Search

Proteins are modular functionalities regulating multiple cellular activities in prokaryotes and eukaryotes. As a consequence of higher plants adapting to arid and thermal conditions, C4 photosynthesis is the carbon fixation process involving multi-enzymes working in a coordinated fashion. However, how these enzymes interact with each other and whether they co-evolve in parallel to maintain interactions in different plants remain elusive to date. Here, we report our findings on the global protein co-evolution relationship and local dynamics of co-varying site shifts in key C4 photosynthetic enzymes. We found that in most of the selected key C4 photosynthetic enzymes, global pairwise co-evolution events exist to form functional couplings. Besides, protein–protein interactions between these enzymes may suggest their unknown functionalities in the carbon delivery process. For PEPC and PPCK regulation pairs, pocket formation at the interactive interface are not necessary for their function. This feature is distinct from another well-known regulation pair in C4 photosynthesis, namely, PPDK and PPDK-RP, where the pockets are necessary. Our findings facilitate the discovery of novel protein regulation types and contribute to expanding our knowledge about C4 photosynthesis. [ABSTRACT FROM AUTHOR]

Drought is one of the major stress which affects agricultural crop productivity around the world. In this study the role of Phos phoenol pyruvate carboxylase (PEPC, EC 4.1.1.31), NADP-malic enzyme (NADP-ME, EC 1.1.1.40), and pyruvate, phosphate dikinase (PPDK, EC 2.7.9.1) in different onion cultivars (Allium cepa L.) under drought stress was investigated. An elevated specific activity of these three enzymes was monitored in onion cultivars after 8 h of drought stress. With the increasing concentration of drought there was an increase in C4 enzyme activities. PEPC showed 3.5-fold increase after 24 h, NADP-ME 3.9-fold, and PPDK 3.2-fold increase was observed in Arkalalima (AL)onion after 48 h when compared to control. Statistical analysis including regression analysis suggested significant results to onion drought resistant cultivars under drought stress condition. The results revealed that the variety AL exhibited best response followed by Arkakirthaman (AK) and Bellary(BL). Therefore PEPC, PPDK and NADPME participate in the drought response of onion, a C3 Plant. Future research will allow further understanding of the drought stress mechanism of adaptation of the onion germplasm to drought. [ABSTRACT FROM AUTHOR]

• PPDK and PEPC, in lieu of Rubisco, increased almost two-fold for ammonium tolerant species • Overproduction of PEPC and PPDK led to improved photosynthesis, better ammonium assimilation and overall ammonium detoxification • These findings propose likelihood for the existence of a complementary ammonium detoxification pathway that targets carbon metabolism Possible ammonium detoxification mechanisms have been proposed recently, on submerged macrophytes, evidently illustrating that glutamate dehydrogenase (GDH) plays a greater role in ammonium detoxification compared to the primary glutamine synthetase/glutamate oxaloacetate transaminase (GS/GOGAT) pathway. In the current investigation, we cultured three submerged macrophytes to extreme concentrations of [NH 4 +-N] of up to 50 mg/L with the aim of clarifying the interaction between carbon and nitrogen metabolisms. The activities of carboxylation enzymes pyruvate orthophosphate dikinase (PPDK) and phosphoenolpyruvate carboxylase (PEPC), in lieu of Rubisco, increased almost two-fold for ammonium tolerant species P. maackianus and M. spicatum , compared with the sensitive species P. lucens. While these enzymes are well known for their central role in CO 2 fixation, their inference in conferring resistance to ammonium stress has not been well elucidated before. In this study, we demonstrate that the overproduction of PEPC and PPDK led to improved photosynthesis, better ammonium assimilation and overall ammonium detoxification in M. spicatum and P. maackianus. These findings propose likelihood for the existence of a complementary ammonium detoxification pathway that targets carbon metabolism, thus, presenting a relatively efficient linkage between nitrogen and carbon metabolisms and identify candidate species for practical restoration of fresh water resources. [ABSTRACT FROM AUTHOR]

Remobilization of leaf nitrogen (N) contributes greatly to grain N in maize, but leads to low photosynthetic rate (P n ). P n is determined by various N components involving in light harvest and CO 2 reduction. However, it is less clear which N component is the major contributor for the reduction of photosynthesis in modern stay-green maize hybrids. In this study, we analyzed the relationship between remobilization of different N components and P n during grain filling stage under low N (no N application) and high N (180 kg N ha −1 ) in a field experiment. The remobilization efficiency of photosynthetic enzymes (PEPc, PPDK and Rubisco) in the leaf was much higher than that of thylakoid N and other N components. Low N supply increased the remobilization efficiency of all the leaf N components. During grain filling stage, the amount of all the N components decreased together with P n . The ratio of P n to the N in the PEPc, PPDK and Rubisco kept increase in the whole grain filling stage, while the ratio of P n to chlorophyll and thylakoid-N decreased. Correlation analysis indicated that P n was more related to the content of photosynthetic enzymes than to chlorophyll and thylakoid N. It is concluded that photosynthetic enzymes serve as an N storage reservoir at early grain filling stage and their degradation is critical in the reduction of P n during later grain filling stage. Future breeding targets may be focused on enhancing the efficiency of photosynthetic enzymes during late grain filling stage. [ABSTRACT FROM AUTHOR]

Aluminum is one of the most important heavy metals inducing stress during plant growth and development. In this study, transgenic rice (Oryza sativa L., cv. Kitaake) plants expressing the maize C4 PEPC and PPDK genes were evaluated for aluminum tolerance. A 4.3 and 19.1 folds increase of PPDK and PEPC activities in transgenic rice produced increases in root exudation of oxalate, malate, and citrate (1.20, 1.41, and 1.65 times, respectively) compared to untransformed (WT) plants. Transgenic rice had enhanced aluminum tolerance compared to WT based on chlorophyll fluorescence and chlorophyll levels. Transgenic plants under aluminum stress also had decreased lipid membrane oxidative damage and higher levels of ROS-scavenging enzyme activity. The PEPC and PPDK genes play an important role in aluminum stress tolerance by increasing the effluxes of organic acids. [ABSTRACT FROM AUTHOR]

Ottelia alismoides is a constitutive C4 plant and bicarbonate user, and has facultative crassulacean acid metabolism (CAM) at low CO2. Acclimation to a factorial combination of light and CO2 showed that the ratio of phosphoenolpyruvate carboxylase (PEPC) to ribulose-bisphosphate carboxylase/oxygenase (Rubisco) (>5) is in the range of that of C4 plants. This and short-term response experiments showed that the activity of PEPC and pyruvate phosphate dikinase (PPDK) was high even at the end of the night, consistent with night-time acid accumulation and daytime carbon fixation. The diel acidity change was maximal at high light and low CO2 at 17-25 μequiv g-1 FW. Decarboxylation proceeded at ~2-3 μequiv g-1 FW h-1, starting at the beginning of the photoperiod, but did not occur at high CO2; the rate was greater at high, compared with low light. There was an inverse relationship between starch formation and acidity loss. Acidity changes account for up to 21% of starch production and stimulate early morning photosynthesis, but night-time accumulation of acid traps <6% of respiratory carbon release. Ottelia alismoides is the only known species to operate CAM and C4 in the same tissue, and one of only two known aquatic species to operate CAM and bicarbonate use. [ABSTRACT FROM AUTHOR]

To improve the efficiency of CO fixation in C photosynthesis, C-cycle genes were overexpressed in Arabidopsis plants. In this study, a full-length cDNA for pyruvate orthophosphate dikinase ( PPDK) with 971 amino acids was isolated from Zea mays using LA-PCR. The PPDK gene (GenBank accession number GU363532) and the phosphoenolpyruvate carboxylase ( PEPC) gene (GenBank accession number: FJ415327) derived from a previous study were introduced into wild-type Arabidopsis both individually and in combination. The vector pCAMBIA3301 (p3301) was introduced into Arabidopsis as a control using an Agrobacterium-mediated system. The integration, transcription, and translation of the PPDK and the PEPC genes were confirmed by Southern blot, quantitative real-time PCR, and Western blot analysis. The average enzyme activity of C- PPDK and C- PEPC peaked at 4.63- and 5.81-fold compared to that of controls, respectively. The insertion of PPDK was found to increase the activity of PEPCase and vice versa. The photosynthetic rates of C- PPDK, C- PEPC, and C- PKC( PPDK+ PEPC) transgenic lines increased to 123.3, 136.4, and 146.6 % compared to that of controls, respectively. [ABSTRACT FROM AUTHOR]