Plant twitter: ligands under 140 amino acids enforcing stomatal patterning

Abstract

Stomata are an essential land plant innovation whose patterning and density are under genetic and environmental control. Recently, several putative ligands have been discovered that influence stomatal density, and they all belong to the epidermal patterning factor-like family of secreted cysteine-rich peptides. Two of these putative ligands, EPF1 and EPF2, are expressed exclusively in the stomatal lineage cells and negatively regulate stomatal density. A third, EPFL6 or CHALLAH, is also a negative regulator of density, but is expressed subepidermally in the hypocotyl. A fourth, EPFL9 or STOMAGEN, is expressed in the mesophyll tissues and is a positive regulator of density. Genetic evidence suggests that these ligands may compete for the same receptor complex. Proper stomatal patterning is likely to be an intricate process involving ligand competition, regional specificity, and communication between tissue layers. EPFL-family genes exist in the moss Physcomitrella patens, the lycophyte Selaginella moellendorffii, and rice, Oryza sativa, and their sequence analysis yields several genes some of which are related to EPF1, EPF2, EPFL6, and EPFL9. Presence of these EPFL family members in the basal land plants suggests an exciting hypothesis that the genetic components for stomatal patterning originated early in land plant evolution.

Stomatal Development in Arabidopsis

“…These cysteine linkages expose a variable loop domain believed to be the major source of the biochemical and functional diversity among family members (Ohki et al, 2011) (Figure 7). The EPF protein family (EPFf) is made up of 11 members (EPF1, EPF2 and EPFL1-9) that participate in diverse developmental processes (Hara et al, 2007;Hara et al, 2009;Hunt and Gray, 2009;Rowe and Bergmann, 2010;Rychel et al, 2010;Torii, 2012). STOMAGEN (EPFL9: At4g12970) has been experimentally shown to be post-translationally modified and it is likely that the other members are similarly processed (Kondo et al, 2009;Ohki et al, 2011).…”

Auxin represses stomatal development in dark-grown seedlings via Aux/IAA proteins

“…In cotyledons and leaves, it restricts stomata differentiation and guides spacing divisions in concert with the ERf, but in hypocotyls and stems, it promotes stomatal development and thereby antagonises ERf function (Bhave et al, 2009;Nadeau and Sack, 2002;Shpak et al, 2005;Yang and Sack, 1995). Activity of the TMM-ERf module is controlled by cysteinerich peptide ligands of the EPIDERMAL PATTERNING FACTOR-LIKE (EPFL) family (Lee et al, 2012;Rychel et al, 2010).…”

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

“…In plants, this signaling is often mediated by leucine-rich repeat, single transmembrane pass receptor-like kinases (LRR-RLKs; Shiu and Bleecker, 2001). Putative peptide ligands for these LRR-RLKs are structurally diverse, ranging in size from modified pentapeptides to small (50 to 100 amino acids long) proteins and are often part of large gene families (reviewed in Butenko et al, 2009;Jun et al, 2010;Rowe and Bergmann, 2010;Rychel et al, 2010). The roles and receptor interactions of these putative ligands remain largely unknown, as do the mechanisms that enable related ligands to function in distinct processes and interact with different receptors.…”