Overexpression of an Agave Phosphoenolpyruvate Carboxylase Improves Plant Growth and Stress Tolerance

Abstract

It has been challenging to simultaneously improve photosynthesis and stress tolerance in plants. Crassulacean acid metabolism (CAM) is a CO₂-concentrating mechanism that facilitates plant adaptation to water-limited environments. We hypothesized that the ectopic expression of a CAM-specific phospho<i>enol</i>pyruvate carboxylase (PEPC), an enzyme that catalyzes primary CO₂ fixation in CAM plants, would enhance both photosynthesis and abiotic stress tolerance. To test this hypothesis, we engineered a CAM-specific <i>PEPC</i> gene (named <i>AaPEPC1</i>) from <i>Agave americana</i> into tobacco. In comparison with wild-type and empty vector controls, transgenic tobacco plants constitutively expressing <i>AaPEPC1</i> showed a higher photosynthetic rate and biomass production under normal conditions, along with significant carbon metabolism changes in malate accumulation, the carbon isotope ratio δ¹³C, and the expression of multiple orthologs of CAM-related genes. Furthermore, <i>AaPEPC1</i> overexpression enhanced proline biosynthesis, and improved salt and drought tolerance in the transgenic plants. Under salt and drought stress conditions, the dry weight of transgenic tobacco plants overexpressing <i>AaPEPC1</i> was increased by up to 81.8% and 37.2%, respectively, in comparison with wild-type plants. Our findings open a new door to the simultaneous improvement of photosynthesis and stress tolerance in plants.