Purdy, SJ; (2007) Genetic analysis of the metabolic regulation of senescence in Arabidopsis thaliana. Doctoral thesis , UCL (University College London).

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Abstract

Leaf senescence is a sensitive and dynamic process that is both genetically and environmentally controlled. Environmentally, factors such as daylength and nitrogen availability are understood to affect the timing of senescence, but the underlying genetic factors that initiate the processes that result in leaf death remain elusive. Sugars and nitrogen can act at the molecular level as signalling molecules which result in altered gene expression. Sugars were found to accumulate in senescing leaves suggesting that leaf senescence is not caused by sugar starvation. Nitrogen decreases in senescing leaves as it is exported to young leaves and the developing fruits. This study presents evidence that the alteration in the ratio between these two essential nutrients may act as the instigating signal for leaf senescence. On medium containing 2% glucose in combination with low nitrogen supply senescence was accelerated. The expression of a number of genes, functional during developmental senescence was altered by the addition of glucose. The expression of SAGI2. a senescence specific gene, confirmed that accelerated senescence was not caused by stress and also that glucose-induced senescence was representative of developmental senescence. Quantitative trait loci analysis was carried out on the Bay-0 x Shahdara population in response to treatment with low nitrogen plus 2 o glucose. The decline in maximum photosynthetic efficiency (F /Fm) was monitored by chlorophyll fluorescence imaging to determine the extent of senescence of the whole rosette. Using Fx/Fm as quantitative trait, two new loci, on Chromosomes II and IV. were mapped that regulate glucose-induced senescence. The use of near isogenic lines confirmed the locus on Chromosome IV. The study of flowering uncovered a strong link between flowering time and senescence in the RIL population. In one RIL. 310. flowering was severely retarded and glucose did not induce senescence. This was confirmed by the absence of SAG 12 expression in glucose-treated plants. Of particular interest was that FRIGIDA. a gene involved in vernalization- dependent flowering, mapped to the QTL on chromosome IV. This gene was subsequently nominated as a candidate gene.

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