Integrative analysis of CAM photosynthesis reveals its impact on primary metabolism in Yucca

Crassulacean Acid Metabolism (CAM) is an adaptation that temporally separates carbon uptake at night from photosynthesis during the day. CAM has evolved repeatedly across vascular plants, perhaps, in part, because it does not involve any novel gene functions and instead relies on regulatory modification of existing C ₃ pathways. The co-option of established processes and corresponding alteration of metabolic flux is likely to impact other primary metabolic pathways such as nitrogen metabolism and photorespiration. However, the majority of CAM research to date has focused on a handful of genes in the core CAM pathway. Understanding the complex downstream effects associated with the emergence of CAM is essential to explaining its convergent evolution as well as efforts to engineer carbon concentrating mechanisms in crops. In this study, we integrate genomic, transcriptomic, proteomic, and metabolomic data to compare primary metabolism between the CAM species Yucca aloifolia and closely related C ₃ species, Y. filamentosa . Despite substantial differences in metabolite abundance across multiple pathways, including citrate and nitrogen metabolism, we observe relatively few gene expression differences outside of the core CAM pathway. Additionally, we observe minimal correlation between protein abundance and mRNA expression, suggesting significant post-transcriptional regulation in CAM species. Our findings provide insights into the metabolic shifts associated with CAM evolution and highlight the complexity of its regulation at multiple biological levels.