Dynamics of chromosome organization during reproductive development – DYSCORD

Sexual reproduction in plants involves key developmental phases that first generate genetic distinct haploid spores during meiosis. After several rounds of division, the male and female spores eventually differentiate respectively into two male gametes (sperm cells) and two female gametes (egg cell, central cell). Double fertilization of the gametes then produces an embryo and its feeding tissue the endosperm that both develop inside a seed. During these phases, massive changes in cellular compartments, chromosome architecture and chromatin structure occur in a relatively short period of time. Unfortunately, these events take place deep inside the flower organs and in a limited number of cells, which complicates investigations and has left many questions unresolved for many years. Live imaging protocols have now been developed to observe reproductive cells during all key phases of plant reproduction (meiosis, gametogenesis, fertilization, embryogenesis) and greatly enhanced knowledge of some dynamic events. However, there is still a lack of tools to address any scientific question related to chromosome dynamics in living reproductive tissues. The recent development by partners of the project of the ANCHOR system - a new DNA-labelling system allowing live-cell imaging of a single locus in planta- provides an unprecedented possibility to fill the gap. ANCHOR comprises an OR protein fused to a fluorescent reporter that binds a ANCH target sequence, allowing robust live-cell imaging of a single locus in planta.
Taking advantage of state-of-the-art live-imaging approaches, The DYSCORD project aims to better understand two important reproduction steps: (i) parental chromosome recognition during meiosis and (ii) genomic imprinting in the endosperm. In work package 1, a collection of ANCHOR lines distributed throughout the Arabidopsis thaliana genome will be generated to allow the simultaneous observation of up to three unlinked single-copy loci in a single living nucleus. It should be noted that this collection will be accessible to the entire scientific community. In the second work package, we will study chromosome dynamics during meiosis, a step in which the parental chromosomes become tightly engaged one with another. We will use the ANCHOR lines to determine the dynamics of homologous chromosome interactions and compare the behaviour of different chromosomal regions either in wild type or in meiotic mutants. The work package 3 will focus on understanding how imprinted genes characterized by a monoallelic expression behave during endosperm development using live imaging. The dynamics of the distinct fluorescent ANCHOR-tagged parental alleles and their transcriptional activity will be simultaneously monitored using live RNA-based imaging technologies during endosperm development in wild type and in mutants that restore biallelic expression.
The results obtained in DYSCORD on A. thaliana will benefit the entire scientific community working in the field of meiosis and reproduction but will also generate several ground-breaking technical achievements in cell biology and live imaging, that should benefit the entire plant science community.