A subtilisin-like serine protease involved in the regulation of stomatal density and distribution in Arabidopsis thaliana

Stomata are specialized cellular structures in the epidermis of aerial plan t organs that control gas exchange (H2O release and CO2 uptake) between lea ves and the atmosphere by modulating the aperture of a pore flanked by two guard cells. Stomata are nonrandomly distributed, and their density is cont rolled by endogenous and environmental factors. To gain insight into the mo lecular mechanisms regulating stomatal distribution, Arabidopsis thaliana m utants with altered stomatal characteristics were isolated and examined. Th e sdd1-1 mutant exhibits a two- to fourfold increase of stomatal density an d formation of clustered stomata (i.e., stomata that are not separated by i ntervening pavement cells), whereas the internal leaf architecture is not a ltered. The SDD1 gene was identified by map-based cloning. It encodes a sub tilisin-like serine protease related to prokaryotic and eukaryotic proteins . We propose that SDD1 acts as a processing protease involved in the mediat ion of a signal that controls the development of cell lineages that lead to guard cell formation.