Chromosome synapsis in Arabidopsis: analysis of the transverse filament protein ZYP1 reveals novel functions for the synaptonemal complex

With respect to history, plants have provided an ideal system for cytogenetical analysis of the synaptonemal complex (SC). However, until recently, the identification of the genes that encode the SC in plants has proved elusive. In recent years, Arabidopsis thaliana was developed as a model system for plant meiosis research. As a result, there was substantial progress in the isolation of meiotic genes and this has recently led to the isolation of the first plant SC gene, ZYP1. The ZYP1 gene encodes a transverse filament (TF) protein that is predicted to have structural similarity to TF proteins found in other organisms. Analysis of plants deficient in ZYP1 expression has provided important insights into the function of the SC in plants. Loss of ZYP1 has only a limited effect on the overall level of recombination. However, it is associated with extensive nonhomologous recombination leading to multivalent formation at metaphase I. This phenomenon was not previously reported in other organisms. It is important to note that cytological analysis of the ZYP1 deficient lines indicates that SC formation is not required for the imposition of crossover interference.