טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentDor Chen
SubjectIdentification and Characterization of Senescence
Associated Genes in Arabidopsis Leaves
DepartmentDepartment of Biotechnology
Supervisor Professor Emeritus Shimon Gepstein


Abstract

Leaf senescence, the final stage of leaf development preceding death, is characterized by dramatic catabolic changes resulting in extensive breakdown of major macromolecules, followed by cell dysfunction and disintegration. Plant senescence is a form of programmed cell death, and is believed to involve preferential expression of specific set of senescence-associated genes (SAGs).

A potent and a useful strategy to better understanding the multiple biochemical pathway and cellular events of the senescence process is to analyze the preferential gene expression during this stage. It is speculated that targeted manipulation of key senescence-associated genes might change the senescence pattern: delay leaf senescence and might have an impact on crop yield. This manipulation is also expected to extend shelf life of crops.

In this research, we have used the library of cDNA clones isolated by the suppression subtractive hybridization (SSH) representing genes preferentially expressed during leaf senescence.

About 70% of the SSH clones were confirmed by Northern analysis to be differentially expressed during senescence. Each of the individual clones was sequenced and homology analysis was performed. Based on their putative function, the SAGs were classified into the following five classes: protein degradation, detoxification and defense mechanisms, nutrient remobilization, genes associated with non senescing processes and genes encoding hypothetical proteins.

Kinetic studies showed the following three temporal patterns: genes with basal expression during pre-senescence stages, genes with enhanced expression in early senescence and genes displaying transient expression. Darkness promoted gene expression whereas ethylene accelerated expression of most studied genes. Light and cytokinins inhibited the expression of all studied genes.

In conclusion, the SAGs we have examined show a variety of expression patterns in response to factors other than age-related senescence. These expression patterns can provide clues to both the roles of the individual SAGs and the relationship between senescence and the various senescence regulatory pathways.