Ethylene Lab Report

The gaseous hormone ethylene has been shown to influence a diverse array of plant growth and developmental processes, thus it is critical for plants to optimize the ethylene production at developmental transitions as well as during stress response. Ethylene is derived from the amino acid methionine, which in the first step is converted to S-adenosyl-methionine (AdoMet) by AdoMet synthetase3,4. The 1-Aminocyclopropane-1-Carboxylic acid Synthase (ACS) catalyzes the conversion of AdoMet to 1-aminocyclopropane-1-carboxylic acid (ACC)5, which is the rate-limiting step in ethylene biosynthesis. ACC is then converted to ethylene by ACC oxidase (ACO), a member of the oxygenase/oxidase superfamily of enzymes6.The ACS plays a central role to regulate ethylene production through changes in ACS gene expression levels and the stability/activity of the enzyme. ACS proteins can be divided into 3 groups (type-1, 2 & 3) based on their C-terminal domain and the presence of phosphorylation sites. Type-1 and -2 ACS isoforms contain phosphorylation sites for kinases, but type-3 lacks of the phosphorylation sites.
Pathogen-activated Mitogen Activated Protein Kinase 6 phosphorylates type-1 ACS (ACS2 & ACS6), which lead to increased accumulation of these ACS isoforms and, hence, increased ethylene production 20. A Casein Kinase 1 phosphorylates type-2 ACS5, resulting in the degradation of ACS5 protein 11. Our previous studies also suggested that phosphorylation is likely involved in ACS stabilization. We demonstrated that 14-3-3 is a novel regulatory element in ethylene biosynthesis21. 14-3-3 proteins are evolutionally well-conserved proteins that interact specifically with phosphorylated proteins to regulate their localization, stability, or activity21,23. 14-3-3 proteins interact with all three types of ACS and, surprisingly, with ETO1/EOL as well, and as results, control the protein turnover of both ACS and