressure frozen and cryo-substituted for electron microscopy. Control cells had a similar appearance in size and ultrastructure as previously reported. While chilling stressed algae only showed minor ultrastructural alterations, such as small inward facing cell wall plugs and minor alterations of organelles, drastic changes of the cell wall and in organelle distribution were found in extracellularly frozen samples (-2°C and -4°C). In frozen samples, the cytoplasm was not retracted from the cell wall, but extensive three-dimensional cell wall layers were formed, most prominently in the corners of the cells, as determined by FIB-SEM and TEM tomography. Similar alterations/adaptations of the cell wall were not reported or visualized in Klebsormidium before, neither in controls, nor during other stress scenarios. This indicates that the cell wall is reinforced by these additional wall layers during freezing stress. Cells allowed to recover from freezing stress (-2°C) for 5 h at 20°C lost these additional cell wall layers, suggesting their dynamic formation. The composition of these cell wall reinforcement areas was investigated by immuno-TEM. In addition, alterations of structure and distribution of mitochondria, dictyosomes and a drastically increased endoplasmic reticulum were observed in frozen cells by TEM and TEM tomography. Measurements of the photosynthetic oxygen production showed an acclimation of Klebsormidium to chilling stress, which correlates with our findings on ultrastructural alterations of morphology and distribution of organelles. The cell wall reinforcement areas, together with the observed changes in organelle structure and distribution, are likely to contribute to maintenance of an undisturbed cell physiology and to adaptation to chilling and freezing stress.

Project description:BACKGROUND:Water loss has significant effects on physiological performance and survival rates of algae. However, despite the prominent presence of aeroterrestrial algae in terrestrial habitats, hardly anything is known about the molecular events that allow aeroterrestrial algae to survive harsh environmental conditions. We analyzed the transcriptome and physiology of a strain of the alpine aeroterrestrial alga Klebsormidium crenulatum under control and strong desiccation-stress conditions. PRINCIPAL FINDINGS:For comparison we first established a reference transcriptome. The high-coverage reference transcriptome includes about 24,183 sequences (1.5 million reads, 636 million bases). The reference transcriptome encodes for all major pathways (energy, carbohydrates, lipids, amino acids, sugars), nearly all deduced pathways are complete or missing only a few transcripts. Upon strong desiccation, more than 7000 transcripts showed changes in their expression levels. Most of the highest up-regulated transcripts do not show similarity to known viridiplant proteins, suggesting the existence of some genus- or species-specific responses to desiccation. In addition, we observed the up-regulation of many transcripts involved in desiccation tolerance in plants (e.g. proteins similar to those that are abundant in late embryogenesis (LEA), or proteins involved in early response to desiccation ERD), and enzymes involved in the biosynthesis of the raffinose family of oligosaccharides (RFO) known to act as osmolytes). Major physiological shifts are the up-regulation of transcripts for photosynthesis, energy production, and reactive oxygen species (ROS) metabolism, which is supported by elevated cellular glutathione content as revealed by immunoelectron microscopy as well as an increase in total antiradical power. However, the effective quantum yield of Photosystem II and CO2 fixation decreased sharply under the applied desiccation stress. In contrast, transcripts for cell integrative functions such as cell division, DNA replication, cofactor biosynthesis, and amino acid biosynthesis were down-regulated. SIGNIFICANCE:This is the first study investigating the desiccation transcriptome of a streptophyte green alga. Our results indicate that the cellular response is similar to embryophytes, suggesting that embryophytes inherited a basic cellular desiccation tolerance from their streptophyte predecessors.

Dataset Information

Primitive Extracellular Lipid Components on the Surface of the Charophytic Alga Klebsormidium flaccidum and Their Possible Biosynthetic Pathways as Deduced from the Genome Sequence.

Publications

Primitive Extracellular Lipid Components on the Surface of the Charophytic Alga Klebsormidium flaccidum and Their Possible Biosynthetic Pathways as Deduced from the Genome Sequence.

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