2018-06-012024-05-13https://scholars.lib.ntu.edu.tw/handle/123456789/655160Abstract: Phytohormone ethylene plays important role in regulating developmental processes in plants. Many ethylene response factors (ERFs) are known to be involved in stress responses in plants. Ethylene biosynthesis enzyme 1-aminocyclopropane-1-carboxylate (ACC) synthase (ACS) is the key enzyme and classified into three types. Our precious study found that an Arabidopsis type III ACS, AtACS7, is involved in root gravitropism in a calcium-dependent manner in Arabidopsis. Mutation of ACS7 led to less sensitivity to inhibition of root gravitropism by calcium channel blocker LiCl. In addition, AtACS7 interacts with 14-3-3 protein (a phosphoprotein interactor), and can be phosphorylated by Arabidopsis calcium-dependent protein kinase16 (CDPK16) in vitro. Moreover, other group reported that AtACS7 is involved in abscisic acid (ABA) sensitivity and salt stress tolerance. acs7 mutant exhibited enhanced salt tolerance and hypersensitivity to ABA in seed germination. However, the molecular mechanism is little known. We hypothesize that 14-3-3 interaction with AtACS7 and affects salt stress response and ABA signaling in a calcium dependent manner. To elucidate the molecular mechanism of AtACS7 participating in salt stress tolerance and ABA signaling, we propose the following experiments. We will perform a microarray study on salt stress and ABA-treated acs7 mutant line and identify any AtACS7-regulated gene. Our preliminary results identified three phosphorylation sites of AtACS7. We will confirm which site is the 14-3-3 binding site. Three phosphorylation sites of AtACS7 will be point-mutated and tested for protein stability and enzyme activity to determine the effects of 14-3-3 binding. The AtACS7 phospho-mimicking overexpression lines as well as and acs7 mutant line complemented with phosphorylation sites mutated to alanine will be generated and subjected to phenotyping by salt stress and ABA treatment. In addition, ethylene and ABA amount, and ABA-related gene expression in these lines will be measured using GC/LC-MS and quantitative PCR. Moreover, same approaches will also be introduced to study type III ACSs in rice (Oryza sativa). The proposed study will provide in-depth knowledge of mechanism of how ethylene regulates salt stress response by cross-talking to ABA signaling in plants. Eventually we hope that we can apply these to engineer crops (i.e. rice) to improve salt stress tolerance.CDPKABA14-3-3ethylenesaltLiCl.