Time-based LC-MS/MS analysis provides insights into early responses to mechanical wounding, a major trigger to agarwood formation in Aquilaria malaccensis Lam

Abstract

Mechanical wounding is the major trigger for the formation of agarwood in the tropical tree taxon Aquilaria. To understand the molecular mechanism by which Aquilaria reacts to wounding, we applied a proteomics approach using liquid chromatography electrospray-ionization coupled with tandem mass spectrometry (LC-MS/MS) coupled with bioinformatics analysis and principal component analysis. Protein samples were extracted from wood tissues collected from drilled wounds on the stems of five-year old Aquilaria malaccensis. Samples were collected at different time-points of 0, 2, 6, 12, and 24 h after mechanical wounding for protein identification. Venn diagram analysis showed that 564 out of 2227 identified proteins were time-point specific proteins. GO analysis using the REViGO software (including functional proteins) supported these findings. In total, 20 wound-response proteins and one unknown protein were identified as having important roles in the signaling response to wounding, response to stress, activation of plant defense systems, and plant regeneration. The detected biological processes include brassinosteroid stimulus, polyamine catabolism, hypersensitive response, response to cadmium ions, response to oxidative stress, and malate metabolism, suggesting that the wounded trees must have undergone major plant cell damage. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis indicated that several wound-response proteins were involved in agarwood formation. Our proteomics data thus provide useful information for understanding the wound response mechanisms that trigger agarwood formation.