Browsing by Subject "white"

Tiivistelmä – Referat – Abstract Plant lives and grows in variable environment and climate conditions. Everyday plants can be confronted with a variety of abiotic (temperature, light, salt, water availability) and biotic stress (pathogens, insects etc). These abiotic and biotic stress can halt plant growth and influence crop productivity. Plant has evolved signaling mechanism and different responses to adapt or respond with these unfavorable environmental conditions. Our group’s previous research identified a new mutant in the model plant Arabidopsis thaliana with a striking phenotype – when the plants ages it progressively becomes yellow and eventually the entire plant is white. The mutant was named “white” after its striking appearance. The phenotype is associated with increased accumulation of mRNA transcript for stress and senescence regulated genes. Mapping of the mutation identified a 4 bp deletion in a gene EGY1 that encodes a metalloprotease located in the chloroplast. To identify molecular mechanisms that regulate this unusual type of premature senescence, a suppressor mutants screen was performed in the white mutant, and three suppressors that restore normal appearance to the plant was identified. Mapping of one of these suppressors, identified a mutation in STAY GREEN1 (SGR1) as a likely candidate. SGR1 encodes the protein that catalyze the first step in chlorophyll breakdown, removal of Mg2+ from chlorophyll. The overall aim of my master thesis was to understand the molecular mechanisms behind the development of the age and chlorophyll related phenotypes in the white mutant and its two suppressors S1 and S2. Furthermore, with gene expression analysis, plant stress and senescence responses were studied in white, S1 and S2. By complementation method I proved that mutations in SGR1 gene caused the development of suppressor mutant phenotype and restoration of wild type allele of SGR1 gene restore white phenotype in suppressor mutant. Measurements of chlorophyll concentration provided further evidence that the mutation in SGR1 stabilizes the suppressor mutant phenotype, stops chlorophyll breakdown and keep the leaves green. Gene expression study using qPCR with marker genes provided insight of molecular changes within these phenotypes.