More Than Meets The Eye: Knowns And Unknowns Of The Trafficking Of Small Secreted Proteins In Arabidopsis.

Small proteins represent a significant portion of the cargo transported through plant secretory pathways, playing crucial roles in developmental processes, fertilization, and responses to environmental stresses. Despite their importance, substantial knowledge gaps persist regarding the regulatory mechanisms governing their trafficking along the secretory pathway, and ultimate localization/destination. To address these gaps, we conducted a comprehensive literature review, focusing particularly on trafficking and localization of small secreted proteins with potential biochemical and/or signaling roles in the extracellular space, typically within the size range of 101-200 amino acids. Our investigation reveals that while at least 6 members of the 21 mentioned families confirm extracellular localization, 8 of them exhibit intracellular localization (including cytoplasmic, nuclear, and chloroplastic locations, despite the presence of N-terminal signal peptides). Further investigation into the trafficking and secretion mechanisms of small protein cargo could not only deepen our understanding of plant cell biology and physiology but also provide a foundation for manipulation strategies leading to more efficient plant cultivation.