Sarah Hake, University of California, Berkeley, P.I. David Jackson, Cold Spring Harbor, Co-P.I. Elizabeth Kellogg, University of Missouri, St. Louis, Co-P.I. Torbert Rocheford, University of Illinois, Champaign, Co-P.I. Robert Schmidt, University of California, San Diego, Co-P.I. Erik Vollbrecht, Iowa State University, Co-P.I. Volker Brendel, Iowa State University, Senior Personnel Richard Johnson, University of Illinois, Cooperator

The overall goals of this project is to uncover the network of genetic interactions responsible for maize inflorescence development. A longterm goal is to understand the genetic basis for diversification in inflorescence morphology in grasses, a group of about 10,000 plant species including major cereal crops. The inflorescence is a flowering structure and hold seeds (grains in case of cereals). The variation in architecture of plant inflorescences is largely determined by the activity of meristems, small groups of stem cells that perpetuate themselves and give rise to organs. The diversity among grass inflorescences is particularly striking and results from variation in the identity and determinacy of several distinct meristems produced throughout inflorescence development. This diversity has important agricultural implications as pollen and seeds are produced on branches of the inflorescence. In their previous grant, the investigators cloned a number of key genes that regulate critical steps in the pathway of inflorescence development, from meristem initiation and organization to patterns of branching and meristem determinacy. The specific objective of the current project is to determine how these genes fit into a larger genetic network and to determine divergence and conservation of networks in maize and other grasses. The project takes advantage of new high resolution maize mapping resources and the expected genome sequence to fine map quantitative trait loci (QTL) and use association analysis to link genotype with phenotype.

The research will address questions such as why the maize ear and tassel are so distinct yet arise from similar primordia, what are the genes that differentiate diverse branching structures of the grasses, and how variation in inflorescence architecture genes regulates the diverse architectures of maize inbred lines. Answers to these questions will establish a foundation for genetic studies of reproductive biology in cereals and other grass species. In this project, key genes and gene networks that integrate the early steps in ear and tassel development will be identified and those that underlie their distinct phenotypes will be uncovered. These will serve as tools for research in developmental biology, evolutionary biology, applied genetics and breeding, with obvious relevance to maize hybrid seed production and crop improvement. The summer outreach program aims to reach a large number of high school students and undergraduates and provide hands-on experience in field and laboratory genetics and genomics.

Access to project outcomes The mutants to be identified will be in defined inbred backgrounds and will be made available through the Maize Genetics Stock Center ( Project data will be made available through MaizeGDB (

Project Report

The food supply is largely determined by the grains of cereal crops such as maize, rice, and wheat. The grains are born from inflorescences, groups of flowers arranged along branches. Our research was carried out on the the inflorescences of maize, which are the ear and tassel. At the inception of development, ear and tassel primordia are very similar with the exception of the branch primordia in the tassel. As development proceeds, specialization occurs in each inflorescence, leading to female flowers in the ear, the kernels, and male flowers in the tassel, the anthers. Genes were identified that regulate aspects of inflorescence development such as number of rows of kernels, number of tassel branches, and sex determination. Investigations into other grasses showed that some of the genes we identified were conserved across all grasses, whereas others were unique to certain groups of grasses. We determined the connections between different genes by comparing the expression patterns of different mutants. This data revealed a core of a few hundred genes that are specifically expressed in ear and tassel primordia and are modulated by the mutations that affect branching. We also determined the connections between genes by asking which genes are regulated by key transcription factors. To identify additional genes that regulate the inflorescence, we took advantage of the natural diversity of maize using a quantitative trait approach. The results suggest that additional genes affecting the infloresence may be discovered by identifying the genes behind quantitative traits. At the end of the day, knowledge of the genes and networks identified can be used to breed for increased grain production in multiple cereal species.

National Science Foundation (NSF)
Division of Integrative Organismal Systems (IOS)
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Diane Jofuku Okamuro
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University of California Berkeley
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