Gene transfers shaped the evolution of de novo NAD+ biosynthesis in eukaryotes

NAD+ is an essential molecule for life, present in each living cell. It can function as an electron carrier or cofactor in redox biochemistry and energetics, and serves as substrate to generate the secondary messenger cyclic ADP ribose and nicotinic acid adenine dinucleotide phosphate. Although de novo NAD+ biosynthesis is essential, different metabolic pathways exist in different eukaryotic clades. The kynurenine pathway starting with tryptophan was most likely present in the last common ancestor of all eukaryotes, and is active in fungi and animals. The aspartate pathway, detected in most photosynthetic eukaryotes, was probably acquired from the cyanobacterial endosymbiont that gave rise to chloroplasts. An evolutionary analysis of enzymes catalyzing de novo NAD+ biosynthesis resulted in evolutionary trees incongruent with established organismal phylogeny, indicating numerous gene transfers. Endosymbiotic gene transfers probably introduced the aspartate pathway into eukaryotes and may have distributed it among different photosynthetic clades. In addition, several horizontal gene transfers substituted eukaryotic genes with bacterial orthologs. Although horizontal gene transfer is accepted as a key mechanism in prokaryotic evolution, it is supposed to be rare in eukaryotic evolution. The essential metabolic pathway of de novo NAD+ biosynthesis in eukaryotes was shaped by numerous gene transfers.Peer reviewedBotan

Calcium Signals from the Vacuole

The vacuole is by far the largest intracellular Ca2+ store in most plant cells. Here, the current knowledge about the molecular mechanisms of vacuolar Ca2+ release and Ca2+ uptake is summarized, and how different vacuolar Ca2+ channels and Ca2+ pumps may contribute to Ca2+ signaling in plant cells is discussed. To provide a phylogenetic perspective, the distribution of potential vacuolar Ca2+ transporters is compared for different clades of photosynthetic eukaryotes. There are several candidates for vacuolar Ca2+ channels that could elicit cytosolic [Ca2+] transients. Typical second messengers, such as InsP3 and cADPR, seem to trigger vacuolar Ca2+ release, but the molecular mechanism of this Ca2+ release still awaits elucidation. Some vacuolar Ca2+ channels have been identified on a molecular level, the voltage-dependent SV/TPC1 channel, and recently two cyclic-nucleotide-gated cation channels. However, their function in Ca2+ signaling still has to be demonstrated. Ca2+ pumps in addition to establishing long-term Ca2+ homeostasis can shape cytosolic [Ca2+] transients by limiting their amplitude and duration, and may thus affect Ca2+ signaling

A Novel Calcium Binding Site in the Slow Vacuolar Cation Channel TPC1 Senses Luminal Calcium Levels[W]

The slow vacuolar channel is the dominant cation channel of the vacuolar membrane and is regulated by cytosolic as well as vacuolar calcium. Here, the vacuolar calcium binding site is characterized at the molecular level, adding to our understanding of calcium signaling in the extracytosolic space

Slow vacular channels from channels from barley mesophyll cells are regulated by 14-3-3 proteins

The conductance of the vacuolar membrane at elevated cytosolic Ca2+ levels is dominated by the slow activating cation selective (SV) channel. At physiological, submicromolar Ca2+ concentrations the SV currents are very small. Only recently has the role of 14-3-3 proteins in the regulation of voltage-gated and Ca2+-activated plasma membrane ion channels been investigated in Drosophila, Xenopus and plants. Here we report the first evidence that plant 14-3-3 proteins are Involved in the down-regulation of ion channels in the vacuolar membrane as well. Using the patch-clamp technique we have demonstrated that 14-3-3 protein drastically reduces the current carried by SV channels, The current decline amounted to 80% and half-maximal reduction was reached within 5 s after 14-3-3-addition to the bath, The voltage sensitivity of the channel was not affected by 14-3-3. A coordinating role for 14-3-3 proteins in the regulation of plasma membrane and tonoplast ion transporters is discussed. (C) 2001 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved

Galdieria_in_Richmond_Mine_FISH

Micrographs of two G. sulphuraria cells detected using Cya1208 rRNA probe in an A-drift biofilm from the Richmond Min

208_Genomes

List of 208 sequenced genomes used to generate protein families and phylogenetic tree