Decoding the evolution of dumbbell stomata: Insights from the developmental genes of sedges and grasses

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) dumbbell-like stomata can be found. Dumbbell-like stomata in sedges share morphological features with grasses, suggesting potential conservation or convergence of developmental pathways. To investigate the evolution of dumbbell and dumbbell-like stomata, we analyzed genomic and transcriptomic data from 29 sedge species and five 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 is not present in both, and, in the ICE1/SCRM2 family, SCRM2 was lost while ICE1 was duplicated in sedges. Gene family expansion in grasses occurred primarily in genes involved in early stages of stomatal development, while the non-duplicated or independently expanded genes shared by sedges and grasses contribute to the development of the two lateral subsidiary cells as well as the guard cells. The gene conservation and independent expansion suggest shared regulatory networks underlying the stomata morphology typical of the order Poales. This study serves as an evolutionary guide for testing functional proteins underlying paracytic dumbbell and dumbbell-like stomata development.