Metabolic flexibility in drought: Leveraging Portulaca for defining design principles for a combined C4-CAM pathway

Introduction

Rising heatwaves and drought are severely affecting the capacity of crops to retain water and capture CO2 during photosynthesis, resulting in global yield reductions. One of the most promising approaches to enhance crop production in stressful conditions is to synthetically modify the photosynthetic capacity of plants.

Natural Mechanisms

In nature, some lineages have evolved mechanisms like:

• C4 photosynthesis
• Crassulacean acid metabolism (CAM)

These adaptations help cope with environmental stress. While C4 species are extremely efficient at CO2 fixation, they are vulnerable to severe drought. On the other hand, CAM plants are less productive but very capable of coping with significant drought periods.

Engineering a Solution

Engineering a joint C4-CAM system that utilizes CAM features to combat drought, while still leveraging the efficiency of C4, can be a game-changer for increasing crop resilience. For decades, the coexistence of C4 and CAM was considered incompatible in nature.

Exception in Nature

An exception to this rule is found in the genus Portulaca, where C4 species can trigger CAM when droughted. Despite the huge bioengineering potential of Portulaca, the molecular enablers that allow for C4-CAM to exist in this clade remain elusive.

Research Background

Previous phylogenetic and morphological studies across Portulaca indicate that the combined C4 (Kranz anatomy) and CAM (succulence) leaf anatomy might be the main facilitator of C4-CAM.

Research Objectives

By combining anatomical studies, cell-specific metabolomics, and genomics with synthetic biology, I aim to:

1. Identify the basic molecular determinants of the C4-CAM switch in Portulaca.
2. Leverage this knowledge to transfer CAM anatomical features to C4 species outside Portulaca as a proof of principle.

Future Implications

This will set the basis for new rounds of engineering to achieve a fully functional C4-CAM switch. METACAM will provide a quantum leap in our understanding of how incompatible metabolic pathways can be designed, built, and integrated in multicellular organisms, which is broadly applicable to crop engineering.