Enhanced drought tolerance and photosynthetic efficiency in Arabidopsis by overexpressing phosphoenolpyruvate carboxylase from a single-cell C4 halophyte Suaeda aralocaspica

In crop genetic improvement, the introduction of C4 plants' characteristics, known for high photosynthetic efficiency and water utilization, into C3 plants has been a significant challenge. This study investigates the effects of the desert halophyte <i>Suaeda aralocaspica SaPEPC1</i> gene from a single-cell C4 photosythetic pathway, on drought resistance and photosynthetic performance in <i>Arabidopsis</i>. We used transgenic <i>Arabidopsis</i> with <i>Zea mays ZmPEPC1</i> from C4 plant with classic Kranz anatomical structure and <i>Arabidopsis AtPEPC1</i> from C3 photosynthetic cycle plants as controls. The results demonstrated that C4 photosynthetic-type <i>PEPCs</i> could improve drought resistance in plants through stomatal closure, promoting antioxidant enzyme accumulation, and reducing reactive oxygen species (ROS) accumulation. Overexpression of <i>SaPEPC1</i> was significantly more effective than <i>ZmPEPC1</i> in enhancing drought tolerance. Notably, overexpressed <i>SaPEPC1</i> significantly improved light saturation intensity, electron transport rate (ETR), photosynthetic rate (Pn), and photoprotection ability under intense light. Furthermore, overexpression <i>SaPEPC1</i> or <i>ZmPEPC1</i> enhanced the activity of key C4 photosynthetic enzymes, including phosphoenolpyruvate carboxylase (PEPC), pyruvate orthophosphate dikinase (PPDK) and NADP-malic enzyme (NADP-ME), and promoted photosynthetic product sugar accumulation. However, with <i>AtPEPC1</i> overexpression showing no obvious improvement effect on drought and photosynthetic performance. Therefore, these results indicated that introducing C4-type <i>PEPC</i> into C3 plants can significantly enhance drought resistance and photosynthetic performance. However, <i>SaPEPC1</i> from a single-cell C4 cycle plant exhibits more significant effect in ETR and PSII photosynthesis performance than <i>ZmPEPC1</i> from a classical C4 anatomical structure plant, although the underlying mechanism requires further exploration.