This report will focus on the maize aspects of the project. Postdoctorate Akio Kato has succeeded in producing tetraploids of diverse inbred lines using a nitrous oxide gas treatment shortly after fertilization of diploids. The gas blocks the first mitosis of development causing a doubling of chromosomes. When the kernels were mature, they were germinated and root tip chromosome counts identified the tetraploid individuals. This procedure allows the production of highly homozygous tetraploids of standard inbred lines. The four tetraploid inbreds that we are focusing on are A188, W22, B73 and Oh43. The generation of other tetraploids is in progress.
Dr. Kato had already developed a technique that is capable of generating triploid embryos that are associated with normal endosperm (Genome 42:154-157, 1999). This involves treatment of developing pollen with trifluralin. This compound blocks mitosis and when applied at the appropriate stage, generates high levels of diploid sperm. Using this technique, it will be possible to generate triploids of these four lines. Using stock 6, material has been generated that will yield maternal haploids of these lines. Thus 1-4x dosage series will soon be available for analysis.
Gene expression will be examined in the 1-4x dosage series to determine
the impact of allelic variation on the modulations of gene expression that
result from changes in ploidy. These materials will also be useful for
examining any epigenetic effects on gene expression or chromatin that might
be influenced by ploidy. Lastly, these materials will be used to examine
the molecular basis of heterosis. Hybrids and inbreds at the 2x to 4x levels
will be examined for global patterns of gene expression and for morphological
characteristics to gain an understanding of the relationship of dosage
dependent gene regulation and heterosis.
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