Columbia, Missouri
University of Missouri
Functional genomics of plant polyploids --Birchler, JA The NSF genome project "Functional Genomics of Plant Polyploids" seeks to understand the impact of ploidy on gene expression, the genomic changes that accompany newly formed polyploids and the molecular basis of heterosis with special emphasis on its interrelationship with ploidy. The group is composed of Tom Osborn, PI, University of Wisconsin, Jeff Chen, Texas A and M, Luca Comai, University of Washington, Rebecca Doerge, Purdue University, Rob Martienssen, Cold Spring Harbor, and Jim Birchler, University of Missouri. The species being examined are Arabidopsis, Brassica and Corn (The ABCs).

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.

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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