Correlation Study On CO₂ Utilization Efficiency Of Transgenic Rice With IctB Gene

The formation of crop yield directly or indirectly comes from the accumulation of photosynthetic products,and it has great potential to increase rice yield by improving the utilization rate of light energy.Some algae cells have efficient inorganic carbon transport system and concentration mechanism,which can enrich low-concentration CO₂ in the external environment to the active site of RuBisCo,improve its photosynthetic efficiency and reduce the photorespiration rate.It is of profound significance to improve photosynthetic characteristics of rice by utilizing high-efficient CO₂ concentration genes of high-photosynthetic species such as cyanobacteria.In this study,physiological and biochemical indicators related to photosynthetic characteristics of rice transgenic with ictB gene were analysed.This study explored the effect of ictB on the photosynthetic limiting factors of rice,and laid a theoretical foundation for improving the photosynthetic efficiency of rice by using ictB gene.The main research results are as follows:?1?The ictB transgenic rice was detected positive by PCR.The transgenic material can efficiently express the target gene through RT-PCR and qPCR detection.Molecular detection of transgenic rice showed that the ictB gene of transgenic lines could be stably inherited and expressed.?2?Photosynthetic indices of rice flag leaves at tillering stage and filling stage were determined by Li-6400 photosynthetic instrument,and the results showed that the photosynthetic rates of the transgenic lines at tillering stage were increased by0.4%and 2.2%respectively,and the intercellular CO₂ concentration was decreased by11.54%and 1.5%,respectively.During the filling period,the photosynthetic rates of transgenic lines increased by 11.74%and 4.1%,and the intercellular CO₂concentration decreased by 8.8%and 6.7%,respectively.The results showed that the expression of ictB gene significantly promoted the transport efficiency of inorganic carbon,significantly reduced the intercellular CO₂ concentration,and increased the net photosynthetic rate.?3?The light response curve fitting analysis of transgenic lines and their control showed that the light saturation points of transgenic lines ictB-1 and ictB-2 were 2251mol·m^-2·s^-11 and 2903 mol·m^-2·s^-1,respectively,compared with 1501 mol·m^-2·s^-11 in the control group.Results showed that the photosynthetic system could withstand the strong light and the light saturation point increased.?4?The CO₂ response curve fitting analysis of transgenic lines and their controls showed that the CO₂ compensation points of transgenic lines ictB-1 and ictB-2 were lower than those of the control lines.CO₂ compensation points of transgenic lines were 88.58 ppm and 79.14 ppm,respectively,which were 8.76%and18.64%lower than those of the control group?97.27 ppm?.This showed that the expression of ictB gene could promote the transport of more inorganic carbon to the RuBisCo reaction center,reduce the CO₂ compensation point of the transgenic material,and increase the photosynthetic activity of its RuBisCo.The photosynthetic ability of the transgenic material was considerably enhanced under the condition of low CO₂ concentration.?5?Li-6400 photosynthetic instrument and CCIA were used to measure the mesophyll conductance.Transgenic lines at 300ppm and 400ppm CO₂ concentrations were extremely significantly higher than that of the control,and there was no significant difference between the transgenic lines and the control at 500ppm CO₂concentrations.The results showed that the expression of ictB gene could enhance the transport of inorganic carbon,reduce the resistance of inorganic carbon transport,and increase the CO₂ mesophyll conductance of the leaves under low CO₂ concentration.?6?Liquid chromatography-mass spectrometry?LC-MS?was used to determine the metabolites related to the photosynthetic pathway in rice,and it was found that the content of photorespiratory metabolic markers?PGlyco and Hypr?in transgenic lines was significantly decreased,the metabolic flow of Calvin cycle was significantly increased,and the content of Sucrose and ADPG in the products of the sugar metabolic pathway was also increased.It showed that the enhanced ability of inorganic carbon transport in transgenic lines could significantly enhance the carboxylation activity of RuBisCo and inhibit its oxygenation activity;RuBP regeneration rate and Calvin cycle reaction rate were accelerated;the CO₂ utilization efficiency of rice transgenic with ictB gene was improved,and photorespiration was inhibited.