The use of some multiple-sequence alignments in phylogenetic analysis, particularly those that are not very well conserved, requires the elimination of poorly aligned positions and divergent regions, since they may not be homologous or may have been saturated by multiple substitutions. A computerized method that eliminates such positions and at the same time tries to minimize the loss of informative sites is presented here. The method is based on the selection of blocks of positions that fulfill a simple set of requirements with respect to the number of contiguous conserved positions, lack of gaps, and high conservation of flanking positions, making the final alignment more suitable for phylogenetic analysis. To illustrate the efficiency of this method, alignments of 10 mitochondrial proteins from several completely sequenced mitochondrial genomes belonging to diverse eukaryotes were used as examples. The percentages of removed positions were higher in the most divergent alignments. After removing divergent segments, the amino acid composition of the different sequences was more uniform, and pairwise distances became much smaller. Phylogenetic trees show that topologies can be different after removing conserved blocks, particularly when there are several poorly resolved nodes. Strong support was found for the grouping of animals and fungi but not for the position of more basal eukaryotes. The use of a computerized method such as the one presented here reduces to a certain extent the necessity of manually editing multiple alignments, makes the automation of phylogenetic analysis of large data sets feasible, and facilitates the reproduction of the final alignment by other researchers.

/pdf/selection-of-conserved-blocks-from-multiple-alignments-for-i0qfazjwh5.pdf

Selection of Conserved Blocks from Multiple Alignments for Their Use in Phylogenetic Analysis

The flowering plant Arabidopsis thaliana is an important model system for identifying genes and determining their functions. Here we report the analysis of the genomic sequence of Arabidopsis. The sequenced regions cover 115.4 megabases of the 125-megabase genome and extend into centromeric regions. The evolution of Arabidopsis involved a whole-genome duplication, followed by subsequent gene loss and extensive local gene duplications, giving rise to a dynamic genome enriched by lateral gene transfer from a cyanobacterial-like ancestor of the plastid. The genome contains 25,498 genes encoding proteins from 11,000 families, similar to the functional diversity of Drosophila and Caenorhabditis elegans--the other sequenced multicellular eukaryotes. Arabidopsis has many families of new proteins but also lacks several common protein families, indicating that the sets of common proteins have undergone differential expansion and contraction in the three multicellular eukaryotes. This is the first complete genome sequence of a plant and provides the foundations for more comprehensive comparison of conserved processes in all eukaryotes, identifying a wide range of plant-specific gene functions and establishing rapid systematic ways to identify genes for crop improvement.

/pdf/analysis-of-the-genome-sequence-of-the-flowering-plant-3vizsb52m2.pdf

Analysis of the genome sequence of the flowering plant Arabidopsis thaliana.

Low temperature, drought, and high salinity are common stress conditions that adversely affect plant growth and crop production. The cellular and molecular responses of plants to environmental stress have been studied intensively ([Thomashow, 1999][1]; [Hasegawa et al., 2000][2]). Understanding the

/pdf/cell-signaling-during-cold-drought-and-salt-stress-2v6yqzaitr.pdf

Cell Signaling during Cold, Drought, and Salt Stress

Summary
The diets of over two-thirds of the world's population lack one or more essential mineral elements. This can be remedied through dietary diversification, mineral supplementation, food fortification, or increasing the concentrations and/or bioavailability of mineral elements in produce (biofortification). This article reviews aspects of soil science, plant physiology and genetics underpinning crop biofortification strategies, as well as agronomic and genetic approaches currently taken to biofortify food crops with the mineral elements most commonly lacking in human diets: iron (Fe), zinc (Zn), copper (Cu), calcium (Ca), magnesium (Mg), iodine (I) and selenium (Se). Two complementary approaches have been successfully adopted to increase the concentrations of bioavailable mineral elements in food crops. First, agronomic approaches optimizing the application of mineral fertilizers and/or improving the solubilization and mobilization of mineral elements in the soil have been implemented. Secondly, crops have been developed with: increased abilities to acquire mineral elements and accumulate them in edible tissues; increased concentrations of ‘promoter’ substances, such as ascorbate, β-carotene and cysteine-rich polypeptides which stimulate the absorption of essential mineral elements by the gut; and reduced concentrations of ‘antinutrients’, such as oxalate, polyphenolics or phytate, which interfere with their absorption. These approaches are addressing mineral malnutrition in humans globally.

/pdf/biofortification-of-crops-with-seven-mineral-elements-often-3g2xc3trnk.pdf

Biofortification of crops with seven mineral elements often lacking in human diets--iron, zinc, copper, calcium, magnesium, selenium and iodine.

We have developed the web application GeSeq (https://chlorobox.mpimp-golm.mpg.de/geseq.html) for the rapid and accurate annotation of organellar genome sequences, in particular chloroplast genomes. In contrast to existing tools, GeSeq combines batch processing with a fully customizable reference sequence selection of organellar genome records from NCBI and/or references uploaded by the user. For the annotation of chloroplast genomes, the application additionally provides an integrated database of manually curated reference sequences. GeSeq identifies genes or other feature-encoding regions by BLAT-based homology searches and additionally, by profile HMM searches for protein and rRNA coding genes and two de novo predictors for tRNA genes. These unique features enable the user to conveniently compare the annotations of different state-of-the-art methods, thus supporting high-quality annotations. The main output of GeSeq is a GenBank file that usually requires only little curation and is instantly visualized by OGDRAW. GeSeq also offers a variety of optional additional outputs that facilitate downstream analyzes, for example comparative genomic or phylogenetic studies.

GeSeq - versatile and accurate annotation of organelle genomes.

We have determined the complete sequence of the mitochondrial DNA in the model plant species Arabidopsis thaliana, affording access to the first of its three genomes. The 366,924 nucleotides code for 57 identified genes, which cover only 10% of the genome. Introns in these genes add about 8%, open reading frames larger than 100 amino acids represent 10% of the genome, duplications account for 7%, remnants of retrotransposons of nuclear origin contribute 4% and integrated plastid sequences amount to 1%-leaving 60% of the genome unaccounted for. With the significant contribution of duplications, imported foreign DNA and the extensive background of apparently functionless sequences, the mosaic structure of the Arabidopsis thaliana mitochondrial genome features many aspects of size-relaxed nuclear genomes.

The mitochondrial genome of Arabidopsis thaliana contains 57 genes in 366,924 nucleotides

On the basis of the sequence of the mitochondrial genome in the flowering plant Arabidopsis thaliana, RNA editing events were systematically investigated in the respective RNA population. A total of 456 C to U, but no U to C, conversions were identified exclusively in mRNAs, 441 in ORFs, 8 in introns, and 7 in leader and trailer sequences. No RNA editing was seen in any of the rRNAs or in several tRNAs investigated for potential mismatch corrections. RNA editing affects individual coding regions with frequencies varying between 0 and 18.9% of the codons. The predominance of RNA editing events in the first two codon positions is not related to translational decoding, because it is not correlated with codon usage. As a general effect, RNA editing increases the hydrophobicity of the coded mitochondrial proteins. Concerning the selection of RNA editing sites, little significant nucleotide preference is observed in their vicinity in comparison to unedited C residues. This sequence bias is, per se, not sufficient to specify individual C nucleotides in the total RNA population in Arabidopsis mitochondria.

https://www.pnas.org/content/pnas/96/26/15324.full.pdf

RNA editing in Arabidopsis mitochondria effects 441 C to U changes in ORFs

Comparative sequence analysis of genomic and complementary DNA clones from several mitochondrial genes in the higher plant Oenothera revealed nucleotide sequence divergences between the genomic and the messenger RNA-derived sequences. These sequence alterations could be most easily explained by specific post-transcriptional nucleotide modifications. Most of the nucleotide exchanges in coding regions lead to altered codons in the mRNA that specify amino acids better conserved in evolution than those encoded by the genomic DNA. Several instances show that the genomic arginine codon CGG is edited in the mRNA to the tryptophan codon TGG in amino acid positions that are highly conserved as tryptophan in the homologous proteins of other species. This editing suggests that the standard genetic code is used in plant mitochondria and resolves the frequent coincidence of CGG codons and tryptophan in different plant species. The apparently frequent and non-species-specific equivalency of CGG and TGG codons in particular suggests that RNA editing is a common feature of all higher plant mitochondria.

https://science.sciencemag.org/content/sci/246/4937/1632.full.pdf

RNA Editing in Plant Mitochondria

RNA editing alters the identity of nucleotides in RNA molecules such that the information for a protein in the mRNA differs from the prediction of the genomic DNA. In chloroplasts and mitochondria of flowering plants, RNA editing changes C nucleotides to U nucleotides; in ferns and mosses, it also changes U to C. The approximately 500 editing sites in mitochondria and 40 editing sites in plastids of flowering plants are individually addressed by specific proteins, genes for which are amplified in plant species with organellar RNA editing. These proteins contain repeat elements that bind to cognate RNA sequence motifs just 5′ to the edited nucleotide. In flowering plants, the site-specific proteins interact selectively with individual members of a different, smaller family of proteins. These latter proteins may be connectors between the site-specific proteins and the as yet unknown deaminating enzymatic activity.

RNA editing in plants and its evolution.

RNA editing in plastids and mitochondria of flowering plants changes hundreds of selected cytidines to uridines, mostly in coding regions of mRNAs. Specific sequences around the editing sites are presumably recognized by up to 200 pentatricopeptide repeat (PPR) proteins. The here identified family of multiple organellar RNA editing factor (MORF) proteins provides additional components of the RNA editing machinery in both plant organelles. Two MORF proteins are required for editing in plastids; at least two are essential for editing in mitochondria. The loss of a MORF protein abolishes or lowers editing at multiple sites, many of which are addressed individually by PPR proteins. In plastids, both MORF proteins are required for complete editing at almost all sites, suggesting a heterodimeric complex. In yeast two-hybrid and pull-down assays, MORF proteins can connect to form hetero- and homodimers. Furthermore, MORF proteins interact selectively with PPR proteins, establishing a more complex editosome in plant organelles than previously thought.

https://www.pnas.org/content/pnas/109/13/5104.full.pdf

Axel Brennicke

Papers

The mitochondrial genome of Arabidopsis thaliana contains 57 genes in 366,924 nucleotides

RNA editing in Arabidopsis mitochondria effects 441 C to U changes in ORFs

RNA Editing in Plant Mitochondria

RNA editing in plants and its evolution.

Multiple organellar RNA editing factor (MORF) family proteins are required for RNA editing in mitochondria and plastids of plants