Seminars

The foundation of sexual reproduction is the formation of gametes with half the genomic DNA content of a somatic cell. This reduction in genomic content is accomplished through meiosis that, in contrast to mitosis, comprises two subsequent chromosome segregation steps without an intervening S-phase. In addition, meiosis generates new allele combinations through the compilation of new sets of homologous chromosomes and the reciprocal exchange of chromatid segments between homologs. Hence, understanding of meiosis is not only of fundamental interest for biology but also for plant breeding and agriculture. In our team, we study how entry and progression through meiosis is controlled. Particular focus is on the cell-cycle machinery and our data show that CYCLIN-DEPENDENT KINASE A;1 (CDKA;1), the major regulator of mitosis in Arabidopsis, also plays a key role in orchestrating chromosome behavior in meiosis. Using a series of weak loss-of-function alleles of CDKA;1 in combination with a newly established live cell imaging system of meiosis, we find that plants with very little Cdk activity are sterile due to several severe meiotic defects, including a failure of chromosomes to synapse. Subsequently, we identify that the chromosome axis protein ASYNAPTIC 1 (ASY1) is a phospho-target of CDKA;1 action and show that phosphorylation of ASY1 by CDKA;1 is key for the dynamic assembly of the chromosome axis. Moreover, these data provide a glimpse at the molecular mechanisms how the complex steps of meiosis can be put into order.