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The role of D-type cyclins in growth and development in Arabidopsis thaliana

Kilby, Joanne 2023. The role of D-type cyclins in growth and development in Arabidopsis thaliana. PhD Thesis, Cardiff University.
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The D-type cyclins (CYCDs) are key regulators of the G1/S transition of the cell cycle in plants, via the modulation of the activity of Cyclin Dependent Kinases (CDK). There are ten D-type cyclins in Arabidopsis made up of seven classes, whose expression is regulated in response to both external environmental and internal developmental signals. CYCD genes have differential and sometimes overlapping tissue specific expression patterns. Single cycd mutants cycd1;1, cycd2;1, cycd3;1, cycd3;2, cycd3;3, cycd4;1, cycd4;2, cycd5;1, cycd6;1, and cycd7;1 were analysed with respect to rosette area, epidermal cell area, cell density, stomatal density, and stomatal index. Using a CYCD multiple mutant approach further effects on cell division and the dependent processes of organ growth and development are explored. cycd mutants were combined to generate higher order cycd mutants. In addition to the previously published cycd3 triple, cycd mutant specific combinations are based on CYCD expression patterns, as in cycd1;1, cycd4;2, cycd6;1 triple and cycd2;1, cycd3;2, cycd7;1 triple and sequence similarity cycd2;1, cycd4;1, cycd4;2 triple created for this study. Progressive reduction of CYCD in higher order mutants in cycd3;1-3, cycd1;1 quadruple and cycd3;1-3, cycd6;1 quadruple, cycd3;1-3; cycd1;1, cycd6;1 pentuple, cycd3;1-3; cycd1;1, cycd2;1, cycd6;1 hextuple, cycd3;1-3; cycd1;1, cycd2;1, cycd4;2, cycd6;1 heptuple reveal additive, redundant and unique actions for individual CYCD genes. In the cycd3 triple mutant phenotype is subtle, mainly visible at the cellular level. Showing reduced cell proliferation with accompanied cell expansion enabling compensation of organ sizes. However, with additional reduction of CYCD activity in the cycd hextuple mutant macro fully penetrant phenotypes affecting lateral organ development are observed. At the cellular level there are additive effects on cell proliferation, with greater cell expansion observed relative to the cycd3;1-3 triple mutant. However, despite greater cell expansion, it is no longer sufficient to compensate the reduced cell numbers in organs, thus leading to smaller organs in the cycd hextuple mutant. Transcriptional analysis of these two cycd higher order mutants, reveals the effects of reducing overall CYCD expression and how this affects the entire G1/S gene network, including the expression of RBR, E2F, CDK, other cyclins and their inhibitors. ii This analysis reveals that the G1/S network is highly dynamic, at least at the transcript level. Furthermore, both S and M-phase genes are impacted by the reduced expression of CYCD. Gene ontology studies confirm CYCD as a key cell cycle regulator and expand our understanding of CYCD in relation to hormonal signalling. CYCDs respond differentially in terms of transcriptional activation to phytohormones, and we show that cycd mutants are affected in their hormone responses, both in tissue regeneration experiments and root growth assays. Furthermore, D-type cyclins influence the polar auxin transporter PIN1, impacting on auxin signalling. These observations indicate an important role for CYCD action linking cell division with morphogenetic signalling in plants.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Biosciences
Subjects: Q Science > Q Science (General)
Date of First Compliant Deposit: 6 November 2023
Last Modified: 22 Nov 2023 09:40

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