|M.Sc Student||Orna Nesher|
|Subject||Identification of Senescence-Associated Genes Isolated|
by a Subtraction Library
|Department||Department of Biology||Supervisor||Professor Emeritus Gepstein Shimon|
Senescence is the last stage of leaf development. During senescence, cells undergo a major transition from anabolic to a catabolic pattern that results in cell dysfunction, structural disintegration and, eventually, cell death. Biochemical and molecular studies have provided evidence that leaf senescence is an active and genetically programmed process, responding to external and internal signals by either accelerating or delaying its time course.
Genes that are up-regulated during senescence are defined as senescence-associated genes (SAGs).
Using the SSH technique we have isolated 20 novel SAGs, in Arabidopsis leaf, whose steady-state mRNA levels increased during age-mediated senescence. The identified SAGs were classified into 4 groups, based on their function: genes involved in proteins metabolism: cysteine protease, cationic amino acid transporter, ubiquitin conjugating enzyme (E2); genes involved in biosynthesis of natural products and cofactors: squalene epoxidase, copper amine oxidase like protein, lipoic acid synthase, limonene cyclase like protein; genes involved in signal transduction: myo-inositol 1 phosphate synthase, calmodulin like protein, cyclic-nucleotide and calmodulin regulated ion channel; and genes encoding hypothetical proteins.
Four expression patterns during were demonstrated various developmental and senescence stages of Arabidopsis leaf, and a variety of expression patterns in response to factors other than age-related senescence (darkness and hormones).
To further investigate the role of specific SAG in leaf senescence, we have produced an over expressing transgenic plant of the SAG-602-(Lip1) encoding lipoic acid synthase, and SAG-608-(Inps1) encoding myo-inositol 1-phosphat synthase. The Lipl transgenic plant didn't survive and the Inps1 didn't exhibit any morphologically distinguishable phenotype.