Characterizing the microtubule-associated function of the B1-type cyclins in Arabidopsis thaliana and towards live cell imaging of meiosis in A. lyrata and A. arenosa

In mitosis, a precise duplication and equal distribution of the genomic DNA between daughter cells is essential for genome stability and growth. For such a precise division, eukaryotes make use of a set of cytoskeletal arrays, which are composed mainly of microtubule filaments. Because plant cells cannot move as opposed to animal cells, plants rely on a precise cell division site determination for organ growth and patterning. Accordingly, plants have developed specific microtubule-based structures for cell divisions, such as the preprophase band (PPB) and the phragmoplast. The PPB is a band of microtubules that forms before division at the cell cortex around the equator of the nucleus. It is known to mark the periphery of the division plane and anchor proteins that remain there throughout cell division, acting as fiducial markers. The spindle, which appears after the PPB has disassembled and the nuclear envelope has broken down, is essential for accurate sister chromatid segregation. After sister chromatids have been segregated, the phragmoplast forms, which guides accurate membrane and cell wall formation between the two daughter nuclei, ensuring a successful cell division. The progression of the cell cycle is tightly regulated by cyclins and cyclin-dependent kinases (CDKs). They act together to phosphorylate a plethora of substrates, with specificity provided by both the cyclin and CDK partner. Phosphorylation can promote rapid changes in protein activity, which is in accordance with the significant changes in microtubule conformation throughout cell division. Here, in the first chapter, I have characterized the function of the five-member CYCLIN B1 group in Arabidopsis thaliana. I show that the function of B1-type cyclins is highly redundant and tissue-dependent. Interestingly, mutants for B1-type cyclin members have compromised microtubule arrays, including misplaced and double PPBs, as well as chromosome laggards in metaphase and abnormal phragmoplasts. I further reveal that B1-type cyclins, especially ...