Subtilase-mediated activation of CLEL peptides involves several processing events in consecutive compartments of the secretory pathway
AbstractSmall post-translationally modified peptides are emerging as a novel class of signaling molecules that are involved in many aspects of plant growth and development, and in the interaction of plants with their biotic environment. Despite considerable progress with respect to the receptor-mediated perception and signal transduction mechanisms, the maturation of these peptides from their larger precursors is still poorly understood. This question was addressed here for CLEL6 and CLEL9
... LEL6 and CLEL9 (also known as GOLVEN 1 and 2) that are known to control gravitropic responses of the shoot and the root by modulation auxin distribution.Several proteolytic processing events located in consecutive compartments of the secretory pathway were found to be required for the formation of bioactive CLEL peptides. Using an inhibitor-based approach for loss-of-function analysis, targeting protease function at the level of enzyme activity rather than gene expression, we show that the step-wise maturation of CLEL peptides is mediated by subtilases (SBTs). Following the cleavage of the signal peptide upon entry into the ER, the CLEL6 and 9 precursors are processed at two sites in their variable domain by SBT6.1. Cleavage by SBT6.1 in the cis-Golgi allows for continued passage of the partially processed (pre-activated) precursors through the secretory pathway, and is thus a prerequisite for subsequent post-translational modifications including tyrosine sulfation and proline hydroxylation within the Golgi, and proteolytic maturation after exit from the Golgi. The activation of CLEL6 and CLEL9 by SBTs in the trans-Golgi network or other post-Golgi compartments depends on the N-terminal aspartate of the mature peptides.