THE ROLE OF THE AMEIOTIC1 GENE IN THE INITIATION OF MEIOSIS AND IN SUBSEQUENT MEIOTIC EVENTS IN MAIZE

Understanding the initiation of meiosis and the relationship of this e vent with other key cytogenetic processes are major goals in studying the genetic control of meiosis in higher plants. Our genetic and struc tural analysis of two mutant alleles of the ameiotic1 gene (am1 and am 1-praI) suggest that this locus plays an essential role in the initiat ion of meiosis in maize. The product of the ameiotic1 gene affects an earlier stage in the meiotic sequence than any other known gene in mai ze and is important for the irreversible commitment of cells to meiosi s and for crucial events marking the passage from premeiotic interphas e into prophase I including chromosome synapsis. It appears that the p eriod of ameiotic1 gene function in meiosis at a minimum covers the in terval from some point during premeiotic interphase until the early zy gotene stage of meiosis. To study the interaction of genes in the prog ression of meiosis, several double meiotic mutants were constructed. I n these double mutants (i) the ameiotic1 mutant allele was brought tog ether with the meiotic mutation (afd1) responsible for the fixation of centromeres in meiosis; and with the mutant alleles of the three meio tic genes that control homologous chromosome segregation (dv1, ms43 an d ms28), which impair microtubule organizing center organization, the orientation of the spindle fiber apparatus, and the depolymerization o f spindle filaments after the first meiotic division, respectively; (i i) the afd1 mutation was combined with two mutations (dsy1 and as1) af fecting homologous pairing; (iii) the ms43 mutation was combined with the as1, the ms28 and the dv1 mutations; and (iv) the ms28 mutation wa s combined with the dv1 mutation and the ms4 (polymitotic1) mutations. An analysis of gene interaction in the double mutants led us to concl ude that the ameiotic1 gene is epistatic over the afd1, the dv1, the m s43 and the ms28 genes but the significance of this relationship requi res further analysis. The afd gene appears to function from premeiotic interphase throughout the first meiotic division, but it is likely th at its function begins after the start of the ameiotic1 gene expressio n. The afd1 gene is epistatic over the two synaptic mutations dsy1 and as1 and also over the dv1 mutation. The new ameiotic()-485 and lepto tene arrest()-487 mutations isolated from an active ROBERTSON's Mutat or stocks take part in the control of the initiation of meiosis.