The Cultivation Strategy Of C₄Prototype

According to the difference of the CO2assimilation mode during thephotosynthesis, higher plants can be divided into C3plants, C4plants, andcrassulacean acid metabolism (CAM) plants. Compared with C3plants, the typicaldouble-cell C4plant leaves have Kranz structure and CO2concentrating mechanism.With the increase of population, human beings will face great challenge by shortsupply of grain yield. The main grain crops, like wheat and rice, carry out C3photosynthetic pathway. Therefore, change from C3to C4plants in gene structure hasimportant practical significance.Previous studies revealed that C4photosynthesis could not be achieved throughtransferring one or more key enzymes into C3plants. In this study, the Arabidopsisthaliana was chosen as the material to construct C4photosynthetic prototype. The C4type PEPC could catalyze phosphoenolpyruvate (PEP) into oxaloacetic acid (OAA)through β-carboxylation reaction by using phosphoenolpyruvate carboxylase (PEPC).After that, malic acid or aspartic acid could be generated from oxaloacrtic acid underthe action of malic enzyme. As one of the key enzymes in the C4photosyntheticpathway, PEPC expressed specifically in C4plants leaves and could fix CO2.In this study, C4type PEPC gene was cloned from Zea mays B73and wasconnected with pCAMBIA3301H expression vector. We got90homozygous linesafter transfection, among them, there were37lines conformed to3:1. Thehomozygous lines with increased PEPC enzyme activity were obtained. The PEPCspecific enzyme activity in transgenic lines (including ZMOP0608, ZMOP3715, andZMOP7517) increased three to five times compared with wild type. The specificenzyme activity of the ZMOP0608was the highest among the homozygous lines.Under the condition of100ppm CO2, the phenotypes of ZMOP0608displayed greener leaves, more numbers of rosette leaves, higher fresh weight and specific leafweight compared with wild type. In the latter experiment, the transgenic lines whichhave high specific enzyme activity will be mutated to construct C4photosyntheticprototype.As a typical C4plant, Setaria viridis was used for correlational research on C4photosynthesis. With the increase of CO2concentration in the atmosphere in recentyears, more attention was paid on the effect of high CO2concentration on plants.Relevant research revealed that growth of plants would be restrained under thecondition of high CO2concentration, as was displayed in the C3plants like wheat,tomato and soybean. No reports are available based on the effect of the C4plants bysuper-elevated CO2concentration. In this study, the C4plant Setaria viridis wastreated with super-elevated CO2concentration (10000ppm). The Setaria viridisdisplayed yellowing leaves, nanoid plant and decreased dry and fresh weight incomparison with plants under normal condition. RNA of the third leaf was extractedand transcriptome analysis was performed. Based on the data of RNA-seq,174differentially expressed genes (DEGs) were detected under super-elevated CO2concentration compared with normal condition. Among them,100genes showedup-regulated and74genes revealed down-regulated. These DEGs were enriched forcarbohydrate metabolic process, light reaction of photosynthesis, oxidation-reduction process, stress response etc.14DEGs were found in the carbohydratemetabolic process, among them11genes showed up-regulated which include2kindsof cellulose synthase;6DEGs were found in light reaction of photosynthesis;27DEGs were found in oxidation-reduction process,13genes indicated down-regulated,NADPH oxidase played an important role under stress condition;25DEGs werefound in stress response, including related genes of light stress, bacterium stress，chemical stress. The sequence analysis could help revealing the respondingmechanism to the super-elevated CO2concentration by C4plants.