טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentYael Hacham
SubjectMethionine Metabolism in Plants:The N-Terminal Region of
Cystathionine Gamma Synthase from Arabidopsis
Plays an Important Regulatory Role in
Methionine Metabolism
DepartmentDepartment of Biology
Supervisors Full Professor Schuster Gadi
Professor Rachel Amir


Abstract

The sulfur-containing amino acid, methionine, is an important essential amino acid in animal nutrition but exists at extremely low levels in many crop plants. Methionine is also the precursor of several key materials in plants such as ethylene, polyamines and Biotin. The control of methionine biosynthesis is being clarified gradually only now. Cystathionine g-synthase (CGS), the key enzyme in the biosynthesis pathway of methionine, contains an extended N-terminal region in plants (in addition to the plastid transit peptide) in comparison to bacterial enzymes. Since this region is not essential for catalytic activity, it may be responsible for the modulation of CGS activity and hence methionine metabolism. Indeed, tobacco plants over-expressing a truncated Arabidopsis enzyme that lacks the N-terminal region displayed a severely abnormal phenotype and emitted high levels of methionine catabolic products, including ethylene. These results suggest that the CGS N-terminal is important for proper methionine metabolism, preventing the over-production of harmful catabolites such as ethylene. However, over-expression of the deleted version of CGS, which lacks 30 amino acids in this N-terminal region, causes a significant over-accumulation of the soluble methionine, while the phenotype of the plants and their ethylene production were similar to the wild-type plants. The results suggested that the N-terminal region has important motives for CGS modulation and methionine metabolism, which may operate via unknown factors binding to this region. Understating these motives will add to our basic knowledge about the molecular mechanism regulating methionine metabolism in plants and it also may lead to producing crop plants having increased methionine levels.