Abstract
The two carboxylation reactions performed by phosphoenolpyruvate carboxylase (PEPC) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) are vital in the fixation of inorganic carbon for C4 plants. The abundance of PEPC is substantially elevated in C4 leaves, while the location of Rubisco is restricted to one of two chloroplast types. These differences compared with C3 leaves have been shown to result in convergent enzyme optimization in some C4 species. Investigation into the kinetic properties of PEPC and Rubisco from Kranz C4, single cell C4, and C3 species in Chenopodiaceae s. s. subfamily Suaedoideae showed that these major carboxylases in C4 Suaedoideae species lack the same mutations found in other C4 systems which have been examined; but still have similar convergent kinetic properties. Positive selection analysis on the N-terminus of PEPC identified residues 364 and 368 to be under positive selection with a posterior probability >0.99 using Bayes empirical Bayes. Compared with previous analyses on other C4 species, PEPC from C4 Suaedoideae species have different convergent amino acids that result in a higher K m for PEP and malate tolerance compared with C3 species. Kinetic analysis of Rubisco showed that C4 species have a higher catalytic efficiency of Rubisco (k catc in mol CO2 mol(-1) Rubisco active sites s(-1)), despite lacking convergent substitutions in the rbcL gene. The importance of kinetic changes to the two-carboxylation reactions in C4 leaves related to amino acid selection is discussed.
Highlights
When organisms develop the same solution to an abiotic or biotic stress resulting in a similar character state, it is referred to as convergent evolution or phenotypic convergence
The results show that the C4 species have divergent amino acid positive selection resulting in convergent C4-type kinetic properties for phosphoenolpyruvate carboxylase (PEPC) and Rubisco
To complement previous sequence and phylogenetic information on PEPC in Suaedoideae (Rosnow et al, 2014), N-terminal PEPC sequence was obtained for 19 species (S. heterophylla, Salsola genistoides, and Salsola divaricata were not included) using homologous upstream primers that overlapped with known C-terminal ppc-1 sequence
Summary
When organisms develop the same solution to an abiotic or biotic stress resulting in a similar character state, it is referred to as convergent evolution or phenotypic convergence. One of the most documented convergent phenotypes in plants is the repeated development of C4 photosynthesis, an adaptation that uses four carbon acids to increase photosynthesis under conditions where carbon assimilation can be limited by high photorespiration (Sage et al, 2012). Times that C4 independently developed (at least 66) makes it an extremely useful phenotype for analysing the genetics of adaptations (Christin et al, 2010; Sage et al, 2011). Atmospheric CO2 is initially converted into bicarbonate (HCO3−) by carbonic anhydrase and the chloroplasts generate phosphoenolpyruvate (PEP) from pyruvate by pyruvate, Pi dikinase. How C4 photosynthesis is regulated, by the level of enzymes and their kinetic properties, their state of activation, and their control by allosteric effectors, is important for understanding the mechanism and how they accomplish high rates of photosynthesis under CO2 limiting conditions
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
