Universiteit Leiden

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Dissertation

The role of the Arabidopsis AHL15/REJUVENATOR gene in developmental phase transitions

This thesis describes the functional analysis of the Arabidopsis AHL15 gene.

Author
Omid Karami
Date
14 November 2017

This thesis describes the functional analysis of the Arabidopsis AHL15 gene. We showed that AHL15 and plays major roles in directing plant cell totipotency. Furthermore, our data show that AHL15 has a role in opening of chromatin, leading to endomitosis and polyploidy in embryonic cells and that AHL15 overexpression can lead to polyploid SEs and plants, probable by endomitotic events caused by incomplete chromatin condensation during cell division. More detailed analyses revealed that AHL15 is not specifically involved in the embryogenesis program, but that, surprisingly, the protein rather is involved in post embryonic development. Our analyses in Arabidopsis and tobacco showed that AHL15act as suppressors of developmental phase changes. In Arabidopsis, reduced AHL15 expression coincided with a faster progression from the vegetative to the reproductive phase. By contrast, AHL15 overexpression delayed the vegetative to reproductive phase change in both Arabidopsis and tobacco, causing some axillary meristems to be maintained in the vegetative phase, thereby allowing polycarpic development in these monocarpic annuals. By using RNA sequencing analysis, an extensive reprogramming of the transcriptome detected after AHL15 activation. Rapid decondensation of heterochromatin was observed after AHL15 activation, indicating that the global reprogramming of the transcriptome by AHL15 might at least in part be caused by extensive modulation of the chromatin configuration.