| Summary: | The Arabidopsis <i>PROSCOOP</i> genes belong to a family predicted to encode secreted pro-peptides, which undergo maturation steps to produce peptides named SCOOP. Some of them are involved in defence signalling through their perception by a receptor complex including MIK2, BAK1 and BKK1. Here, we focused on the <i>PROSCOOP10</i> gene, which is highly and constitutively expressed in aerial organs. The MS/MS analyses of leaf apoplastic fluids allowed the identification of two distinct peptides (named SCOOP10#1 and SCOOP10#2) covering two different regions of PROSCOOP10. They both possess the canonical S-X-S family motif and have hydroxylated prolines. This identification in apoplastic fluids confirms the biological reality of SCOOP peptides for the first time. NMR and molecular dynamics studies showed that the SCOOP10 peptides, although largely unstructured in solution, tend to assume a hairpin-like fold, exposing the two serine residues previously identified as essential for the peptide activity. Furthermore, <i>PROSCOOP10</i> mutations led to an early-flowering phenotype and increased expression of the floral integrators <i>SOC1</i> and <i>LEAFY</i>, consistent with the de-regulated transcription of <i>PROSCOOP10</i> in several other mutants displaying early- or late-flowering phenotypes. These results suggest a role for <i>PROSCOOP10</i> in flowering time, highlighting the functional diversity within the <i>PROSCOOP</i> family.
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