Sexually reproducing organisms rely on the precise reduction of chromosome number during a specialized cell division called meiosis. Whereas mitosis produces diploid daughter cells from diploid cells, meiosis generates haploid gametes from diploid precursors. The molecular mechanisms controlling chromosome transmission during both divisions have started to be delineated. This review focuses on the four fundamental differences between mitotic and meiotic chromosome segregation that allow the ordered reduction of chromosome number in meiosis: (1) reciprocal recombination and formation of chiasmata between homologous chromosomes, (2) suppression of sister kinetochore biorientation, (3) protection of centromeric cohesion, and (4) inhibition of DNA replication between the two meiotic divisions.

Separase is essential for homologous chromosome disjunction during meiosis I. Proteolytic cleavage, presumably of Rec8, might be a common trigger for the first meiotic division in eukaryotic cells. Cleavage of proteins other than REC-8 might be necessary to render the eggshell impermeable to solutes.

Cohesion between sister chromatids mediated by a multisubunit complex called cohesin is established during DNA replication and is essential for the orderly segregation of chromatids during anaphase. In budding yeast, a specialized replication factor C called RF-CCtf18/Dcc1/Ctf8 and the DNA-polymerase-α-associated protein Ctf4 are required to maintain sister-chromatid cohesion in cells arrested for long periods in mitosis. We show here that CTF8, CTF4 and a helicase encoded by CHL1 are required for efficient sister chromatid cohesion in unperturbed mitotic cells, and provide evidence that Chl1 functions during S-phase. We also show that, in contrast to mitosis, RF-CCtf18/Dcc1/Cft8, Ctf4 and Chl1 are essential for chromosome segregation during meiosis and for the viability of meiotic products. Our finding that cells deleted for CTF8, CTF4 or CHL1 undergo massive meiosis II non-disjunction suggests that the second meiotic division is particularly sensitive to cohesion defects. Using a functional as well as a cytological assay, we demonstrate that CTF8, CHL1 and CTF4 are essential for cohesion between sister centromeres during meiosis but dispensable for cohesin's association with centromeric DNA. Our finding that mutants in fission yeast ctf18 and dcc1 have similar defects suggests that the involvement of the alternative RF-CCtf18/Dcc1/Ctf8 complex in sister chromatid cohesion might be highly conserved.

As sessile organisms that are unable to escape from inhospitable environments, plants are at the mercy of the elements. Nonetheless, plants have managed to adapt, evolve and survive in some of the harshest conditions on earth. The FEBS Workshop ‘Adaptation Potential in Plants’, held at the Gregor Mendel Institute of Molecular Plant Biology, Vienna, Austria from 19 to 21 March 2009, provided a forum (including 18 invited talks, 8 selected short talks and 69 posters) for about 100 plant biologists from 32 countries, working in the diverse fields of genetics, epigenetics, stress signalling, and growth and development, to come together and discuss adaptation potential in plants at all its levels.