45003:

Isolation and characterization of RAD21-like genes essential for meiosis and mitosis in Arabidopsis.

Authors:	Makaroff, Christopher, A.(A)Bai, Xuefang(A)Fugui, Dong(A)Cai, Xue(A)Peirson, Brenda, N.(A)
Affiliations:	(A): Department of Chemistry and Biochemistry, Miami University
Presenter:	Makaroff, Christopher A., makaroca@muohio.edu

Meiosis consists of a complex series of processes that are central to sexual reproduction. During leptonema of meiotic prophase I newly replicated chromosomes condense, homologous chromosomes align, and the synaptonemal complex, an elaborate proteinaceous structure that holds homologs closely aligned along their lengths, is formed. At pachynema, nonsister chromatids of the paired chromosomes recombine forming chiasmata, which become visible as the chromosomes start to desynapse during diplonema. During meiosis I, cohesion between sister chromosomes facilitates their orientation and the proper attachment of the kinetochores to spindle microtubules. After anaphase I, sister chromosome cohesion is released in preparation for the second meiotic division. Therefore, the formation and proper maintenance of sister chromatid cohesion is essential for the proper alignment and segregation of chromosomes during meiosis. As part of studies to better understand meiosis in plants, we have characterized a number of T-DNA-tagged, male-sterile mutants of Arabidopsis. Cytological studies on one line, syn1 which is male and female sterile, indicated that it produced polyads containing up to eight microspores with variable amounts of DNA. Microsporocytes in syn1 plants show defects in chromosome condensation and pairing beginning at leptonema of prophase I. Fragmentation of chromosomes is observed at metaphase I. SYN1 has been isolated and found to exhibit similarity to S. pombe RAD21 and RAD21-like proteins, which are required for chromosome condensation and sister chromatid cohesion during mitosis. Alternative promoters/splicing results in the production of two SYN1 transcripts. One transcript is expressed at low levels in most tissues, while the other is expressed only in prebolting buds. Additional Arabidopsis RAD21-like genes (SYN2 and SYN3) have been identified and are being analyzed. RAD21-proteins exhibit the highest sequence conservation at their amino- and carboxy-termini. Very little sequence conservation is observed in the middle of the proteins; however, this region is hydrophilic and relatively acidic in all the proteins. Transcripts for SYN2 are present at low levels in all tissues, suggesting that it may be involved in chromosome condensation and cohesion during mitosis. Analysis of the Arabidopsis SYN genes is providing insight into chromosome condensation, pairing and cohesion during meiosis and mitosis.