About this Research Topic
C4 photosynthesis is a remarkable example of convergent evolution, having evolved in at least 61 independent phylogenetic lineages over the last 60 million years. In C4 species, Rubisco operates close to its maximal rate through the avoidance of the oxygenation reaction. This is accomplished via the establishment of a molecular CO2 pump that delivers carbon in the form of C4 acid intermediates to a spatially sequestered Rubisco. This carbon pump can be set up using a diverse array of complex biochemical and morphological modifications relative to the basal C3 photosynthetic state. Most C4 species use Kranz anatomy to create the carbon pump, wherein mesophyll cells surround highly developed bundle sheath cells that are concentrically arranged in a ring around the vasculature. In a small number of species, special organellar arrangements are used to achieve high carbon concentrations around Rubisco within a single cell. In addition, inducible forms of C4 photosynthesis have evolved and there are many extant C3-C4 intermediates with varying degrees of C4 anatomy and physiology.
The sheer number of times that C4 photosynthesis has evolved, in addition to C3-C4 intermediate species, indicates that evolution from the ancestral C3 photosynthetic state is both elastic and relatively straightforward. Correspondingly, a number of extant genes have been recruited to C4 functions from the basal C3 state through regulatory and/or enzymatic modifications. However, the genetics controlling the development of the C4 syndrome is not yet well enough resolved that a C3 plant can be converted to C4 in the lab. Such a conversion applied to C3 crops would be highly desirable because C4 crops have higher yields and increased nitrogen and water use efficiency relative to C3 crops. Replicating the C4 process in C3 crops such as rice would therefore help support a growing world population.
The aim of this Research Topic is to better understand the evolution and function of C4 photosynthesis. We welcome Original Research, Reviews and Opinion articles focused on:
- Comparative approaches that employ distinct phylogenetic lineages of this convergent trait to expand our knowledge of the genetics underpinning C4 anatomy, biochemistry, physiology and metabolism
- Comparative approaches that employ natural variation (C3, C3-C4, C4), mutant or hybrid populations to expand the known limits of C4 photosynthesis and/or provide greater resolution for its genetic basis
- Regulatory mechanisms controlling the development or function of the C4 syndrome
- Changes to enzymatic function or regulation necessary to operate C4 photosynthesis
- Identification of candidate gene(s) and/or functional validation of those gene(s) in establishing C4 biochemistry and/or morphology during leaf development or their involvement in C4 metabolism of mature leaves
- Elucidation of the evolutionary steps necessary and/or sufficient for C4
- Replicating the C4 pathway and/or anatomy in C3 species
Keywords: C4 photosynthesis, Convergent evolution, Comparative biology, Genetic variation, Regulatory mechanisms
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