PhD., Stanford University Medical School, 1993
Postdoctoral Research: University of Wisconsin, 1993-1997
Address: 497 Horticulture
Research InterestsFunctional Genomics of Arabidopsis Signal Transduction
Research FieldsGenomics & Proteomics
The word signal transduction is used to describe the process by which information flows through a living organism. Our laboratory is interested in understanding the basic principles underlying the process of signal transduction. The subject of our research is the model system Arabidopsis thaliana, and we are currently studying the signal transduction pathways that utilize MAP kinase cascades. MAP kinase cascades are highly-conserved signal transduction modules that are present in all eucaryotes. A MAP kinase cascade is composed of three interacting protein kinases: a MAP kinase (MAPK), a MAP kinase kinase (MAP2K), and a MAP kinase kinase kinase (MAP3K). Activation of a MAP3K by an upstream signal causes a phosphorylation cascade that ends with the activation of the MAPK. This MAPK then goes on to regulate various downstream targets such as transcription factors. Because multiple upstream signals often converge on single MAP3K, the MAPK cascade serves as an information processing unit that integrates various input signals and produces an appropriate response. The Arabidopsis genome encodes twenty-three MAPKs, ten MAP2Ks, and sixty MAP3Ks. Given the large size of these gene families, it is not surprising that MAP kinase cascades are believed to play a role in a wide variety of signal transduction pathways in Arabidopsis. The functions of most of the MAPK cascade components in Arabidopsis are unknown. One of the long-term goals of our laboratory is therefore to determine which signaling pathways are controlled by each of the MAPK cascade components found in the Arabidopsis genome. Our initial studies have focused on a group of three MAP3K genes called ANP1, ANP2, and ANP3. To determine the function of these genes, we employed a reverse-genetic strategy based on the identification of Arabidopsis plants carrying knock-out mutants for each of these genes. Using this approach, we determined that functional redundancy operates within this gene family such that single-gene mutants are all phenotypically normal, while various double-mutant combinations display obvious mutant phenotypes. Analysis of these mutant plants revealed that the process of cell division is regulated by the ANP genes. These results provided the first genetic evidence for the involvement of a MAP kinase pathway in the control of cell division in plants. Future studies in the lab will investigate how the ANP genes control cell division by exploring the upstream signals that influence the decision to initiate cytokinesis as well as the downstream targets that receive this information. In addition, we will expand our analysis of MAP kinase signaling to include other members of these large gene families. Ultimately we will investigate how plants manage cross-talk and maintain specificity between the many different MAP kinase pathways that co-exist within plant cells. In order to facilitate our analysis of signal transduction in Arabidopsis, our laboratory also works on the development of novel functional-genomic strategies. Our current work in this area is focused on methods for genome-wide mutation detection. Using custom-made oligonucleotide microarrays that contain 750,000 unique features per chip we are developing methods that should allow us to rapidly catalog the precise locations of specific mutations throughout the genome of Arabidopsis. This technology will be used to create an ordered population of mutagenized Arabidopsis lines in which any mutation of interest can be identified in a computer database and then immediately accessed as an archived seed stock. This resource will make reverse-genetic analysis extremely simple and rapid.
P.J., P.J. Jester, J.R. Gottwald, and M.R. Sussman. 2002. An
Arabidopsis MAPKK kinase gene family encodes essential positive
regulators of cytokinesis. Plant Cell 14:1109-20.
Young JC, Krysan PJ, Sussman MR. 2001. Efficient screening of Arabidopsis T-DNA insertion lines using degenerate primers. Plant Physiol. 125:513-518.
Sussman, M.R., R. Amasino, J.C. Young, P.J. Krysan, and S. Austin-Phillips. 2000. The Arabidopsis Knockout facility at the University of Wisconsin-Madison. Plant Physiol 124:1465-67.
Gottwald, J.R., P.J. Krysan, J.C. Young, R.F. Evert, and M. R. Sussman. 2000. Genetic evidence for the in planta role of phloem-specific plasma membrane sucrose transporters. Proceedings of the National Academy of Sciences USA 97:13979-84.