טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentInbal Yariv
SubjectIsolation, Identification and Characterization of
Senescence-Specific Genes
DepartmentDepartment of Biology
Supervisor Professor Emeritus Gepstein Shimon


Abstract

Leaf senescence is the final stage of leaf development preceding death. Plant senescence is a form of programmed cell death, and is believed to involve preferential expression of a specific set of “senescence-associated genes” (SAGs). To identify non-abundant genes, we used suppression subtractive hybridization (SSH). The differential expression of the identified SAGs was confirmed by Northern blot analysis. Twenty-six SAGs have been isolated. Each of the individual clones was sequenced and homology analysis was performed by the BLAST program. Based on the deduced function, several categories of SAGs have been identified. SAGs are associated with transcription regulation, macromolecular degradation and recycling, detoxification, Stress, pathogenicity and synthesis of secondary metabolites.

In Arabidopsis, WRKY6 is a plant-specific transcriptional regulator controlling several types of plant stress responses. Together with the group of R. Hehll, we have identified a potential module made up of two elements which might be responsible for the regulation of the WRKY6-target genes by WRKY6. The relevance of this module was tested by a gene expression screening of our SAGs library.

We have succeeded in manipulating specific SAGs, resulting in 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, as well as premature death of the whole plant. Anti-sense expression of the Arabidopsis LLS1 gene did lead to any phenotypic changes as compared to wild type. LLS1 is hypothesized to function by breaking down a phenolic mediator of cell death in plants, however, the precise function of LLS1 remains to discover.