The PROSCOOP10 gene encodes two extracellular hydroxylated peptides and impacts flowering time in Arabidopsis

Abstract

The Arabidopsis PROSCOOP 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 PROSCOOP10 gene which is highly and constitutively expressed in the 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 for the first time the biological reality of SCOOP peptides. 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, PROSCOOP10 mutations led to an early flowering phenotype and an increased expression of the floral integrators SOC1 and LEAFY, consistent with the transcription of PROSCOOP10 in several mutants displaying an early or late flowering phenotype. These results suggest a role of PROSCOOP10 in flowering time, illustrating the functional complexity of the PROSCOOP family.