student profile: Mr Jacob Downs


Thesis work

Thesis title: The effect of ARF1 and ARF2 mutations on Arabidopsis developmental phenotype

Supervisors: Brian JONES , Penny SMITH

Thesis abstract:

Auxin Response Factors (ARF) are a diverse group of proteins that help regulate auxin responsive genes responsible for numerous developmental processes. Auxin response factor proteins can act as activators or repressors of auxin responsive genes by binding to Auxin Response cis-acting Elements (AuxREs) located in the promoters. Auxin response factor proteins that act as activators can be repressed by the Auxin/Indole-3-Acetic Acid repressor (Aux/IAA). Auxin is a hormone that regulates ARF proteins. Auxin performs this process by interacting with Transport Inhibitor Response1/Auxin Signalling F-Box Complex (TIR1/AFB). This interaction leads to the ubiquinylation of the Aux/IAA repressor. Ubiquinylation of the Aux/IAA repressor results in its proteolytic degradation, reactivating the ARF activators and bound gene. Auxin response factor repressors do not require Aux/IAA and are suggested to simply compete with ARF activators for AuxRE binding sites. Some ARF activators lack the Aux/IAA binding site and cannot be repressed. The ARF proteins 1 and 2 are two repressor ARF proteins that play pivotal roles in plant development. Auxin response factor 2 levels are regulated by ethylene and light levels along with gibberellins. Auxin response factor 1 has been found to increase the levels of Aux/IAA thereby acting as a repressor. Mutants of ARF2 have late aging, flowering, rosette leaf senescence, floral organ abscission and silique ripening. Auxin response factor 2 mutants also have delayed apical hook opening and enlarged seed, stems and cotyledons. This suggests that ARF2 is involved in numerous life stages of plants. Despite not yielding phenotypes on their own, mutations of the ARF1 protein appear to enhance the phenotypes generated from ARF2 mutations. Interestingly, ARF2 may not supress auxin responsive genes in the typical manner and may partake in a unique mechanism. This project will entail the phenotyping and genotyping of Arabidopsis thaliana wild-type and ARF1 and ARF2 mutants at varous devlopmental stages to address the individual and synogistic functions of these proteins. Auxin response and regulation is an incredibly important part of plant development. Knowledge gained from studying auxin response will provide a deeper understanding of the genetics and biochemistry of plant embryonic, juvenile and adult development. Ultimately, this knowledge could be applied to agriculture to improve plant growth and yield for food and biofuel production.

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