Abstract
The two-dimensional pattern and density of stomata in the leaf epidermis are genetically and environmentally regulated to optimize gas exchange. Two putative intercellular signaling factors, EPF1 and EPF2, function as negative regulators of stomatal development in Arabidopsis, possibly by interacting with the receptor-like protein TMM. We discovered that a novel secretory peptide, which we designate as stomagen, is a positive intercellular signaling factor that is conserved among vascular plants. Stomagen is a 45-amino-acid, cysteine-rich peptide that is generated from a 102-amino-acid precursor protein designated as STOMAGEN. Both an in planta analysis and a semi-in-vitro analysis with recombinant and chemically synthesized stomagen peptides showed that stomagen has stomata-inducing activity in a dose-dependent manner. Our findings show that stomatal development is regulated by two classes of signals which have opposing effects: a positive signal, stomagen, and the negative signals, EPF1 and EPF2. Such a bidirectional signaling system would enable plants to control stomatal density more precisely.
