what is the evolutionary advantage for organisms that are able to photosynthesize

• Journal List
• Plant Physiol
• five.154(ii); 2010 Oct
• PMC2949000

Establish Physiol. 2010 Oct; 154(2): 434–438.

Early on Evolution of Photosynthesisⁱ

Received 2010 Jun 20; Accepted 2010 Jun thirty.

Photosynthesis is the simply significant solar energy storage process on Earth and is the source of all of our food and most of our energy resources. An understanding of the origin and evolution of photosynthesis is therefore of substantial interest, as information technology may help to explicate inefficiencies in the process and signal the way to attempts to improve various aspects for agricultural and energy applications.

A wealth of evidence indicates that photosynthesis is an ancient procedure that originated non long later on the origin of life and has evolved via a circuitous path to produce the distribution of types of photosynthetic organisms and metabolisms that are constitute today (Blankenship, 2002; Björn and Govindjee, 2009). Figure 1 shows an evolutionary tree of life based on small-subunit rRNA analysis. Of the three domains of life, Bacteria, Archaea, and Eukarya, chlorophyll-based photosynthesis has only been establish in the bacterial and eukaryotic domains. The power to practise photosynthesis is widely distributed throughout the bacterial domain in 6 different phyla, with no credible design of development. Photosynthetic phyla include the cyanobacteria, proteobacteria (purple bacteria), green sulfur bacteria (GSB), firmicutes (heliobacteria), filamentous anoxygenic phototrophs (FAPs, also frequently called the dark-green nonsulfur leaner), and acidobacteria (Raymond, 2008). In some cases (cyanobacteria and GSB), substantially all members of the phylum are phototrop2hic, while in the others, in particular the proteobacteria, the vast bulk of species are not phototrophic.

Small subunit rRNA evolutionary tree of life. Taxa that comprise photosynthetic representatives are highlighted in color, with green highlighting indicating a type I RC, while purple highlighting indicates a type II RC. The red arrow indicates the endosymbiotic event that formed eukaryotic chloroplasts. Tree adjusted from Step (1997).

Overwhelming bear witness indicates that eukaryotic photosynthesis originated from endosymbiosis of cyanobacterial-like organisms, which ultimately became chloroplasts (Margulis, 1992). So the evolutionary origin of photosynthesis is to be found in the bacterial domain. Significant show indicates that the current distribution of photosynthesis in leaner is the result of substantial amounts of horizontal cistron transfer, which has shuffled the genetic information that codes for diverse parts of the photosynthetic apparatus, so that no one elementary branching diagram tin can accurately represent the development of photosynthesis (Raymond et al., 2002). Nonetheless, there are some patterns that tin be discerned from detailed analysis of the various parts of the photosynthetic apparatus, so some conclusions can be fatigued. In addition, the recent explosive growth of available genomic data on all types of photosynthetic organisms promises to let substantially more than progress in unraveling this circuitous evolutionary process.

While we often talk about the evolution of photosynthesis as if it were a concerted procedure, information technology is more useful to consider the evolution of various photosynthetic subsystems, which have clearly had distinct evolutionary trajectories. In this cursory review we volition discuss the evolution of photosynthetic pigments, reaction centers (RCs), light-harvesting (LH) antenna systems, electron send pathways, and carbon fixation pathways. These subsystems clearly collaborate with each other, for example both the RCs and antenna systems utilize pigments, and the electron ship chains interact with both the RCs and the carbon fixation pathways. Still, to a significant degree they can be considered every bit modules that can exist analyzed individually.

ORIGINS OF PHOTOSYNTHESIS

We know very fiddling about the earliest origins of photosynthesis. There accept been numerous suggestions equally to where and how the process originated, but there is no direct evidence to support whatever of the possible origins (Olson and Blankenship, 2004). At that place is suggestive evidence that photosynthetic organisms were nowadays approximately iii.ii to 3.5 billion years ago, in the class of stromatolites, layered structures similar to forms that are produced by some modern blue-green alga, as well as numerous microfossils that have been interpreted as arising from phototrophs (Des Marais, 2000). In all these cases, phototrophs are not certain to have been the source of the fossils, just are inferred from the morphology or geological context. There is also isotopic evidence for autotrophic carbon fixation at 3.7 to 3.8 billion years ago, although at that place is nothing that indicates that these organisms were photosynthetic. All of these claims for early photosynthesis are highly controversial and have engendered a neat bargain of spirited discussion in the literature (Buick, 2008). Prove for the timing of the origin of oxygenic photosynthesis and the ascent of oxygen in the atmosphere is discussed below. The accumulated prove suggests that photosynthesis began early in Earth'southward history, but was probably not 1 of the earliest metabolisms and that the primeval forms of photosynthesis were anoxygenic, with oxygenic forms arising significantly later.

PHOTOSYNTHETIC PIGMENTS

Chlorophylls are essential pigments for all phototrophic organisms. Chlorophylls are themselves the product of a long evolutionary evolution, and can possibly exist used to help understand the evolution of other aspects of photosynthesis. Chlorophyll biosynthesis is a circuitous pathway with 17 or more steps (Beale, 1999). The early part of the pathway is identical to heme biosynthesis in almost all steps and has conspicuously been recruited from that older pathway. The subsequently steps include the insertion of magnesium and the elaboration of the ring organisation and its substituents. The earliest version of the pathway (and that used by most modern anoxygenic photosynthetic organisms) almost certainly was anaerobic, both not requiring and not tolerating the presence of O_two. However, all modern oxygenic photosynthetic organisms now require O_ii as an oxidant at several steps in the pathway. This has been explained in terms of gene replacement of the genes coding for the enzymes at these steps, with the result that the overall pathway is unchanged simply the enzymes at key steps are completely different in different groups of phototrophs (Raymond and Blankenship, 2004).

A key concept in using chlorophyll biosynthesis pathways to infer the development of photosynthesis is the Granick hypothesis, which states that the biosynthetic pathway of chlorophyll recapitulates the evolutionary sequence (Granick, 1965). This is an appealing idea and probably at to the lowest degree partly true. However, in some cases, in particular the situation of chlorophyll and bacteriochlorophyll, it has been argued that the strict version of the Granick hypothesis is misleading and other interpretations are more than probable (Blankenship, 2002; Blankenship et al., 2007).

All photosynthetic organisms contain carotenoids, which are essential for photoprotection, usually also function as accompaniment pigments, and in many cases serve as primal regulatory molecules. Carotenoids, different chlorophylls, are likewise constitute in many other types of organisms, so their evolutionary history may reverberate many other functions in addition to photosynthesis (Sandman, 2009).

REACTION CENTERS

The RC complex is at the heart of photosynthesis; so much attention has been paid to understand the evolution of RCs. A wealth of evidence, including structural, spectroscopic, thermodynamic, and molecular sequence analysis, clearly segregates all known RCs into 2 types of complexes, called type I and type II (Blankenship, 2002). Anoxygenic phototrophs have just one type, either type I or Ii, while all oxygenic phototrophs have one of each type. The primary distinguishing feature of the two types of RCs are the early electron acceptor cofactors, which are FeS centers in type I RCs and pheophytin/quinone complexes in blazon Ii RCs. The distribution of RC types on the tree of life is shown in Effigy one and a comparative electron send diagram that compares the dissimilar RCs in dissimilar types of organisms is shown in Figure ii, with type I RCs color coded green and type Ii RCs colour coded purple.

Electron transport diagram indicating the types or RCs and electron send pathways constitute in different groups of photosynthetic organisms. The color coding is the aforementioned every bit for Figure one and highlights the electron acceptor portion of the RC. Effigy courtesy of Martin Hohmann-Marriott.

Further analysis strongly suggests that all RCs take evolved from a unmarried mutual ancestor and have a similar protein and cofactor structure. This is clearly seen when structural overlays of both type I and Ii RCs are made, showing a remarkably conserved iii-dimensional protein and cofactor structure, despite merely minimal residue sequence identity (Sadekar et al., 2006). These comparisons have been used to derive structure-based evolutionary copse that do not rely on sequence alignments. Figure three shows a schematic evolutionary tree of RCs that is derived from this sort of assay. It proposes that the earliest RC was intermediate between type I and II (blazon one.5) and that multiple gene duplications have given ascent to the heterodimeric (ii related notwithstanding distinct proteins that course the core of the RC) complexes that are institute in about modern RCs.

Schematic evolutionary tree showing the evolution of the different types of RC complexes in different types of photosynthetic organisms. This tree is based on structural comparisons of RCs by Sadekar et al. (2006). Blue color coding indicates poly peptide homodimer, while red indicates poly peptide heterodimer complexes. Red stars point gene duplication events that led to heterodimeric RCs. Helio, Heliobacteria; GSB, green sulfur bacteria; FAP, filamentous anoxygenic phototroph.

A second of import issue that relates to RC evolution is the question of how both blazon I and 2 RCs came to be in blue-green alga, while all other photosynthetic prokaryotes have merely a single RC. The diverse proposals that take been made to explain this fact can all be divided into either fusion or selective loss scenarios or variants thereof (Blankenship et al., 2007). In the fusion hypothesis, the two types of RCs develop separately in anoxygenic photosynthetic bacteria and are and so brought together by a fusion of two organisms, which subsequently adult the ability to oxidize water. In the selective loss hypothesis, the two types of RCs both evolved in an ancestral organism and then loss of 1 or the other RC gave rise to the organisms with just one RC, while the ability to oxidize h2o was added afterwards. Both scenarios accept proponents, and it is not yet possible to cull between them.

ELECTRON Transport CHAINS

The chief photochemistry and several of the early secondary electron transfer reactions have place within the RC complex. However, boosted electron transfer processes are necessary before the process of energy storage is complete. These include the cytochrome bc _one and b _sixf complexes. These complexes oxidize quinols produced past photochemistry in type 2 RCs or via cyclic processes in type I RCs and pumps protons across the membrane that in plough contribute to the proton motive force that is used to make ATP. All phototrophic organisms have a cytochrome bc _i or b ₆f circuitous of mostly like architecture, with the exception of the FAP phylum of anoxygenic phototrophs (Yanyushin et al., 2005). This grouping contains instead a completely dissimilar type of circuitous that is called alternative complex Iii. The evolutionary origin of this complex is not notwithstanding clear. While the cytochrome bc ₁ and b ₆f complexes are like in many means, the cytochrome c _i and f subunits are very dissimilar and are almost certainly of distinct evolutionary origin (Baniulis et al., 2008).

ANTENNA SYSTEMS

All photosynthetic organisms contain a light-gathering antenna arrangement, which functions to collect excitations and transfer them to the RC where the excited state energy is used to drive photochemistry (Green and Parson, 2003). While the presence of an antenna is universal, the structure of the antenna complexes and even the types of pigments used in them is remarkably varied in dissimilar types of photosynthetic organisms. This very strongly suggests that the antenna complexes have been invented multiple times during the grade of evolution to adapt organisms to particular photic environments. So while evolutionary relationships are clear among some categories of antennas, such as the LH1 and LH2 complexes of purple bacteria and the LHCI and LHCII complexes of eukaryotic chloroplasts, it is not possible to relate these wide categories of antennas to each other in any meaningful way. This is in contrast to the RCs, where all bachelor show clearly points to a unmarried origin that has subsequently undergone a complex evolutionary development.

CARBON FIXATION PATHWAYS

Most phototrophic organisms are capable of photoautotrophic metabolism, in which inorganic substrates such as h2o, H₂S, CO_ii, or HCO_three ⁻ are utilized forth with light energy to produce organic carbon compounds and oxidized donor species. Nonetheless, there are some groups of phototrophs that cannot carry out photoautotrophic metabolism and there are at least three entirely divide autotrophic carbon fixation pathways that are plant in different types of organisms (Thauer, 2007). By far the dominant carbon fixation pathway is the Calvin-Benson cycle, which is constitute in all oxygenic photosynthetic organisms, and also in nigh royal leaner. The GSB use the reverse tricarboxylic acrid cycle, and many of the FAPs use the 3-hydroxypropionate cycle (Zarzycki et al., 2009). The Gram-positive heliobacteria lack any known autotrophic carbon fixation pathway and usually grow photoheterotrophically (Asao and Madigan, 2010). Similarly, the aerobic anoxygenic phototrophs, which are closely related to the majestic bacteria, lack any apparent power to fix inorganic carbon. In the latter case, information technology seems most probable that the antecedent of this group contained the Calvin-Benson cycle but lost the genes because of their obligate aerobic lifestyle (Swingley et al., 2007).

The carbon fixation mechanism is thus similar to the antennas, in that several entirely separate solutions have been adopted by different classes of phototrophic organisms. This would be consequent with the idea that the earliest phototrophs were photoheterotrophic, using calorie-free to assimilate organic carbon, instead of being photoautotrophic. The ability to set up inorganic carbon was then added to the metabolism somewhat later during the form of evolution, maybe borrowing carbon fixation pathways that had developed earlier in autotrophic nonphotosynthetic organisms.

TRANSITION TO OXYGENIC PHOTOSYNTHESIS

Perhaps the most widely discussed yet poorly understood issue in the evolution of photosynthesis is the invention of the ability to use water as an electron donor, producing O₂ as a waste production and giving rise to what is now chosen oxygenic photosynthesis. The production of O₂ and its subsequent accumulation in the atmosphere forever changed the World and permitted the development of advanced life that utilized the O₂ during aerobic respiration. Several lines of geochemical evidence indicate that complimentary O₂ began to accrue in the atmosphere by 2.4 billion years agone, although the ability to do oxygenic photosynthesis probably began somewhat before (Buick, 2008). In order for O_ii to accrue, it is necessary that both the biological machinery needed to produce information technology has evolved, simply also the reduced carbon produced must be buried by geological processes, which are controlled past geological processes such as plate tectonics and the buildup of continents. So the buildup of O₂ in the atmosphere represents a coming together of the biology that gives ascension to O_two production and the geology that permits O₂ to accrue.

Oxygen is produced past PSII in the oxygen evolving middle, which contains a tetranuclear manganese circuitous. The evolutionary origin of the oxygen evolving eye has long been a mystery. Several sources have been suggested, simply so far no convincing evidence has been constitute to resolve this issue (Raymond and Blankenship, 2008). The possibility that functional intermediate stages existed that connect the anoxygenic type II RCs to PSII seems likely (Blankenship and Hartman, 1998).

Decision

The process of photosynthesis originated early on in Earth's history, and has evolved to its electric current mechanistic multifariousness and phylogenetic distribution past a circuitous, nonlinear procedure. Current evidence suggests that the primeval photosynthetic organisms were anoxygenic, that all photosynthetic RCs take been derived from a single source, and that antenna systems and carbon fixation pathways have been invented multiple times.

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Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2949000/