טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentEfrat Valensi
SubjectInvolvement of the Transcription Factor WRKY6 in the
Regulation of Arabidopsis Leaf Senescence
DepartmentDepartment of Biology
Supervisor Professor Emeritus Gepstein Shimon


Abstract

Plant senescence is the final developmental stage which involves a cascade of morphological, physiological and biochemical changes occurring at all the levels. Although total protein and RNA levels decrease in senescent leaves, expression of specific genes is turned on during senescence. It is assumed that these specific genes play an important role in senescence. These genes have been named Senescence Associated Genes (SAGS). 

Transcription factors play an important role in the regulation of many developmental processes including senescence. The transcription factor WRKY6 is particularly relevant to the senescence research since our studies revealed delayed senescence phenotype in WRKY6 knock-out plants.

The hypothesis underlying this research is that the WRKY6 transcription factor activates genes associated with senescence by binding to promoters that contain at least two nearby repetitions of W box elements (containing the sequence TTGAC).

Two independent methods were used for studying the association of WRKY6 with W-box elements in promoters of SAGS: Real-Time RT PCR and One Hybrid. Surprisingly, the results of the Real-Time RT PCR analysis showed no decrease whatsoever in mRNA levels in the knock-out plant. Rather, three out of the four tested genes showed an increase in the knock-out plant, as compared with the wild-type plant (PHGPX, Vsp2, At5g20900 and CAD).  By contrast, the results of the One-Hybrid analysis partially support the hypothesis.  In agreement with the working hypothesis, WRKY6 binds to and activates two promoters with a duplicated W-box (SIRK and Small G protein) and also, WRKY6 suppresses the two negative control promoters (WRKY6 promoter and metallothionein). It is not possible to determine whether WRKY6 is not bound or bound indirectly to four additional tested promoters (CAD, PHGPX, Vsp2 and Putative calcium binding protein). Cross checking three of these four promoters (CAD, PHGPX and Vsp2) with Real-Time RT PCR indicated that the WRKY6 does not activate these genes.  Thus, it appears that the hypothesis has been verified only in part, and may be incomplete.