Characterising GIGANTEA interactors: the BELL-LIKE HOMEODOMAIN 3 and BELL-LIKE HOMEODOMAIN 10 proteins

ABSTRACT The ability to detect and respond to environmental signals is fundamental in coordinating floral induction in plants to favourable conditions. An important flowering time cue is day length and it is proposed that light signals are perceived and measured by an interaction between photoreceptors and an internal pacemaker, the circadian clock. The control of flowering has been best characterised in the model plant Arabidopsis thaliana L. Heynh (Arabidopsis). The GIGANTEA (GI) gene has a complex role in both the promotion of flowering in response to photoperiod and the regulation of the circadian clock. The expression of GI is under circadian control and is affected by day length, light quality and temperature changes. The GI protein is also circadian regulated and is actively degraded in the dark. The biochemical function of GI is unknown and one method to elucidate the role of this protein is to identify protein interactors. The aim of this thesis project was to characterise proteins that interacted with GI. Previously, the BELL-LIKE HOMEODOMAIN 3 (BLH3) protein was identified as a putative GI protein interactor. As part of this thesis work, yeast 2-hybrid and in vitro pull down assays were utilised to confirm the interaction between GI and BLH3. Sequence and phylogenetic analyses were used to further examine the BELL family of proteins. The BELL-LIKE HOMEODOMAIN 10 (BLH10) protein was found to be closely related to BLH3 and also interacted with GI. Reverse 2-hybrid assays were used to determine the regions or domains within the GI, BLH3 and BLH10 proteins required to mediate protein interactions. Expression assays established that the BLH3 and BLH10 transcripts were present throughout plant tissues and times of development. Further analyses revealed that BLH3 and BLH10 are not directly regulated by the circadian clock. The results of GFP expression assays demonstrated that the BLH3 protein is localised to the nucleus in plant cells. Transgenic blh3 and blh10 mutant plants were identified and analysed for flowering and light response phenotypes. BLH3 and BLH10 do not function with GI in the photoperiodic pathway to control flowering, yet the blh3 and blh10 mutants do have a flowering phenotype in short day conditions. Like gi, the blh3 and blh10 mutants exhibited exaggerated hypocotyl elongation in response to red and low light conditions. These results are suggestive of a role for BLH3, BLH10 and GI in flowering and deetiolation responses to specific light conditions in plants.

Name thesis:degree_name

PhD

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Biological Sciences

Grantor dc:publisher

ResearchSpace@Auckland

Year dc:date.issued

2006

Author dc:creator

• Milich, Raechel Jean

Advisors dc:contributor.advisor

• Jo Putterill
• Richard Gardner

• flowering, Arabidopsis, protein interaction
• plant molecular biology

Statement dc:rights

• Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

Licence dc:rights.uri

• https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/2292/417

OAI identifier oai:identifier

oai:researchspace.auckland.ac.nz:2292/417