Post-translational maturation of IDA, a peptide signal controlling floral organ abscission in Arabidopsis

Abstract

The abscission of sepals, petals and stamens in Arabidopsis flowers is controlled by a peptide signal called IDA (Inflorescence Deficient in Abscission). IDA belongs to the large group of small post-translationally modified signaling peptides that are synthesized as larger precursors and require proteolytic processing and specific side chain modifications for signal biogenesis. Using tissue-specific expression of proteinase inhibitors as a novel approach for loss-of-function analysis, we recently identified the peptidases responsible for IDA maturation within the large family of subtilisin-like proteinases (subtilases; SBTs). Further biochemical and physiological assays identified three SBTs (AtSBT5.2, AtSBT4.12, AtSBT4.13) that cleave the IDA precursor to generate the N-terminus of the mature peptide. The C-terminal processing enzyme(s) remain(s) to be identified. While proline hydroxylation was suggested as additional post-translational modification required for IDA maturation, hydroxylated and non-hydroxylated IDA peptides were found to be equally active in bioassays for abscission.

Regulation of plant peptide hormones and growth factors by post‐translational modification

“…Surprisingly, however, the abscission‐inducing activity of IDA was indistinguishable for the hydroxylated and non‐hydroxylated forms of the mature peptide (Stührwohldt et al . ). In order to explain this obvious discrepancy, we speculate that mIDA may become hydroxylated after being taken up by the plant.…”

Differential expression of IDA (INFLORESCENCE DEFICIENT IN ABSCISSION)-like genes in Nicotiana benthamiana during corolla abscission, stem growth and water stress

“…The presence of this signal peptide in the sequence of all identified genes suggests a mechanism of posttranslational maturation in the apoplast similar to that described in Arabidopsis, where the prepropeptide is proteolytically processed by subtilisin-like serine proteinases to yield a bioactive peptide [29]. This cleavage that occurs between positions 6 and 7 of the EPIP motif [30], normally occupied by a K and a G respectively, leaves a bioactive peptide of 14 amino acids containing the PIP motif with G7 as N-terminal and N20 as C-terminal residues (Figure 2).…”

The root-knot nematode Meloidogyne incognita produces a functional mimic of the Arabidopsis INFLORESCENCE DEFICIENT IN ABSCISSION signaling peptide

“…The Arabidopsis IDA precursor protein is secreted into the apoplast where it is processed into a smaller peptide ( Stenvik et al , 2008 b ; Butenko and Simon, 2015 ; Schardon et al , 2016 ). The secreted IDA protein is predicted to be cleaved by subtilisin-like serine proteinases at both the N-terminus and C-terminus resulting in a 14 amino acid bioactive product (GVPIPPSAPSKRHN) ( Schardon et al , 2016 ; Stührwohldt et al , 2017 ). When the N-terminal cleavage site was blocked with N-methylation of the Lys/Gly bond in a longer 23 amino acid peptide (SHIFGYLPK[m]GVPIPPSAPSKRHN), the methylated peptide was completely inactive whereas the non-methylated 23 amino acid peptide retained activity.…”

“…In addition, others have demonstrated that the ida mutant phenotype could be rescued with IDA-like peptides that do not contain a hydroxyproline modification ( Stenvik et al , 2008 b ; Schardon et al , 2016 ). Interestingly, a recent report argues that the exogenously applied peptides might still be hydroxylated at proline by an extracellular enzyme ( Stührwohldt et al , 2017 ).…”