Isolation and characterization of SYN1, a RAD21-like gene essential for meiosis in Arabidopsis

The proper pairing, recombination, and segregation of chromosomes are centr al to meiosis and sexual reproduction. The syn1 mutation was previously ide ntified as a synaptic mutant in a T-DNA-tagged population of plants. SYN1 h as been isolated and found to exhibit similarity to Schizosaccharomyces pom be RAD21 and RADP1-like proteins, which are required for chromosome condens ation and sister chromatid cohesion during mitosis. Plants homozygous for s yn I are male and female sterile and show defects in chromosome condensatio n and pairing beginning at leptonema of meiosis I. Fragmentation of the chr omosomes was observed at metaphase I. Alternative promoters produced two SY N1 transcripts. One transcript was expressed at low levels in most tissues, whereas the other was expressed only in prebolting buds. DNA blot analyses suggest that Arabidopsis contains a small RAD21 gene family. Consistent wi th the DNA blot data, a second Arabidopsis RAD21-like gene has been identif ied. These results suggest that different RADP1-like proteins play essentia l roles in chromosome condensation and pairing during both meiosis and mito sis.