Comparative analysis of thylakoid protein complexes in the mesophyll and bundle sheath cells from C3, C4 and C3-C4 Paniceae grasses

To better understand the coordination between dark and light reactions during the transition from C3 to C4 photosynthesis, we optimized a method for separating thylakoids from mesophyll (MC) and bundle sheath cells (BSC) across different plant species. We grew six Paniceae grasses including representatives from the C3, C3‐C4 and C4photosynthetic types and all three C4 biochemical subtypes (NADP‐ME, NAD‐ME and PEPCK) in addition to Zea mays under control conditions (1000 μmol quanta m‐2 s‐1 and 400 ppm of CO2). Proteomics analysis of thylakoids under native conditions, using BN‐PAGE followed by LC/MS, demonstrated the presence of subunits of all light‐reaction related complexes in all species and cell types. C4 NADP‐ME species showed a higher PSI/PSII ratio and a clear accumulation of NDH complexes in BSCs, while Cytb6f was more abundant in BSCs of C4 NAD‐ME species. The C4 PEPCK species showed no clear differences between cell types. Our study presents, for the first time, a good separation between BSC and MC for a C3‐C4 intermediate grass which did not show noticeable differences in the distribution of the thylakoid complexes. For the NADP‐ME species P. antidotale, growth at glacial CO2 (180 ppm of CO2) had no effect on the distribution of the light‐reaction complexes, while growth at low light (200 μmol quanta m‐2 s‐1) promoted the accumulation of light‐harvesting proteins in both cell types. These results add to our understanding of thylakoid distribution across photosynthetic types and subtypes, and introduce thylakoid distribution between the MC and BSC of a C3‐C4 intermediate species.