Universität zu Köln

Bertran Garcia de Olalla, Enric ORCID: 0000-0003-2987-1849 (2023). Functions of MICRORNA172 and APETALA2-LIKE genes during floral transition at the shoot apical meristem. PhD thesis, Universität zu Köln.

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Abstract

The integration of environmental and internal signals controls floral transition at the shoot apical meristem (SAM), which contains one of the stem-cell niches that generate aerial organs. During floral transition, the identity of the SAM changes from a vegetative meristem that initiates leaf primordia at its periphery, to an inflorescence meristem that produces floral primordia. Five MICRORNA172 (MIR172) genes encode microRNA172 (miR172), which is a small RNA molecule that accumulates at the SAM during floral transition and promotes flowering by repressing the expression of the APETALA2-LIKE (AP2-LIKE) genes. MIR172A, MIR172B and MIR172D are expressed at the SAM during floral transition, and their onset of expression is earlier under inductive long days compared to short days. Notably, miR172 is also a positive regulator of inflorescence meristem size, largely by down-regulating the expression of the positive SAM area regulator AP2. Considering the earlier expression of MIR172 genes at the SAM under inductive long days, the genetic relationships between the main components of the photoperiodic pathway and MIR172 and AP2-LIKE genes were characterised. In the second chapter of this dissertation, it is shown that although the regulation of flowering time by MIR172 and AP2-LIKE genes is influenced by inductive photoperiods, these genes also regulate flowering time in a photoperiod-independent manner. In light of the negative role of miR172 and the positive role of APETALA2 (AP2) in the regulation of inflorescence meristem size, the involvement of MIR172 and AP2 genes in the enlargement of the SAM during floral transition was explored. The results in the third chapter of this dissertation show that AP2 is a positive regulator of shoot meristem size during floral transition and is essential for changes in SAM size. A genetic relation between AP2 and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1, which encodes a MADS domain transcription factor, was proposed as a mechanism that couples changes in SAM morphology and floral transition. The involvement of MIR172 genes in the regulation of flowering time was analysed by comparing the transcriptome profile of dissected plant apices from Col-0 vs. mir172 mutants. The constant mRNA levels of TARGET OF EAT 2, an AP2-LIKE gene, are a candidate main alteration that underlies the late-flowering of mir172 mutants. The transcription factor TOE2 was then characterised and a genetic relation between TOE2, AP2 and SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE 4 is proposed. This work provides a framework for understanding the positive role of miR172 in the regulation of flowering time by repressing AP2-LIKE genes and constitutes evidence for the involvement of flowering-time regulators in the changes of SAM morphology during floral transition.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Bertran Garcia de Olalla, Enric ebertran@mpipz.mpg.de orcid.org/0000-0003-2987-1849 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-713768
Date:	13 June 2023
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Außeruniversitäre Forschungseinrichtungen > MPI for Plant Breeding Research
Subjects:	Natural sciences and mathematics
Uncontrolled Keywords:	Keywords Language Plant Developmental Biology English Shoot Apical Meristem English Flowering time English Arabidopsis thaliana English APETALA2 UNSPECIFIED MICRORNA172 UNSPECIFIED
Date of oral exam:	28 September 2023
Referee:	Name Academic Title Coupland, George Prof. Dr. Kopriva, Stanislav Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/71376