Plant J. 65(4):589-99 (Feb 2011)
Developmental changes in crossover frequency in Arabidopsis.
Toyota M, Matsuda K, Kakutani T, Terao Morita M, Tasaka M.


Parental genomes are generally rearranged by two processes during meiosis: one is the segregation of homologous chromosomes and the other is crossing over between such chromosomes. Although the mechanisms underlying chromosome segregation and crossing over are well understood because of numerous genetic and molecular investigations, their contributions to the rearrangement of genetic information have not yet been analysed at a genome-wide level in Arabidopsis thaliana. We established 343 CAPS or SSLP markers to identify polymorphisms between two different Arabidopsis ecotypes, Col and Ler, which are distributed at an average distance of approximately 400kb between pairs of markers throughout the entire genome. Using these markers, crossover frequencies and chromosome segregation were quantified with respect to sex and age. Our large-scale analysis demonstrated that:

  1. crossover frequencies during pollen formation were 1.79 and 1.37 times higher than those during megaspore formation in early and late flowers, respectively (P<0.001);
  2. the crossover frequencies during pollen formation were not significantly different between early and late flowers of main shoots (P>0.05), whereas the frequencies increased 1.30 times with shoot age during megaspore formation (P<0.001);
  3. the effect of aging depended on the developmental age of the individual shoot rather than on the age of the whole plant; and
  4. five chromosomes were randomly selected and mixed during meiosis.

Our data using lateral shoots and LD/SD conditions suggest that developmental age rather than the absolute age of whole plants affects crossover frequency (Table 6). Therefore, the bolting of each individual inflorescence might define time zero for the internal clock that determines age with respect to the regulation of crossover frequency. Arabidopsis thaliana is annual, but many higher plants are perennial. It would seem appropriate for perennial plants if individual shoots determine the timing for changes in crossover frequencies on the basis of bolting. Whether and how this strategy could also be useful for annual species is an interesting question that remains to be answered.