Comparative genomics can provide new insights into the evolutionary mechanisms and gene function in CAM plants

Abstract

Crassulacean acid metabolism (CAM) photosynthesis is an important biological innovation enabling plant adaptation to hot and dry environments. CAM plants feature high water-use efficiency, with potential for sustainable crop production under water-limited conditions. A deep understanding of CAM-related gene function and molecular evolution of CAM plants is critical for exploiting the potential of engineering CAM into C3 crops to enhance crop production on semi-arid or marginal agricultural lands. With the newly emerging genomics resources for multiple CAM species, progress has been made in comparative genomics studies on the molecular basis and subsequently on the evolution of CAM. Here, recent advances in CAM comparative genomics research in constitutive and facultative CAM plants are reviewed, with a focus on the analyses of DNA/protein sequences and gene expression to provide new insights into the path and driving force of CAM evolution and to identify candidate genes involved in CAM-related biological processes. Potential applications of new computational and experimental technologies (e.g. CRISPR/Cas-mediated genome-editing technology) to the comparative and evolutionary genomics research on CAM plants are offered.

Keywords: Comparative genomics; crassulacean acid metabolism; drought stress; evolution; gene function; genome editing; photosynthesis.

Fig. 1.

A conceptual framework for crassulacean acid metabolism (CAM) evolution and working hypotheses for guiding comparative genomics research. (A) Hypothesis (i): CAM evolution followed a linear course leading from facultative CAM to strong constitutive CAM. (B) Hypothesis (ii): facultative and constitutive CAM evolved independently.

Fig. 2.

A comparative genomics framework for elucidating gene function associated with crassulacean acid metabolism (CAM). This framework integrates the ontogenetic C₃-to-CAM transition in constitutive CAM species, environmental induction/up-regulation of CAM expression in facultative CAM species, and differences between CAM and non-CAM species.