Genomics and Evolution of Cellular Organelles

Abstract

The structure, functions, and evolution of cellular organelles are reviewed. The mitochondrial genomes of eukaryotes differ considerably in size and structural organization mainly due to the length variation in noncoding regions and the presence of introns. The mitochondrial genomes of angiosperms are the largest and most complicated. Gene content in eukaryotic mitochondrial genomes is similar. They usually encode all types of rRNA, a complete or partial complement of tRNA, and a limited number of proteins essential for mitochondrial functions. In all eukaryotes studied, mitochondrial genomes code for two highly hydrophobic proteins involved in respiration, cytochrome b and subunit 1 of cytochrome oxidase. Genome structure and gene content in plastids, mainly in higher plant chloroplasts, are highly conserved. Plastid genomes of algae are more variable in gene composition and contain several unique genes absent in the chloroplast DNA of higher plants. Plastid genomes encode proteins involved in transcription and translation, as well as proteins of the photosynthetic apparatus. Both types of cellular organelles are supposed to be of endosymbiotic origin. Modern plastids originate from a cyanobacterial ancestor. Alpha-proteobacteria, especially the most mitochondrion-like rickettsia, gave rise to mitochondria. The origin of plastids of higher plants and green algae as a result of primary endosymbiosis and that of other algal lineages by secondary endosymbiosis are briefly discussed.

Dicyemida and Orthonectida: Two Stories of Body Plan Simplification

“…The partitioning of mtDNA into circular molecules is a rare feature for the animal mitochondrial genomes (Odintsova and Yurina, 2005; Burger et al, 2012; Kolesnikov and Gerasimov, 2012; Smith and Keeling, 2015; Lavrov and Pett, 2016, for review). In bilaterians, the mtDNA is fragmented into a large number of mini-chromosomes in the cyst-forming nematodes Globodera spp.…”

Reconstruction of the lipid metabolism for the microalga Monoraphidium neglectum from its genome sequence reveals characteristics suitable for biofuel production

“…This finding is supported by the large variance in the chloroplast genome size encountered among sequenced algal genomes [35,36]. In contrast, when compared to the chloroplast genomes of algae, conservation of structure and gene content of chloroplasts appears to be greater in plants.…”

Evolutionary inference across eukaryotes identifies multiple pressures favoring mitochondrial gene retention

“…The two genes most 5 retained by mitochondrial genomes throughout life, cob and cox1, are the most energetically central components of their complexes (Complex III and Complex IV respectively). The sdh [2][3][4] genes controlling Complex II, and cox [2][3], which play an important role in Complex IV but are less central than cox1, represent intermediate points on this spectrum. Many organisms do not encode any Complex II subunits in mtDNA: those that do so retain the energetically most central sdh [2][3][4] genes and not sdh1.…”

“…The sdh [2][3][4] genes controlling Complex II, and cox [2][3], which play an important role in Complex IV but are less central than cox1, represent intermediate points on this spectrum. Many organisms do not encode any Complex II subunits in mtDNA: those that do so retain the energetically most central sdh [2][3][4] genes and not sdh1. cox [2][3] are retained in the mitochondria of most but not all organisms.…”

“…Mitochondria are the result of an endosymbiotic event [1], where a free-living organism resembling an αproteobacterium was engulfed by another cell billions of years ago. Since this event, a pronounced loss of mitochondrially-encoded genes has occurred, with genes either transferred to the host nucleus or lost completely [2,3,4,5]. This endosymbiosis and the subsequent evolution of mitochondrial genomes are among the most important processes in biological history, giving rise to eukaryotic life and hypothesised as facilitating the higher energy output required for the evolution of complexity and multicellularity [6].…”