Universität zu Köln

van Driel, Annabel D. ORCID: 0000-0002-1629-5961 (2021). Characterisation of Transcription Factor SPL15, an Integrator of Multiple Flowering Time Pathways. PhD thesis, Universität zu Köln.

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Abstract

The transition from vegetative to reproductive development in plants is tightly controlled to ensure their reproductive success. Plants integrate many different environmental signals to flower at the appropriate time, and complex regulatory networks underlie this decision. In Arabidopsis thaliana, the model organism for plant molecular research, the timing of floral transition is influenced by environmental cues, which include temperature and day length, and by internal factors, including the age of the plant and the levels of the phytohormone gibberellin. During the transition, Arabidopsis switches from producing leaves to producing flowers, a process that includes morphological and identity changes in the shoot apical meristem (SAM). In favourable environmental conditions, such as floral inductive long-days, Arabidopsis accelerates the floral transition and quickly bolts and flowers. In the absence of floral inductive signals, these plants still undergo the floral transition, but do so later after producing many more leaves. The transcription factor SQUAMOSA PROMOTER BINDING PROTEIN LIKE 15 (SPL15) promotes flowering in non-inductive conditions. SPL15 integrates signals from multiple floral induction pathways at the shoot apical meristem and is proposed to directly activate transcription of two other genes with a prominent function in flowering: FRUITFULL (FUL), which encodes a MADS box transcription factor, and MICRORNA172b (MIR172B), which encodes a short non-coding RNA. However, the precise role of SPL15 in floral induction remains unknown. To gain understanding of the importance of SPL15 targets and other downstream components, I genetically assessed their contribution to floral induction. I found that FUL and MIR172B were important for SPL15 function during floral induction. However, in their absence, increased expression of SPL15 still induced early bolting of the inflorescence, but could not induce floral development. These analyses suggested that SPL15 regulates more target genes than FUL and MIR172B during the floral transition. Subsequently, I identified the binding sites of SPL15 in the FUL promoter, and studied the effect of mutating them. This revealed that SPL15 is not the only SPL protein that recognises these sites to regulate floral transition. I therefore propose that during vegetative growth, other SPLs bind there to repress the expression of FUL. Lastly, I set out to identify additional putative target genes of SPL15 by two complementary transcriptome analyses. The resulting high confidence list of putative target genes of SPL15 showed that SPL15 likely regulates several other genes with described functions in floral induction. In addition, SPL15 regulates a set of genes with functions in cell proliferation, which might be relevant for the morphological changes occurring in the SAM during the floral transition. Altogether this thesis has contributed to a better understanding of how SPL15 regulates different stages of the floral transition in A. thaliana under non-inductive conditions.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code van Driel, Annabel D. annabel.vandriel@wur.nl orcid.org/0000-0002-1629-5961 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-530801
Date:	28 August 2021
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 Agriculture
Uncontrolled Keywords:	Keywords Language Arabidopsis English Flowering UNSPECIFIED FRUITFULL UNSPECIFIED SPL15 UNSPECIFIED SQUAMOSA PROMOTER BINDING PROTEIN UNSPECIFIED MICRORNA UNSPECIFIED
Date of oral exam:	28 August 2020
Referee:	Name Academic Title Coupland, George Prof. Dr Hoecker, Ute Prof. Dr
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/53080