M.Sc Thesis

M.Sc StudentMiller Tamar
SubjectGenes Involved in Regulation of Root Elongation under Water
Deficit in Arabidopsis
DepartmentDepartment of Civil and Environmental Engineering
Supervisors PROFESSOR EMERITUS Peter Neumann
Full Thesis textFull thesis text - English Version


Abiotic stresses such as water, salinity or heat stress can cause major inhibitory effects on plant growth. The root is the plant organ responsible for absorbing essential mineral nutrients and water from the soil and transfering them to the whole plant. Under drying conditions at the soil surface, increased root ability to continue to mine deeper soil layers for nutrients and water could have beneficial effects on plant survival, growth and eventual crop yields. Research into factors controlling root growth is scientifically important and has potential practical applications in agriculture.  

In previous research, genes involved in root elongation were examined along primary root tips of maize (Zea mays) seedlings using suppression subtractive hybridization (SSH). 42 non-redundant cDNA clones representing root growth-related-genes (RGG) that were preferentially expressed in the elongation zone were found. Using bioinformatic and molecular biology techniques four of the maize genes, which appeared to have regulatory roles, were selected for further investigation in model organisms - yeast and Arabidopsis. Of these genes, two genes have shown encouraging results.

The first gene was RGG7B. This gene showed strong homology to AtSK12 in Arabidopsis. AtSK12 is a member of the shaggy-related-protein kinase family. In order to examine the actual metabolic function in-vivo of AtSK12, yeast complementation analysis was performed. A yeast strain defective in RIM11 (the yeast homolog of AtSK12) does not sporulate. When AtSK12 from Arabidopsis was transformed into the RIM11-defective yeast strain the capacity for sporulation was partly restored. This directly confirmed AtSK12 function as a regulatory gene.

The second gene was RGG385 that showed homology to hsf2 from Arabidopsis. Hsf2 belongs to the heat-shock-factor family of regulatory proteins. Two homozygous lines of Arabidopsis with TDNA insertion knockout for this gene were identified and compared to wild type plants under control conditions and under abiotic stresses. Knockout plant were more sensitive to drought stress than WT and the roots of the knockout plants elongated less than WT roots under control, osmotic and heat stress conditions. Under salinity stress roots of only one of the lines of knockout plants elongated less than WT roots. Overall, these findings suggest that hsf2 gene is required for optimal plant root elongation under control and stress conditions. This gene is therefore a good candidate for further investigations involving over-expression, in order to produce plants with better root growth capacity and hence, better chances to survive and flourish under abiotic stresses.