Abstract
A receptor kinase CLV1 and a secreted peptide CLV3, both of which are expressed in adjacent regions in the shoot apical meristem (SAM), are key components of the regulatory network controlling stem cell renewal and differentiation in Arabidopsis. Several lines of evidence suggest that the CLE domain, which is the only region with similarity among CLE family peptides, is the functional domain of CLV3. However, we have reservations about the proposed structure for the CLV3 functional form, mainly because exogenous application of the 12-amino-acid CLE domain peptide does not fully rescue clv3 mutant phenotypes at physiologically relevant concentrations. We thus assume that mature functional form of CLV3 may have undergone as-yet undiscovered posttranslational modifications critical for their function. Here, we show, by nano-LC-MS/MS analysis of apoplastic peptides of Arabidopsis plants overexpressing CLV3, that active mature CLV3 is a 13-amino-acid arabinosylated glycopeptide. We treated clv3-2 mutant seedlings with purified CLV3 glycopeptide and observed that the clv3-2 SAM treated with CLV3 at 30nM were substantially reduced in size comparable to wild-type levels. We also analyzed the binding affinity of CLV3 glycopeptide to CLV1 receptor kinase and confirmed that CLV3 glycopeptide interacted with the CLV1 ectodomain far more strongly than the non-arabinosylated forms. Collectively, we propose that active mature CLV3 is an arabinosylated glycopeptide.
