Plant physiology depends on stomata, pores in the leaf epidermis that permit gas exchange and regulate water levels. Stomatal patterning is regulated by signalling peptides that can act antagonistically and both within and between cell layers, ensuring, for example, that no two stomata differentiate next to one another. However, the details of how these peptides move between cells to regulate stomatal placement has been hard to study. Keiko Torii and colleagues now use a combination of Cre-lox and GAL4/UAS systems to restrict peptide overexpression to localised (and GFP-labelled) sectors of the developing leaf. Within sectors, the peptides EPF1 and STOMAGEN respectively inhibit and promote stomatal development, as expected. They also act non-cell autonomously on adjacent tissue, and between layers when expressed only in mesophyll sectors. To quantitatively analyse the effective ranges of the peptides, the authors adapt a statistical approach based on spatial correlation that astrophysicists use to predict galaxy distributions. This SPACE pipeline reveals that the range of EPF1 is larger than STOMAGEN (over 100µm compared to ∼60µm), and indicates that local manipulation of signalling does not feed in to the previously described global stomatal patterning processes. As well as providing new insights into the mechanisms of stomatal signalling, the SPACE pipeline promises to be applicable to many developmental patterning problems.
