Universität zu Köln

Tergemina, Emmanuel (2017). Natural variation at FLOWERING LOCUS T in Arabidopsis thaliana. PhD thesis, Universität zu Köln.

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Abstract

Flowering time is a complex trait that is crucial for fitness and regulated by seasonal changes and internal cues. In the annual plant Arabidopsis thaliana (Arabidopsis), two lifestyles have been described; winter accessions flower in response to long exposure to cold temperatures (vernalization) and single season accessions flower in a short period chiefly in response to long-days (LDs). The control of these two lifestyles converges at the level of transcriptional regulation of floral integrator genes, including the florigen encoding gene FLOWERING LOCUS T (FT). Indeed, FT expression, which is repressed prior vernalization in winter accessions, strongly accelerates flowering mainly in response to LDs but also to elevated temperatures. The photoperiodic induction of FT expression requires a 5,7 kb region upstream of the start codon of FT. This area contains a proximal promoter and a distal enhancer phylogenetically conserved among the Brassicaceae. However, the distal enhancer is not required in the regulation of FT expression in the siliques, which has been proposed to influence related traits like floral reversion and seed dormancy. While most of the flowering time quantitative trait loci (QTL) identified in Arabidopsis have been associated with variation at coding regions, QTLs closely linked to FT were exclusively mapped to non-coding regions. To test whether FT could be a target of selection to modulate flowering time, we dissected paired-end short read sequences from the 1001 genomes project for single nucleotide polymorphism and structural variation at the photoperiod control regions of FT. We identified rare FT haplotypes defined by natural variation in cis-regulatory elements of FT previously characterized in our group. In the rosette leaves, prior the floral transition, allele-specific expression (ASE) of FT in F1 hybrids revealed FT haplotypes less responsive to both LDs and ambient temperatures. Interestingly, the ASE of FT in developing siliques of F1 hybrids showed a symmetric pattern, indicating that the causal natural variation does not affect the expression of FT in the siliques. ASE in F1 hybrids and complementation experiments also revealed an FT haplotype, present in slow vernalization behavior accessions, relatively insensitive to inductive conditions in the rosette leaves. This last observation led us to investigate the effect of the florigen after extended vernalization. Surprisingly, the total number of leaves of ft-10 tsf-1 double mutants is comparable to wild-type plants after prolonged periods of cold temperature. These findings redefine the impact of FT on flowering time after extended periods of cold temperature. I propose that FT haplotypes less responsive to inductive conditions in the rosette leaves could accumulate in Arabidopsis populations with slow vernalization behaviors due to a relaxed purifying selection at FT.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Tergemina, Emmanuel tergemina.e@gmail.com UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-83401
Date:	8 May 2017
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Außeruniversitäre Forschungseinrichtungen > MPI for Plant Breeding Research
Subjects:	Natural sciences and mathematics Life sciences Agriculture
Uncontrolled Keywords:	Keywords Language Flowering time, FLOWERING LOCUS T, cis-regulatory evolution, natural variation, allele-specific expression English
Date of oral exam:	10 July 2017
Referee:	Name Academic Title Coupland, George Prof. Dr. Höcker, Ute Prof. Dr. Albani, Maria Prof. Dr. Turck, Franziska Dr.
Funders:	Max Planck Society
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/8340