Factors Underlying Restricted Crossover Localization in Barley Meiosis

Abstract

Meiotic recombination results in the formation of cytological structures known as chiasmata at the sites of genetic crossovers (COs). The formation of at least one chiasma/CO between homologous chromosome pairs is essential for accurate chromosome segregation at the first meiotic division as well as for generating genetic variation. Although DNA double-strand breaks, which initiate recombination, are widely distributed along the chromosomes, this is not necessarily reflected in the chiasma distribution. In many species there is a tendency for chiasmata to be distributed in favored regions along the chromosomes, whereas in others, such as barley and some other grasses, chiasma localization is extremely pronounced. Localization of chiasma to the distal regions of barley chromosomes restricts the genetic variation available to breeders. Studies reviewed herein are beginning to provide an explanation for chiasma localization in barley. Moreover, they suggest a potential route to manipulating chiasma distribution that could be of value to plant breeders.

Synaptonemal complex extension from clustered telomeres mediates full-length chromosome pairing in Schmidtea mediterranea

“…Nonetheless, the initiation of SC formation in subtelomeric regions at the bouquet stage and the early localization of recombination proteins to these regions also have been seen in barley (62,63). However, as zygotene proceeds, numerous medial sites of SC initiation are observed also.…”

Next generation breeding

“…The two distal regions were characterized by an elevated meiotic recombination rate (of 0.60 and 0.96 cM/Mb) which was clearly distinct from the low meiotic recombination rate (of 0.05 cM/Mb) observed in the large proximal region spanning the centromeric-pericentromeric area [115]. Different studies are underway to understand the mechanisms (and the genes) regulating the formation of crossovers to allow the control of their frequency and position [116]. For example, it was shown that a mutation of the Arabidopsis FANCM gene results in a substantial increase of meiotic crossover formation, without negative impacts on chromosome stability [117].…”

Epigenetic control of meiotic recombination in plants

“…Understanding meiotic recombination will be important as it has a significant influence on genetic diversity and speciation, for example, axis proteins have been implicated in the evolution of polyploid Arabidopsis species [137,138]. In addition, knowledge of how crossovers are controlled will allow this process to be manipulated in useful ways in crop species [6].…”

“…The precise advantage that sexual reproduction confers is debated, though its advantages must be strong and general as it is maintained in unicellular and multicellular species of variable population sizes and ecologies [4,5]. It is also important to understand meiotic recombination in the context of agricultural breeding, where homologous recombination can be restricted to specific chromosomal regions and thereby limit use of crop genetic variability [6].…”