Abstract
Stomagen is a cysteine rich peptide that induces stomatal differentiation. Cysteine rich peptides are involved in various processes in plant life: LUREs regulate a pollen tube guidance in Torenia fournieri and NRCs regulate the rhizobium-plant symbiosis in Medicago truncatula.
A physiological function of stomagen is the opposite of that of EPF2, although these peptides belong to the same EPF family. EPF2 overexpression reduced the number of stomata. A similar reduction of stomatal density was observed by an application of recombinant EPF2. We investigated how the physiological difference between stomagen and EPF2 is caused. Replacement of all six cysteine residues by serine made stomagen have no activity, suggesting that the tertiary structure supported by the S-S bonds is important to the function of stomagen. EPF2 has eight cysteines, six of which are conserved in stomagen. We hypothesized the amino-acid sequence that contains EPF2 specific cysteines is responsible for the functional difference between stomagen and EPF2. Domain swapping experiment supported the hypothesis, that is, the stomagen specific sequence gave EPF2 a stomata inducing activity.
