Quantitative phosphoproteomic analysis of ethylene signal transduction pathway in arabidopsis and its consitutive triple response mutant ctr1-1

Ethylene, a simple gaseous hormone, plays multiple roles in plant growth,development, and stress tolerance. Over the past decade, intensive studies were done on signal transduction pathway via genetic analysis. The functional genomic approach has identified a number of critical components in ethylene signaling. One of the key components in ethylene signaling cascades is CONSTITUTIVE TRIPLE RESPONSE1 CTR1, a Raf-like protein kinase negatively regulating the signal transduction. As one of the MAPK directly interacts with ethylene receptor, the downstream signals to transcriptional level remain unknown. Phosphorylation is one of the post-translational modifications found to be a key regulator for transducing the signal. The gap in our understanding of the ethylene signaling pathway is the way that the phosphorylation events of this component regulate the signal transduction. We have adopted a mass spectrometry-based quantitative phosphoproteomics approach to investigate the differentially phosphorylated sites and measure changes in phosphorylation level in long-term ethylene-treated wild type Arabidopsis compared with the CONSTITUTIVE TRIPLE RESPONSE1 ctr1-1 mutant. The SILIA method (15^N Stable Isotope Labeling In Arabidopsis) was used in this approach. Our data identified total 70 CTR1 relative phosphopeptides repetitively with one or more differentially phosphorylated sites. 17 out of 178 phosphopeptides quantified showed a statistically significant difference between Col-0 and ctr1-1. 6 peptides were up-regulated by CTR1 and 2 were down-regulated by CTR1. Together with in vivo testing, a sub-network of the ethylene signaling network can be reconstructed. Our data provides new sources and a more realistic image to gain novel insight into ethylene signaling in plants