Stomagen positively regulates stomatal density in Arabidopsis

Abstract

Stomata in the epidermal tissues of leaves are valves through which passes CO(2), and as such they influence the global carbon cycle. The two-dimensional pattern and density of stomata in the leaf epidermis are genetically and environmentally regulated to optimize gas exchange. Two putative intercellular signalling factors, EPF1 and EPF2, function as negative regulators of stomatal development in Arabidopsis, possibly by interacting with the receptor-like protein TMM. One or more positive intercellular signalling factors are assumed to be involved in stomatal development, but their identities are unknown. Here we show that a novel secretory peptide, which we designate as stomagen, is a positive intercellular signalling factor that is conserved among vascular plants. Stomagen is a 45-amino-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. A genetic analysis showed that TMM is epistatic to STOMAGEN (At4g12970), suggesting that stomatal development is finely regulated by competitive binding of positive and negative regulators to the same receptor. Notably, STOMAGEN is expressed in inner tissues (the mesophyll) of immature leaves but not in the epidermal tissues where stomata develop. This study provides evidence of a mesophyll-derived positive regulator of stomatal density. Our findings provide a conceptual advancement in understanding stomatal development: inner photosynthetic tissues optimize their function by regulating stomatal density in the epidermis for efficient uptake of CO(2).

The NMR structure of stomagen reveals the basis of stomatal density regulation by plant peptide hormones

“…The functions of the other members remain unclear. Interestingly, it is currently known that stomagen (EPFL9) acts as a positive regulator [10][11][12] . One of the most intriguing questions in this area is how and why peptides from the same family can produce opposite effects on stomatal density.…”

Generation of Signaling Specificity in Arabidopsis by Spatially Restricted Buffering of Ligand–Receptor Interactions

“…The EPFLs are small proteins predicted (and in one case, demonstrated) to be processed into ;45-to 75-amino acid long secreted peptides with compact Cys knot structures (Kondo et al, 2009;Sugano et al, 2009). Three members of the gene family, EPF1, EPF2, and EPFL9/STOMAGEN, have clear roles in stomatal development.…”

A Tale of Two Systems: Peptide Ligand-Receptor Pairs in Plant Development

“…Although the interaction between EPFL9/Stomagen and ERECTA-family kinases has not yet been tested, genetic evidence also suggests that EPFL9/Stomagen (a positive regulator) might compete in binding for the same receptors with EPF2 (a negative regulator) during stomatal development (Sugano et al 2010). It is thus possible that different tissue distribution of each EPF gene expression is also an important factor in determining the specificity of EPF function through broadly expressed ERECTA-family receptors.…”

“…Subsequent bioinformatic approaches identified several EPF1 homologs, all of which code for secreted cysteine-rich peptide (Hara et al 2009;Hunt and Gray 2009;Sugano et al 2010;Matsubayashi 2011). There are 11 EPF family members in Arabidopsis and they all have a characteristic, carboxy-terminal domain containing six or eight cysteine residues that are essential for the formation of intramolecular disulfide bonds (Rychel et al 2010).…”