Stomata are pores on the plant surface that mediate water and gas exchange between plants and the atmosphere. The pattern of stomata in the epidermis layer of plants depends on cell–cell communication through positional cues, among them a family of secreted peptides called epidermal patterning factors (EPFs). Investigating the molecular mechanism of stomatal development and patterning, Keiko Torii and colleagues discovered an unexpected signalling mechanism. They find that two signalling peptides — Stomagen (a positive regulator of stomatal development) and EPF2 (a negative regulator of this process) — use the same receptor kinase, ERECTA, to fine-tune stomatal development. Intriguingly, both peptides bind to ERECTA and its co-receptor TMM with similar affinities, so they compete with each other for receptor binding. What seems to determine whether the activated ERECTA conveys a stimulatory or inhibitory signal is the downstream signalling: in vivo data show that EPF2, but not Stomagen, triggers phosphorylation of downstream signalling components.
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