Organisation dynamics and pairing of the telomeres and sub-telomeres in Arabidopsis meiosis

The primary role of the telomeres is to stabilise the ends of the eukaryotic chromosome, but it is apparent that the telomere also has a role in the universal pathway of meiosis, a specialised type of cell division. Most living organisms, from animals to plants reproduce sexually. Briefly, during meiosis the chromosomes are copied, followed by 2 successive chromosome divisions. During the pathway to the first division the pairs of chromosomes find each other and are held together by exchanging part of their chromosomes with their partner, a process known as recombination, until the first division where they are separated. The second division is similar to mitosis. There are many outstanding questions in meiosis for example how do the chromosomes manage to pair and recombine? We think that the telomeres are important in early meiosis to move the chromosomes around until they are closely aligned with their partner. This grant proposal is concerned with understanding more about the organisation and pairing of the telomeric regions in meiosis as well as developing an imaging system to help elucidate the dynamics of telomere behaviour using the model plant, Arabidopsis. There are a number of advantages of using this model plant; for example it only has 5 pairs of chromosomes, its chromosomes have been sequenced and mutants affecting the progression of meiosis and telomere maintenance have been identified. We will use these significant advantages offered by Arabidopsis, in particular that there are only 5 pairs of chromosomes, to elucidate these fundamental aspects of telomere biology. Understanding of the meiotic process has been greatly advanced by biochemical, cytological and genetic analyses of the budding yeast, Saccharomyces cerevisiae and increasingly in a number of other model organisms. Arabidopsis is recognised as an excellent system for analysis of plant meiosis, and one of the aims of the current research is to understand whether and to what extent meiotic processes and controls are conserved across both plants and animals. Inclusion of a plant model is very important, particularly if we are to transfer our knowledge to crop species and traits related to their fertility. It is likely to provide support for key general principles; because meiosis is a universal process, information regarding telomere behaviour in plants is likely to be relevant to general telomere biology and therefore reproduction and telomere function in humans.

The ends of linear eukaryotic chromosomes are protected from degradation by a complex specialised structure, the telomere, consisting of a repeated DNA motif, and its associated DNA binding proteins. The role of these proteins is to maintain and regulate the telomeres. Degradation of the telomeres leads to loss of genetic material and is linked to a cell senescence and apoptotic pathway. Although the telomere has a primary role in protecting the ends of the chromosomes there is evidence that it also has a role in chromosome movement and progression during the meiotic pathway. This project is concerned with understanding how the telomeres function during meiosis. Meiosis plays a central role in the life cycle of all sexually reproducing organisms, and understanding meiosis underpins our knowledge of fertility and genetic variability. Amongst the outstanding questions in meiosis is how the homologous chromosomes find each other and subsequently synapse and recombine during meiotic prophase. An early event in prophase I is the movement and clustering of the telomeres at the nuclear membrane, to form the so-called 'bouquet', that precedes chromosomal pairing and synapsis. In Arabidopsis we do not observe a bouquet and we have already shown that homologous telomeres are paired at an early stage in the meiotic pathway, before movement to the nuclear membrane. We will investigate how the Arabidopsis telomeres are organised throughout early meiosis at the ultra structural level with the electron microscope, investigate the nature of homologue pairing and develop imaging techniques to study the dynamics of telomere behaviour in vivo. We will use the significant advantages offered by Arabidopsis as a plant model for elucidating these fundamental aspects of telomere biology. Inclusion of a plant model is very important for meiotic research, particularly if we are to transfer our knowledge of Arabidopsis meiosis to crop species and their fertility.