Systematic Comparison of C3 and C4 Plants Based on Metabolic Network Analysis

Abstract

BackgroundThe C4 photosynthetic cycle supercharges photosynthesis by concentrating CO2 around ribulose-1,5-bisphosphate carboxylase and significantly reduces the oxygenation reaction. Therefore engineering C4 feature into C3 plants has been suggested as a feasible way to increase photosynthesis and yield of C3 plants, such as rice, wheat, and potato. To identify the possible transition from C3 to C4 plants, the systematic comparison of C3 and C4 metabolism is necessary.ResultsWe compared C3 and C4 metabolic networks using the improved constraint-based models for Arabidopsis and maize. By graph theory, we found the C3 network exhibit more dense topology structure than C4. The simulation of enzyme knockouts demonstrated that both C3 and C4 networks are very robust, especially when optimizing CO2 fixation. Moreover, C4 plant has better robustness no matter the objective function is biomass synthesis or CO2 fixation. In addition, all the essential reactions in C3 network are also essential for C4, while there are some other reactions specifically essential for C4, which validated that the basic metabolism of C4 plant is similar to C3, but C4 is more complex. We also identified more correlated reaction sets in C4, and demonstrated C4 plants have better modularity with complex mechanism coordinates the reactions and pathways than that of C3 plants. We also found the increase of both biomass production and CO2 fixation with light intensity and CO2 concentration in C4 is faster than that in C3, which reflected more efficient use of light and CO2 in C4 plant. Finally, we explored the contribution of different C4 subtypes to biomass production by setting specific constraints.ConclusionsAll results are consistent with the actual situation, which indicate that Flux Balance Analysis is a powerful method to study plant metabolism at systems level. We demonstrated that in contrast to C3, C4 plants have less dense topology, higher robustness, better modularity, and higher CO2 and radiation use efficiency. In addition, preliminary analysis indicated that the rate of CO2 fixation and biomass production in PCK subtype are superior to NADP-ME and NAD-ME subtypes under enough supply of water and nitrogen.

A sedimentação em uma abordagem sistêmica

“…A fotossíntese nas plantas C3 é descrita a seguir e esquematizada na Figura 11. Na primeira etapa da fotossíntese, ocorre a carboxilase-oxigenase da ribulose-bisfosfato (RuBP) dentro dos cloroplastos (Ehleringer & Cerling 2001, Wang et al 2012.…”

“…Os gases presentes na água, inclusive o CO 2 produzido pela decomposição da matéria orgânica e dissolução de carbonatos podem ser devolvidos à atmosfera. presença de O 2 (Ehleringer & Cerling 2001, Wang et al 2012 (Ehleringer & Cerling 2001).…”

“…Nas plantas C4, as atividades fotossintéticas ocorrem em dois tecidos anatômica e bioquimicamente distintos das suas folhas, as células da bainha vascular e as células do mesófilo (Wang et al 2012). Nas células do mesófilo, uma enzima muito ativa, a fosfoenolpiruvato (PEP) carboxilase, fixa o CO 2 em oxaloacetato (OAA) (uma molécula que possui quatro carbonos) (Ehleringer & Cerling 2001).…”

Expression Profiles of <i>psbA, ALS, EPSPS</i>, and Other Chloroplastic Genes in Response to PSII-, ALS-, and EPSPS-Inhibitor Treatments in <i>Kochia scoparia</i>

“…In C3 plants, atmospheric CO 2 is fixed through the Calvin cycle, catalyzed by Rubisco inside the chloroplast of mesophyll cells [2]. On the other hand, in C4 plants such as kochia, photosynthetic activities are partitioned anatomically and biochemically in mesophyll and bundle sheath cells [2].…”

“…In C3 plants, atmospheric CO 2 is fixed through the Calvin cycle, catalyzed by Rubisco inside the chloroplast of mesophyll cells [2]. On the other hand, in C4 plants such as kochia, photosynthetic activities are partitioned anatomically and biochemically in mesophyll and bundle sheath cells [2]. This partitioning of photosynthetic activities into distinct regions (Kranz anatomy) in C4 plants helps to reduce photorespiration and increase the photosynthetic efficiency [3].…”