Interactions of photosynthesis with genome size and function

Abstract

Photolithotrophs are divided between those that use water as their electron donor (Cyanobacteria and the photosynthetic eukaryotes) and those that use a different electron donor (the anoxygenic photolithotrophs, all of them Bacteria). Photolithotrophs with the most reduced genomes have more genes than do the corresponding chemoorganotrophs, and the fastest-growing photolithotrophs have significantly lower specific growth rates than the fastest-growing chemoorganotrophs. Slower growth results from diversion of resources into the photosynthetic apparatus, which accounts for about half of the cell protein. There are inherent dangers in (especially oxygenic) photosynthesis, including the formation of reactive oxygen species (ROS) and blue light sensitivity of the water spitting apparatus. The extent to which photolithotrophs incur greater DNA damage and repair, and faster protein turnover with increased rRNA requirement, needs further investigation. A related source of environmental damage is ultraviolet B (UVB) radiation (280–320 nm), whose flux at the Earth's surface decreased as oxygen (and ozone) increased in the atmosphere. This oxygenation led to the requirements of defence against ROS, and decreasing availability to organisms of combined (non-dinitrogen) nitrogen and ferrous iron, and (indirectly) phosphorus, in the oxygenated biosphere. Differential codon usage in the genome and, especially, the proteome can lead to economies in the use of potentially growth-limiting elements

Iron deficiency increases growth and nitrogen-fixation rates of phosphorus-deficient marine cyanobacteria

“…For Trichodesmium, the cell size response appears instead to consist of increases in filament mass under Fe-replete, P-limited conditions. Various major cellular elemental pools could be involved in controlling cell size plasticity and Fe and P-use efficiencies for growth, including those associated with the nitrogenase complex, photosynthetic electron transport (Raven 1988), polyphosphates (Rao et al, 2009), Fe storage compounds such as ferritin (Keren et al, 2004) or other proteins and nucleic acids (Raven et al, 2013).…”

The Evolutionary Origin of a Terrestrial Flora

“…These genomes are quite small, ranging from 154.5 kb in Arabidopsis, to 191 kb in the red alga Porphyra, to 420 kb in the chlorophyte green alga Volvox, and compared to genome sizes in free-living cyanobacteria that range from 1643 to 12,073 kb [25,26]. This means that a typical plastid genome is on the order of 5% the size of a free-living cyanobacterial genome, and consequently that the organelles are completely dependent upon the host cell to encode, transcribe, and translate most proteins, as well as to carry out many other metabolic processes [27].…”

Nitrogen and sulfur assimilation in plants and algae

“…While most algae and plants can also take up and assimilate nitrate, there are significant exceptions, such as some strains of the very abundant (in terms of cell numbers) warm-water marine phytoplanktonic cyanobacterium Prochlorocococcus (Raven, 1984;Raven et al, 1992bRaven et al, , 2013. The natural environment typically has a mixture of sources of combined N. Reduced N forms predominate in the surface oligotrophic ocean, where recycling of N derived from living organisms into phytoplankton is rapid and there is little scope for nitrifiers.…”