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PhD theses defended at IPS2

Ph D theses recently defended at IPS2


Characterization of a new dominant andromonoecy-causing locus in Cucumis melo

Keywords: Sex determination, flower development, cucurbits, andromonoecy, monoecy, ethylene.

In plants, sex determination leads to the development of unisexual flowers from an originally bisexual floral meristem. This favorable evolutionary mechanism has resulted in enhancement of outcrossing and promotion of genetic variability. In melon, different sexual forms are controlled by the identity of the alleles at three major loci androecious (A), gynoecious (G) and andromonoecious (M). Previously, it was demonstrated that the M gene encodes an ethylene biosynthesis enzyme, CmACS7, which represses stamen development in female flowers. CmACS7 loss of function leads to stamen growth and consequently to an andromonoecious phenotype. During her PhD thesis, within the FLOCAD team at IPS2, Dali RACHID investigated how the cloned sex genes control unisexal flower development.  Using a combination of genetic, genomic and cellular biology approaches, she identified a gene network leading to unisexual flower development.

December 4, 2020

Thesis supervisor: Dr. Adnane Boualem



Regulation of the symbiotic nitrogen-fixing nodulation by signalling peptides in Medicago truncatula

Keywords: peptides, symbiosis, development, signalling, root, nodulation.

In legumes, the root system is not only able to form lateral roots, but also develops new organs, the atmospheric nitrogen-fixing nodules, thanks to a symbiosis with bacteria, called rhizobia, when the soil is poor in mineral nitrogen. The formation and maintenance of these nodules are energy-consuming and must therefore be strictly regulated by the plant in order to inhibit or promote nodulation according to its nitrogen needs. Peptide hormones of the CLE (“Clavata3 (CLV3) / Embryo Surrounding Region”) and CEP (“C-terminally Encoded Peptide”) families, produced in roots, have in particular been identified as respectively playing a systemic (at long distance ) negative or positive role on nodulation, from the aerial parts. Their action rely on the SUNN (“Super Numeric Nodules”) and CRA2 (“Compact Root Architecture 2”) receptors, respectively. The main goal of Pierre GAUTRAT’s Ph. D Thesis (SILEG team at IPS2) was to understand how signaling peptides regulate nodulation both locally and systemically. To this end, two objectives were defined: 1) to identify molecular mechanisms associated with the systemic CLE / SUNN and CEP / CRA2 signaling pathways regulating nodulation; 2) to characterize new CLE peptides regulating nodulation. Results obtained allowed demonstrating that a common actor acting downstream of the CLE / SUNN and CEP / CRA2 pathways is the microRNA miR2111. This miRNA is produced in shoots and regulated antagonistically by the two systemic pathways and cleaves transcripts of TML (“Too Much Love”) genes in roots, thereby controlling the number of nodules formed depending on nitrogen availability and pre-existing nodules. Furthermore, the activity of a CLE peptide whose expression is induced in the root epidermis under symbiotic conditions, CLE37, is required to modulate root development in response to rhizobia, inhibiting the growth of main roots and increasing their diameter. The recruitment of this CLE signaling peptide could thus help accommodating root development to support the needs of the nitrogen-fixing symbiosis.

December 17, 2020

Thesis supervisor: Dr. Florian Frugier


Richard RIGO

Role of the NSR-ASCO ribonucleoprotein complex in plant development

Keywords: plant development, non-coding RNA, alternative splicing.

Plants are sessile organisms which have to constantly adapt to the stresses they encounter. They modulate the transcription of a large panel of genes to change their cellular properties: some transcripts encode proteins, others remain under the form of non-coding RNAs. Long non-coding RNAs (lncRNAs) are a class of transcripts known to participate in the adaptation to stresses. For example, the lncRNA ALTERNATIVE SPLICING COMPETITOR (ASCO) interacts with specific nuclear proteins, the NUCLEAR SPECKLE RNA-BINDING PROTEINS (NSRs). Their interaction leads to changes in the abundance of specific transcripts, modulating root initiation and development. This study aimed to understand the role of this interaction within plant development at a global level. We showed that NSRs and ASCO play a role in plant immunity, by modulating the expression of specific transcripts. Moreover, the lncRNA ASCO seems to be also involved in the response to temperature changes, thus being a putative integrator of multiple stresses within the plant.

June 18, 2021

Thesis supervisors: Dr. Céline Charon and Dr. Martin Crespi