Quantitative proteomic analysis of auxin signaling during seedling development

Auxin induces rapid gene expression changes throughout plant development. How these transcriptional responses relate to changes in protein abundance is not well characterized. We have identified auxin regulated proteins in whole seedlings, roots and hypocotyls and at three different time points (30 min, 120 min and 3 hours) using an iTRAQ (isobaric tags for relative and absolute quantification) based quantitative proteomics approach. These profiling experiments detected 4,701 proteins from seedling tissue, 6,740 proteins from root tissue and 3,925 proteins from hypocotyl tissue. Comparisons between the differentially expressed proteins data sets showed little overlap, suggesting that auxin proteomes exhibit both temporal and spatial specificity. Numerous proteins showed significant changes in abundance following auxin treatment independent of changes in cognate transcript abundance. This includes several well characterized proteins with various roles in auxin pathways, suggesting that complex gene regulation mechanisms follow auxin signaling events. Specifically, regulation of translation may play a role as inferred from MapMan categorization analyses and protein interaction networks comprised of auxin regulated proteins. Additionally, functional categorization of auxin regulated proteins indicates rapid and complex metabolic changes occur in both roots and hypocotyls in response to auxin which are not apparent from transcriptome analyses. Altogether these data describe novel auxin-regulated proteomes and are an excellent resource for identifying new downstream signaling components related to auxin-mediated plant growth and development.