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Title: Mechanisms of plant cell proliferation control by light, during leaf initiation and acclimation to high light irradiance
Author: Mohammed, Binish
ISNI:       0000 0004 8499 4304
Awarding Body: Royal Holloway, University of London
Current Institution: Royal Holloway, University of London
Date of Award: 2017
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Plant growth is continuously shaped by environmental and internal cues, pivotal among which are light and energy status. In plants such as Arabidopsis thaliana, light drives leaf initiation and development. Control of proliferation is needed for leaf initiation and growth. Cessation of proliferation-dependent growth results in differentiation, growth that is accompanied by endoreduplication/cell expansion. To understand how the transcription factor E2FB controls proliferation I examined, at the cellular and gene expression level, lines with modified E2FB function. I show that E2FB has other developmental functions, apart from regulating the duration of proliferation. Dissection of the shoot apex during leaf initiation upon dark to light transfer of seedlings (deetiolation) previously revealed key gene signatures involved in organ initiation. To understand how light regulates proliferation-dependent growth we first noted a close integration between expression of cell cycle genes, phosphorylation state of the core cell cycle RETINOBLASTOMA-RELATED protein, light signalling pathways and carbon availability. I then monitored growing leaf primordia upon transfer to dark and return to light. I observed growth arrest in the dark, its reversal by light being accompanied by similar gene expression signatures to those during light-driven de novo leaf initiation, namely a reversal of an 'energy starvation' state, a transient shift of hormone responses from auxin to cytokinin, and coordinated build-up of ribosomes. Leaves that acclimate to high light have a multi cell layered palisade but fail to show this anatomy in chloroplast-defective cells of variegated mutants. To understand a possible link between energy and proliferation-dependent growth I monitored mitotic growth and cell ploidy level. My findings suggest that high light causes leaf cell proliferation-dependent growth to intensify but terminate sooner. Overall I have introduced an easily-tractable cell synchronisation assay, and provided evidence for the integration of light signals controlling proliferation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available