The Arabidopsis SKP1-LIKE1 gene is essential for male meiosis and may control homologue separation

The yeast and human SKP1 genes regulate the mitotic cell cycle but are not yet known to be required for meiosis. Nine Arabidopsis SKP1 homologues have been uncovered and are named ASK1 through ASK9. Here, we report the isolat ion and characterization of a male sterile Arabidopsis mutant and show that the mutant defect was caused by a Ds transposon insertion into the ASK1 ge ne. In the ask1-1 mutant, abnormal microspores exhibit a range of sizes. Fu rthermore, during mutant male meiosis, although homologous chromosome pairi ng appeared normal at metaphase I, chromosome segregation at anaphase I is unequal, and some chromosomes are abnormally extended. Therefore, in ask1-1 , at least some homologues remain associated after metaphase I. In addition , immunofluorescence microscopy indicates that the mutant spindle morpholog y at both metaphase I and early anaphase I is normal; thus, the abnormal ch romosome segregation is not likely caused by a spindle defect. Because the yeast Skp1p is required for targeting specific proteins for ubiquitin-media ted proteolysis, we propose that ASK1 controls homologue separation by degr ading or otherwise removing a protein that is required directly or indirect ly for homologue association before anaphase I.