Universität zu Köln

Willee, Eva (2018). Analysis of light-dependent leaf development in Arabidopsis and cotyledon development in Flaveria species. PhD thesis, Universität zu Köln.

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Abstract

Light not only provides the electromagnetic radiation plants need to perform photosynthesis, it is also an important environmental factor for plant development. Internal leaf architecture is one of the most essential features of plant development. Leaf architecture adaptations such as cell elongation and leaf vein density increase towards light intensities and enable the plant to optimize the photosynthesis rates and water use efficiency. This thesis comprises two different approaches to analyse light-dependent regulators of leaf development. The first one involves the analysis of light-dependent C4 photosynthesis-specific Kranz anatomy in Flaveria species. The second approach utilizes the genetic variation of Arabidopsis accessions and next generation sequencing. Kranz anatomy is a very specific leaf architecture composed of bundle sheath cells (BSC) that surround the veins and furthermore features reduced vein spacing. In this thesis, I investigated the light-dependent formation of the Kranz anatomy by analysing the BSC area increase in Flaveria species. In all species analysed comprising C3, C3-C4 and C4 species, the increase of BSC area was light-dependent. Since several genes of the C4 photosynthetic pathway are expressed in a light-dependent matter, another research question of this experiment was, whether the promoters of GLDPA and PPCA deriving from Flaveria trinervia show light-dependent activation. Here, light-dependent expression of two reporter genes was not verified in dark-and light-grown cotyledons of Flaveria bidentis and Arabidopsis. In a second approach in order to understand leaf development, quantitative trait loci (QTL) analysis was performed to identify regulators of estimated leaf thickness and leaf vein density in Arabidopsis. A QTL on chromosome 4 for leaf vein density was identified using the Arabidopsis multiparent recombinant inbred lines (AMPRIL) and SNP-based polymorphism analysis in the parental accessions of the RILs lead to the identification of AXR6 as the putative QTL for leaf vein density. The last part of this thesis comprises the transcriptome analysis of high-light- and low-lightgrown Arabidopsis leaves. Using 3 leaf-developmental stages this experiment gives insight into the transcriptome of developing high-light stressed Arabidopsis leaves. In summary, I confirmed light-dependent BSC area increase in different Flaveria species. In the used model systems, the expression of GLDPA- and PPCA-reporter constructs was found to be light-independent. QTL analysis using AMPRIL lead to the identification of AXR6 as putative QTL for leaf vein density. Transcriptome analysis of high-light- and low-light-grown Arabidopsis leaves gave first insights into differentially expressed genes in developing leaves and requires further investigations