Gene duplications facilitate C4-CAM compatibility in common purslane

Area of Science:

• Plant biology
• Genomics
• Photosynthesis research

Background:

• Common purslane (Portulaca oleracea) uniquely combines C4 and crassulacean acid metabolism (CAM) photosynthesis.
• This plasticity makes it a valuable model for studying C4-CAM integration.

Purpose of the Study:

• To generate a high-quality genome assembly for common purslane.
• To investigate the evolutionary history of C4 and CAM pathways in this species.
• To identify genetic mechanisms underlying C4-CAM plasticity.

Main Methods:

• Chromosome-level genome sequencing and assembly.
• Phylogenetic analysis and whole-genome duplication (WGD) dating.
• Gene copy number variation analysis.
• Analysis of cis-regulatory elements in gene promoters.

Main Results:

• A high-quality genome of NAD-malic enzyme (ME) subtype common purslane was produced.
• Evidence for two WGD events: an ancient P-β (66.30 Mya) and a lineage-specific Po-α (7.74 Mya).
• Po-α WGD generated phosphoenolpyruvate carboxylase gene copies for C4 photosynthesis.
• P-β WGD produced ancestral genes for functionally differentiated beta carbonic anhydrases (C4- and CAM-specific).
• CAM-specific genes recruited circadian and ethylene-response factor cis-elements.

Conclusions:

• The study elucidates the evolutionary origins of C4 and CAM pathways in common purslane.
• WGD events played a crucial role in expanding gene families for photosynthesis.
• Identified regulatory elements provide targets for engineering C4 or CAM metabolism in crops.