![]() This parameter is sensitive to the local environment of fluorescent probes and therefore can be exploited to illuminate cellular processes in live cells and tissues. However, the fluorescence lifetime τ is an additional parameter of fluorescence microscopy. Most imaging approaches, like confocal microscopy, only rely on fluorescence intensities as read-outs. One of the main microscopic methods applied throughout this thesis was fluorescence lifetime imaging microscopy (FLIM). For this purpose different fluorescence imaging techniques were applied, which allowed investigating the spatiotemporal localization and interaction dynamics of BRI1 and SERK3 in their natural environment. The aim of this thesis was to describe BRI1-mediated signal transduction and the respective role of SERK3, the main coreceptor of BR signaling (Albrecht et al., 2008), at (sub)cellular level in Arabidopsis roots. Even though the molecular determinants of BR signaling have been revealed, full mechanistic detail is still missing. Based on these findings a model for BRI1-mediated signal transduction was established, which often serves as a paradigm for plant PM receptor signaling. In the first Chapter of this thesis, the BR signaling pathway was introduced in further detail and it was highlighted how genetic and biochemical approaches attributed to the identification of cellular components that link signal perception of BRs at the PM to BR dependent transcriptional regulation in the nucleus. Besides their role as coreceptors of BRI1, the SERKs have also been implicated in various other signaling processes like somatic embryogenesis, male fertility, cell death regulation and plant immunity (Chinchilla et al., 2009). Three members of this protein family are involved in BR signaling: SERK1, SERK3 (also known as BAK1 for BRI1-associated kinase 1), and SERK4 (also known as BKK1 for BAK1-like kinase 1). These coreceptors belong to the family of Somatic embryogenesis receptor-like kinases (SERKs) and have a related structural architecture to BRI1, but with a smaller extracellular domain. ![]() During the last decade it has been shown that BRI1 indeed perceives BRs at the PM (Kinoshita et al., 2005), however, initiation of BR signal transduction requires interaction of BRI1 with other, non-ligand binding receptors (Nam and Li, 2002 Wang et al., 2008 Gou et al., 2012). This class of phytohormones regulates several aspects of plant growth and development (Kutschera and Wang, 2012). Since the discovery in 1997 (Li and Chory, 1997) its mode of action has been studied extensively and has resulted in the elucidation of a complete set of molecular components constituting the brassinoteroid (BR) signal transduction pathway (Clouse, 2011).īRs, the ligands of BRI1, are a group of polyhydroxy lactones that are structurally similar to animal steroid hormones (Grove et al., 1979). One of the best-described plant LRR-RLKs is the Brassinosteroid insensitive 1 (BRI1) receptor. They comprise an extracellular LRR domain for ligand binding, a transmembrane domain, which anchors them within the plasma membrane (PM) of their host cells, and an intracellular kinase domain for transducing the event of ligand binding into the cell interior. In plants, many of these receptors belong to the class of leucine-rich repeat receptor-like kinases (LRR-RLKs) (Shiu and Bleecker, 2001). Collectively, these processes of signal perception, signal transmission and cell adaptation represent so-called signal transduction pathways.įor the perception of signals such as hormones or pathogens cells are equipped with receptors that are often located at the cell surface. These receptors perceive specific signals, which, in turn, initiate a sequence of molecular events within the cells that convert signal perception into an adequate physiological response. In the course of evolution, cells have developed mechanisms to detect and adapt to environmental and endogenous cues by the use of a wide array of receptors (Afzal et al., 2008). Living matter is continuously challenged by the dynamics of its environment and intrinsic fluctuations. ![]()
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