A unicellular algal virus, Emiliania huxleyi virus 86, exploits an animal-like infection strategy.

Emiliania huxleyi virus 86 (EhV-86) belongs to the family Phycodnaviridae, a group of viruses that infect a wide range of freshwater and marine eukaryotic algae. Phycodnaviridae is one of the five families that belong to a large and phylogenetically diverse group of viruses known as nucleocytoplasmic large dsDNA viruses (NCLDVs). To date, our understanding of algal NCLDV entry is based on the entry mechanisms of members of the genera Chlorovirus and Phaeovirus, both of which consist of non-enveloped viruses that 'inject' their genome into their host via a viral inner-membrane host plasma membrane fusion mechanism, leaving an extracellular viral capsid. Using a combination of confocal and electron microscopy, this study demonstrated for the first time that EhV-86 differs from its algal virus counterparts in two fundamental areas. Firstly, its capsid is enveloped by a lipid membrane, and secondly, EhV-86 enters its host via either an endocytotic or an envelope fusion mechanism in which an intact nucleoprotein core still encapsulated by its capsid is seen in the host cytoplasm. Real-time fluorescence microscopy showed that viral internalization and virion breakdown took place within the host on a timescale of seconds. At around 4.5 h post-infection, virus progeny were released via a budding mechanism during which EhV-86 virions became enveloped with host plasma membrane. EhV-86 therefore appears to have an infection mechanism different from that employed by other algal NCLDVs, with entry and exit strategies showing a greater analogy to animal-like NCLDVs.

Calcification and inorganic carbon acquisition in coccolithophores.

A number of species of coccolithophorid phytoplankton precipitate calcite inside intracellular vesicles (coccolith vesicles). They can form vast blooms under certain conditions, and account for major fluxes of inorganic carbon (Ci) to the ocean floor. The functions of calcification have been debated for many years, and a role in carbon acquisition has been proposed by several workers. The precipitation of calcite from HCO3- involves the production of protons that can potentially be used to facilitate the use of external HCO3- as a photosynthetic substrate. For this function to be feasible, certain criteria must be met. HCO3- (rather than CO32-) should be the external substrate for calcification, photosynthesis should be facilitated by HCO3- in calcifying cells when CO2 availability is limiting, and the transport of Ci and Ca2+ to the site of calcification should be energetically and kinetically feasible. Considerable evidence exists for HCO3- as the substrate for calcification in coccolithophores. However, evidence for a direct role for calcification in supply of Ci for photosynthesis is less clear. The environmental factors that regulate calcification are still uncertain but appear to be related as much to the availability of nutrients as CO2. Transport of Ci to the intracellular site of calcification and removal of H+ from the coccolith vesicle appear to present few energetic or kinetic constraints. However, the large sustained transcellular fluxes of Ca2+ required for calcification probably occur via a pathway that does not involve diffusion across the cytoplasm.

Spatiotemporal patterning of reactive oxygen production and Ca(2+) wave propagation in fucus rhizoid cells.

Both Ca(2+) and reactive oxygen species (ROS) play critical signaling roles in plant responses to biotic and abiotic stress. However, the positioning of Ca(2+) and ROS (in particular H(2)O(2)) after a stress stimulus and their subcellular interactions are poorly understood. Moreover, although information can be encoded in different patterns of cellular Ca(2+) signals, little is known about the subcellular spatiotemporal patterns of ROS production or their significance for downstream responses. Here, we show that ROS production in response to hyperosmotic stress in embryonic cells of the alga Fucus serratus consists of two distinct components. The first ROS component coincides closely with the origin of a Ca(2+) wave in the peripheral cytosol at the growing cell apex, has an extracellular origin, and is necessary for the Ca(2+) wave. Patch-clamp experiments show that a nonselective cation channel is stimulated by H(2)O(2) and may underlie the initial cytosolic Ca(2+) increase. Thus, the spatiotemporal pattern of the Ca(2+) wave is determined by peripheral ROS production. The second, later ROS component localizes to the mitochondria and is a direct consequence of the Ca(2+) wave. The first component, but not the second, is required for short-term adaptation to hyperosmotic stress. Our results highlight the role of ROS in the patterning of a Ca(2+) signal in addition to its function in regulating cell wall strength in the Fucus embryo.