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RESEARCH INTERESTS
Molecular genetics of plant development
Female gametophyte development and function
Endosperm development and funtion
PUBLICATIONS
Our lab studies the molecular genetics of seed development. Our current focus is on development of the female gametophyte and endosperm. The female gametophyte is a seven-celled haploid structure that develops within the ovule of the carpel. The female gametophyte is essential for seed development because it contains the egg cell and central cell, which become fertilized and give rise to the seed's embryo and endosperm, respectively. Endosperm is an important component of the seed because it provides nutrients and developmental signals to the embryo during seed development. Furthermore, endosperm is an important source of food, feed, and industrial raw materials. Approximately two-thirds of human calories are derived from endosperm. Endosperm is used as a raw material for numerous industrial products including ethanol.
Our goal is to understand the molecular processes controlling endosperm and female gametophyte development. We are taking three complementary approaches: forward genetics, reverse genetics, and genomics. For these studies, we are using the model genetic organism Arabidopsis thaliana.
In forward-genetics screens, we identified a large collection of mutants affected in female gametophyte and endosperm development (Christensen et al., 2002; Yadegari and Drews, 2004). Further analysis of these mutants led to the identification of genes required for nuclear fusion (Portereiko et al., 2006b) and cell death (Christensen et al., 2002) during female gametophyte development.
The forward-genetics approach also led to the identification of several type I MADS domain transcription factors important for endosperm development. Two of these are AGL80 and AGL62. AGL80 is expressed in the central cell and regulates the expression of genes necessary for central cell and early endosperm development (Portereiko et al., 2006a). AGL62 regulates cellularization during early endosperm development (Kang et al., 2008). A current focus in the lab is analysis of additional type I MADS box genes regulating endosperm development.
Using genomics approaches, we identified a large collection of genes expressed in specific cells of the female gametophyte and endosperm (Steffen et al., 2007). Many of the identified genes encode transcription factors and we currently are using the reverse-genetics resources available for Arabidopsis to determine the functions of these genes. One of these genes is MYB98, which encodes a MYB transcription factor and is expressed in the synergid cells (Kasahara et al., 2005). MYB98 regulates the expression of a large set of genes (>50 genes) required for pollen tube guidance and filiform apparatus formation, which are two unique features of the synergid cells (Punwani et al., 2007). Most of the downstream genes encode cysteine-rich peptides (CRPs) that localize to the filiform apparatus, suggesting that they play a role in the formation or function (e.g., pollen tube guidance) of this structure (Punwani et al., 2007). We currently are analyzing MYB98 regulation of the downstream genes and are using the Arabidopsis reverse-genetics resources and RNAi approaches to determine the functions of the CRP genes. Similar approaches are being used to analyze the functions of the other transcription factor genes.
Selected Publications
Kang, I-H., Steffen, J.G., Portereiko, M.F., Lloyd, A., and Drews, G.N. (2008) The AGL62 MADS domain protein regulates cellularization during endosperm development in Arabidopsis. Plant Cell, in press.
Punwani, J.A., and Drews, G.N. (2008) Development and function of the synergid cell. Sexual Plant Reproduction 21, 7-15.
Punwani, J.A., Rabiger, D.S., and Drews, G.N. (2007) MYB98 positively regulates a battery of synergid-expressed genes encoding filiform apparatus-localized proteins. Plant Cell 19, 2557-2568.
Steffen, J.G., Kang, I-H., Macfarlane, J., and Drews, G.N. (2007) Identification of genes expressed in the Arabidopsis female gametophyte. Plant Journal 51, 281-292.
Sandaklie-Nikolova, L., Palanivelu, R., King, E.J., Copenhaver, G.P., and Drews, G.N. (2007) Synergid cell death in Arabidopsis is triggered following direct interaction with the pollen tube. Plant Physiology 144, 1753-1762.
Coury, D. A., Ko, A., Skaggs, M. I., Christensen, C. A., Christensen, Drews, G. N., Feldmann, K. A., and Yadegari, R. (2007) Segregation distortion in Arabidopsis gametophytic factor 1 (gfa1) mutants is caused by a deficiency of an essential RNA splicing factor. Sexual Plant Reproduction 20, 87-89.
Portereiko, M.F., Lloyd, A., Steffen, J.G., Punwani, J.A., Otsuga, D., and Drews, G.N. (2006a) AGL80 is required for central cell and endosperm development in Arabidopsis. Plant Cell 18, 1862-1872.
Portereiko, M.F., Sandaklie-Nikolova, Lloyd, A., Dever, C., Otsuga, D., and Drews, G.N. (2006b) NUCLEAR FUSION DEFECTIVE1 is required for karyogamy during fertilization and encodes the Arabidopsis RPL21M protein. Plant Physiology 141, 957-965.
Kasahara, R.D., Portereiko, M.F., Sandaklie-Nikolova, L., Rabiger, D.S., Drews, G.N. (2005) MYB98 is required for pollen tube guidance and synergid cell differentiation in Arabidopsis. Plant Cell 17, 2981-2992.
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