Comparative proteomics of Mesembryanthemum crystallinum guard cells and mesophyll cells in transition from C3 to CAM

Salinity can induce Mesembryanthemum crystallinum to shift its photosynthesis from C-3 to crassulacean acid metabolism (CAM), leading to enhanced plant water use efficiency. Studying how M. crystallinum changes its carbon fixation pathways is important for potential translation into crops and enhancing crop resilience. In this study, we examined proteomic changes in guard cells and mesophyll cells in the course of the C-3 to CAM transition. We collected enriched guard cells and mesophyll cells during a short period of transition. A total of 1153 proteins were identified and quantified in the two cell-types. During the transition, proteins in the guard cells and mesophyll cells exhibited differential changes. For example, we observed nocturnal carbon fixation in mesophyll cells and proteins involved in cell growth in the two cell-types. Proteins involved in osmotic adjustment, ion transport, energy metabolism and light response may play important roles in the C-3 to CAM transition. Real-time PCR experiments were conducted to determine potential correlations between transcript and protein levels. These results have highlighted potential molecular mechanisms underlying the C-3 to CAM transition of guard cells and mesophyll cells of the important facultative CAM plant. Biological significance: Fresh water resource for agricultural food production is a global challenge. Nature has evolved crassulacean acid metabolism (CAM) plants with enhanced water use efficiency. Using single cell-type proteomics, this study revealed molecular changes taking place in guard cells and mesophyll cells during the shift of ice plant photosynthesis from C-3 to CAM. The results have provided important insights into the CAM transition and may facilitate effort toward enhancing crop resilience for global food security.

Automated summary

This study investigated the proteomic changes in guard cells and mesophyll cells during the transition of ice plant photosynthesis from C-3 to CAM, revealing potential molecular mechanisms underlying the shift. These results provide important insights towards enhancing crop resilience and global food security.