 |
 |
|
|
 |
|
|
We are studying the molecular basis of the initiation and patterning of lateral organs in plants, using maize as a model system. Lateral organs of the adult plant, such as leaves, develop from a group of stem cells called the meristem. A family of homeobox genes--knotted 1 (kn1) and others--is expressed in the shoot apical meristem and is required to maintain the tissue.
A section through a maize shoot apex showing the expresion pattern of knotted 1 (kn1) mRNA. kn1 is expressed in the shoot apical meristem and is downregulated at the sites of leaf initiation.
|
In normal maize, these homeobox genes are not expressed in lateral organs. However, maize that carry a mutant form of the rough sheath2 (rs2) gene express the kn1 family of genes in sectors of the leaf. We have cloned the normal rs2 gene, which encodes a MYB domain protein that is required for repressing the expression of the kn1 gene family. We are currently analyzing the mode of action of rs2; preliminary data suggest that it may act as an epigenetic regulator, possibly by changing the organization of chromatin. We are also trying to identify other genes that affect leaf initiation or that interact with rs2.
Following initiation of the lateral organ, its developmental axes are specified, which ultimately results in the differentiation of specific cell types in the appropriate positions. We are using transposable elements to generate mutants that affect axis specification and other early patterning events, and have identified a mutant, leafbladeless1 (lbl1), which affects dorsoventral patterning. We are in the process of cloning the lbl1 gene.
These studies will add to our understanding of the genetic factors that contribute to the diversity of leaf shapes among many plant species and may result in the improvement of crop species, e.g., by generating shade-tolerant varieties.
Selected Publications
Timmermans, M.C.P., Schultes, N.P., Janovsky, J.P., and Nelson, T. 1998. Leafbladeless1 is required for dorsoventrality of lateral organs in maize. Development 125: 2813-2823.
Timmermans, M.C.P., Hudson, A., Becraft, P.W., and Nelson, T. 1999. ROUGH SHEATH2: A Myb Protein That Represses knox Homeobox Genes in Maize Lateral Organ Primordia. Science 284: 151-153.
|
|
|
|
|
|
