Evolutionary conserved sap peptides derived from xylem-specific peptide precursors in woody angiosperms

Abstract

Peptides act as long-distance mobile signals, transported through vascular sap to coordinate complex developmental processes. Since the tissue-specificity of peptide precursor gene expression is critical in determining peptide signaling function, we integrated vascular sap peptidomes with tissue-level transcriptomes to investigate the roles of sap peptides in two economically important woody plants, Populus trichocarpa and Eucalyptus grandis. Xylem exhibited the highest ratio of tissue-specific sap peptide precursor genes. Most of the sap peptides derived from xylem-specific precursor genes of P. trichocarpa and E. grandis were highly conserved throughout woody species selected from different clades in angiosperms, including magnoliids, rosids and asterids in eudicots. To further explore the conservation of these peptides, we examined the sap peptidome of Cinnamomum kanehirae (camphor tree), from the ancient clade with three xylem cell types. Approximately 90% of the peptides from xylem-specific precursors that were conserved between P. trichocarpa and E. grandis, were also conserved in the vascular sap of C. kanehirae, demonstrating a remarkably high conservation of these peptides across woody angiosperms. Most of the sap peptides conserved in these three woody species are also highly conserved across land plants, suggesting that these peptides may contribute to plant terrestrialization. Within the sap peptides from xylem- specific precursor genes, a total of 10 peptides were identical across all three woody plants. This substantial enrichment of xylem-specific precursor-derived peptides, along with their high conservation, suggests that these long-distance mobile peptides play a crucial role in secondary xylem development.