Project Documentation & Protocols: Maize Gene Discovery Project: Education:
What's Next for Maize Genetics?

Contents: Maize Gene Discovery | The Challenge of Maize Genetics | Why Discover Maize Genes? | Finding Genes
Linking Genes to Function | Creating Databases | Building a Storehouse | Accomplishments | What's Next? | Glossary

By providing multiple tools and oodles of data for future research, the Maize Gene Discovery Project changes researchers' modus operandi. Instead of doing everything themselves . growing their own mutants, manufacturing their own DNA libraries and microarrays, inventing and testing their own bioinformatics tools -- they can now shop online for exactly what they need . for free.

Already, the MGDP has distributed hundreds of seed stocks, more than one thousand microarrays; and more than 1500 ESTs for use as probes to find genes of interest. The team expects thousands of requests to arrive over the next few years from the more than 40 publicly-funded maize genomics projects underway at institutions across the nation (see MaizeDB projects page: http://www.agron.missouri.edu/zprojects.html) and the thousands of individual researchers working with maize around the world.

Prime examples of such genomics projects with potential agricultural importance include the following:

MGDP team member Brian Larkins has joined researchers at the University of Florida in a new project to identify genes that change the quality of maize endosperm. The endosperm is what "explodes" in popcorn, and it is the major storage depot of protein, lipid, and carbohydrate in maize seeds. Using gene mutations, corn breeders have perfected sweet corn that remains sweet after picking, fluffy popcorn, and animal feed with a better balanced protein content. Storage proteins, called zeins, are the most abundant proteins in the seed and the principal determinant of its nutritional value. Zeins often lack several nutrients essential to human and livestock diets. Increasing the levels of those nutrients has long been a goal of plant breeders and cereal chemists. The new endosperm project uses the MGDP microarrays to track gene expression changes in corn lines with altered endosperm properties. (Larkins lab, University of Arizona: http://ag.arizona.edu/research/larkinslab/ University of Florida collaborators: http://www.napa.ufl.edu/2000news/corngene.htm)

Researchers at Iowa State University are investigating genes that cause maize seedlings to produce certain waxy compounds with potential industrial significance. Cuticular waxes protect maize plants from frost and UV radiation. They also play a role in plant-pathogen interactions and affect plant responsiveness to agricultural chemicals such as pesticides, growth regulators and foliar nutrients sprayed on plants. (Patrick Schnable, Iowa State University; http://www.pslab.agron.iastate.edu/research/cwg.shtml).

MGDP principal investigator Virginia Walbot and postdoctoral fellow Paula Casati at Stanford University are using MGDP microarrays to determine how the purple anthocyanin pigments in corn shield cells from the damaging effects of UV-B radiation. As ozone depletion occurs in the stratosphere, crops are exposed to higher levels of damaging UV-B. Just as this radiation can cause cancer in human skin by damaging the DNA and "aging" of the skin by damaging proteins, so too can it damage crops and reduce yields. Biological sunscreen pigments provide plants with a mechanism for avoiding UV-B damage.

Unlike most plants, maize has separate male (tassel) and female (ear) flowers. Identifying genes that affect the formation of the maize flower and permit selective development of pollen in the tassel and egg cells in the ear is an exciting basic research question and a fascinating story in evolution. New knowledge about flower formation in the ear could be immensely valuable for plant breeding to improve crop yields, because the number of kernels on the ear is determined by the number of flowers with eggs inside. MGD team members Sarah Hake, Bob Schmidt, and Volker Brendel have joined with collaborators in Missouri, New York, and Illinois to understand the evolution of grass flower morphology leading up to the unique specializations of maize. Using the microarrays and floral mutants from the MGDP, the maize inflorescence team seeks to discover the rules regulating maize flower formation. http://www.pgec.usda.gov/Hake/InflorescenceArchitecture.pdf

The DNA content of a maize cell is present in 20 double-stranded helices (the 20 chromosomes present in each cell). If the DNA were stretched out, it would measure nearly a meter; this is also true of human DNA content organized onto 46 chromosomes. Yet, the individual cells are only about 10 to 50 uM long. Consequently, the DNA must be highly compacted and folded to fit inside the cell; this compacted form of DNA is called chromatin. Correct packing is essential for normal gene expression and cell life. MGDP member Vicki Chandler and colleagues at the University of Arizona and other institutions are determining the number of genes and the roles of specific genes in compacting the chromatin of Arabidopsis and maize. These two plants differ by 20-fold in DNA content. http://www.chromdb.org/index.html

The Maize Gene Discovery Project sets the stage for a full-scale maize genome sequencing project. Plans for such an effort are underway, with the support of the MGDP collaborators. Researchers hope a preliminary draft sequence for maize should be available by 2005. MGDP's data will anchor the sequencing as it progresses. Rather like a difficult crossword puzzle, the parts that are known can help solve the remainder. MGDP's ESTs will help identify genes within long segments of DNA and define the intron-exon structure of genes. And the sites of RescueMu insertions . highly enriched for genes . will allow researchers to identify genes and non-genes.

When the entire maize genome has been sequenced, the true promise of maize genomics -- gaining a full understanding of corn's genetic blueprint -- will be just around the corner. In the meantime, MGDP has provided plenty of material to keep researchers busy and productive.

Katherine Miller, a freelance science writer, contributed the text for this page to the Maize Gene Discovery Project. You can reach her at [email protected].

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