|M.Sc Student||Sabehi Gazalah|
|Subject||Functional Genomics of the Leaf Senescence Process: From|
the Isolated Gene to the Transgenic Plant
|Department||Department of Biology||Supervisor||Professor Emeritus Shimon Gepstein|
The leaf, a specialized photosynthetic plant organ, undergoes a gradual functional deterioration during senescence, the last developmental stage that precedes its death.
Since leaf senescence is a genetically programmed process, it is hypothesized that a set of senescence-associated genes (SAGs) are (specifically) unregulated during the senescence stages.
In this research, we have isolated 19 SAGs by suppression subtractive hybridization (SSH) technique. Based on their function, the SAGs were classified into 5 classes: genes related to cell wall, genes involved in protein metabolism, pathogen and stress-related genes ,genes encoding transcription factors or involved in signal transduction and genes encoding hypothetical proteins. The various SAGs displayed different expression profiles suggesting that their transcription is regulated by variety of complex mechanisms.
To investigate the role of specific SAG in leaf senescence, we have manipulated some of the SAGs. Transgenic plants, which overexpressed SAG9, encoding hypothetical protein and a knockout mutant of the AALP (Arabidopsis aleurain-like protein) gene were compared with the wild-type plants but did not exhibit any morphologically distinguishable phenotype. Since, leaf senescence is a complex process and is probably regulated by several regulatory pathways, gene manipulation of one SAG would not necessarily alter the senescence syndrome.
One of the transgenic plants that were manipulated caused dramatic changes in the senescence pattern. Over-expression of the Arabidopsis Lls1 (lethal leaf spot 1 homolog) gene caused non-restricted cell death during late stages of leaf development followed by a premature death of the whole plant. This gene may represent a common link between the hypersensitive response (HR) to pathogenic attack and the natural leaf senescence process.