Porri, Aimone (2013). Tissue specific action of Gibberellin in Arabidopsis flowering and development. PhD thesis, Universität zu Köln.

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This work focuses on understanding the roles of the plant hormone gibberellin (GA) in controlling the initiation of flowering in Arabidopsis thaliana. GA is essential to promote the transition to flowering under non inductive short-­‐day (SD) photoperiods by activating transcription of the floral integrator SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) and of the meristem identity gene LEAFY (LFY). However, mutations in GA receptors also prevent flowering under inductive long days (LDs), suggesting that this hormone also has crucial functions in the initiation of flowering under these conditions. Here by overexpressing the GA catabolic enzyme GIBBERELLIN 2 OXIDASE 7 (GA2ox7) in specific plant organs, we show that GAs play important regulatory roles in the leaves and shoot apical meristem (SAM) to promote flowering under LDs. Our results suggest that GAs are required in the leaf to increase levels of FT mRNA, which encodes a protein that is part of the systemic florigen signal of Arabidopsis. At the SAM GAs promote expression of SQUAMOSA PROMOTER BINDING PROMOTER LIKE (SPL) genes downstream of the floral integrator SOC1. In addition, we characterised a novel function of the MADS box transcription factor SHORT VEGETATIVE PHASE (SVP) and demonstrated its link to the GA biosynthetic pathway at the SAM. Mutation of SVP results in a significant accumulation of active GA4 through the upregulation of GIBBERELLIN 20-­‐OXIDASE 2 (GA20ox2), which encodes an enzyme involved in GA biosynthesis. Conversely overexpression of SVP from the 35S promoter causes phenotypes characteristic of GA deficiency plants. We demonstrate that the SVP/GA20ox2 module is controlled by photoperiod through FT, TSF and SOC1 at the SAM. Wild-­‐type plants shifted from SDs to LDs showed downregulation of SVP in the centre of the SAM and increased levels of GA20ox2 transcripts in the rib meristem region. These expression patterns are significantly compromised in plants lacking FT, TSF or SOC1 functions. We propose that in response to LDs, FT, TSF and SOC1 act to repress expression of SVP leading to upregulation of GA20ox2. The activation of GA20ox2 expression causes increased GA content, which promotes flowering by activating transcription of SPL genes. Finally, we identified a link between a core subunit of chromatin remodelling complexes (CRCs) SWI3C and the GA signalling and biosynthesis pathways. The swi3c mutant displayed several developmental impairments, which resembled those of GA deficient plants. In agreement with the phenotypic characterization, swi3c mutants showed lower levels of active GAs and reduced mRNA abundance of the GA receptor GIDa, suggesting that SWI3C is required to control development by modulating GA biosynthesis and perception. Moreover we demonstrate that SWI3C binds in vivo to some of the DELLA repressors (RGA, RGL1, RGL2, RGL3) and SPY O-­‐GlcNAc transferase, two components of the GA signalling pathway. Our results indicate that CRCs control plant development at least in part by promoting GA biosynthesis, and by regulating expression of some GA responsive genes. Overall this work increases our understanding of the regulation of GA biosynthesis and signalling, as well as demonstrating new functions for these processes in the control of the floral transition.

Item Type: Thesis (PhD thesis)
CreatorsEmailORCIDORCID Put Code
Porri, Aimoneporri@mpipz.mpg.deUNSPECIFIEDUNSPECIFIED
URN: urn:nbn:de:hbz:38-53313
Date: 16 October 2013
Language: English
Faculty: Faculty of Mathematics and Natural Sciences
Divisions: Faculty of Mathematics and Natural Sciences > Department of Biology > Institute for Genetics
Subjects: Natural sciences and mathematics
Life sciences
Uncontrolled Keywords:
Date of oral exam: 14 October 2013
NameAcademic Title
Coupland, GeorgeProf. Dr.
Refereed: Yes
URI: http://kups.ub.uni-koeln.de/id/eprint/5331


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