Insights from the developmental genes of sedges and grasses

The evolution of stomatal morphology is a defining trait among plant lineages. Grasses (Poaceae) have distinctive dumbbell-shaped stomata that enhance water-use efficiency compared to the more common kidney-shaped stomata. In the closely related sedges (Cyperaceae), both kidney-shaped and dumbbell-like stomata can be found. Dumbbell-like stomata in sedges share morphological features with grasses, suggesting potential conservation of developmental pathways. To investigate the evolution of dumbbell and dumbbell-like stomata, we analyzed genomic and transcriptomic data from 29 sedge species and 5 grass species. Using their predicted proteomes, we identified orthologues involved in stomatal development and reconstructed their phylogenetic histories. Among the 16 gene families analyzed, EPFL9, YODA, SCR, and SHR were expanded in grasses but not in sedges. POLAR, SPCH, and ABI were expanded in both lineages, seven families were conserved in both, BASL was lost in both, and, in the SCRM/ICE family, SCRM was lost while ICE was duplicated in sedges. Gene family expansion in grasses occurred primarily in genes involved in early stages of stomatal development, while gene families non-duplicated or independently expanded act in later stages. The non-duplicated or independently expanded genes shared by sedges and grasses contribute to development of the two lateral subsidiary cells as well as the guard cells, suggesting shared regulatory networks underlying the stomata morphology typical of the order Poales. Our study provides a crucial guide to further test functional proteins underlying paracytic dumbbell-like stomata development.