Study Of C₃ To CAM Transition Induced By Salt Of Facultative CAM Plant M.crystallinum Using System Biology

Salt stress impedes plant growth and development and leads to yield loss.Mesembryanthemum crystallinum is a facultative CAM plant,which can switch its photosynthesis from C3 to CAM under salt stress.CAM plants have high water use efficiency,their stomata open in the night to reduce diurnal water lose and allow for CO2 uptake.A phosphoenolpyruvate carboxylase(PEPC)catalyzes the fixation of atmospheric CO2 resulting in the accumulation of malate in large vacuoles.During daylight hours,stomata are closed and water transpiration is reduced.CO2 is released from malate fixed in the night,and is then utilized in the Calvin-Benson cycle for sugar production.Therefore,by studying the C3 to CAM transitoin period,we were able to investigate mechanistic changes of photosynthesis,especially the regulatory triggers in facultative CAM plants,and a potential solution for increasing crop salt tolerance.The main contents and results of this paper are as follows:(1)Physiological changes in M.crystallinum during the C3 to CAM transition induced by salt stressM.crystallinum is a module CAM plant with published researches showing the differences between the CAM and C3 photosynthesis.In this study,we focused on investigating the morphology and physiology of M.crystallinum during and the transition under salt stress,specifically the changes of stomata behavior including microscopic observation and gas exchange measurement.Our results showed that in mature M.crystallinum,CAM was involved after few days of salt treatment and took control of photosynthesis in two weeks.This result indicated the high efficiency of the transition and the model salt response for facultative CAM plants.(2)Comparative proteomics of M.crystallinum guard cells and mesophyll cells in the transition from C3 to CAMCAM was determined happened in mesophyll cells,but stomata guard cells have morphological change during the C3 to CAM transition,whether guard cells are involved in the C3 to CAM transition remains unknown.In this study,we examined how guard cells and mesophyll cells are involved in the C3 to CAM transition using proteomics platform.A total of 1,153 proteins were identified and quantified in both cell-types.Our results showed that guard cells and mesophyll cells had different protein abundances.Protein associated with guard cells and mesophyll cells responded differently to the salt stress.These results have provided interesting insight into the roles of guard cells and mesophyll cells during the C3 to CAM transition in the important facultative CAM plant.(3)Multi-omics of M.crystallinum leaf in the transition from C3 to CAMM.crystallinum leaves can change their photosynthesis from C3 to CAM under salt stress in a short period.However how this changing is triggered remains unknown.To identify the molecular switches responsible for the transition from C3 to CAM,we used multi-omics platform to exam the molecular changes in leaf during the transition,including transcriptomics,proteomics and metabolomics.A total of 26,053 transcripts,1,588 proteins and 1,071 metabolites were quantified during the transition.Our results showing the transcripts and proteins involved in transmembrane transport,ion binding and methylation were up-regulated/increased during the transition,the metabolites involved in carbon fixation and TCA cycle had significant change during the transition.Interestingly,inositol methyltransferase was highly up-regulated/increased during the transition.These results have provided a comprehensive insight in RNA,protein and metabolite level in M.crystallinum during the C3 to CAM transition.