Progress 09/01/01 to 09/01/03
Outputs
This award has resulted in the isolation of two repressor genes of AGAMOUS namely SEUSS and BELLRINGER using the map-based cloning approach (Franks et al., 2002; Bao et al., 2004). Further, the award has allowed us to further pursue biochemical characterizations of LEUNIG and SEUSS (Sridhar et al., 2004; 2006). These studies were published in four research articles listed below.
Impacts
The research provides important mechanistic insights into how repressor genes function in plants. Such knowledge will be useful for future genetic engineering aimed at specifically switching on or off genes in order to improve crop traits. The result also illustrates how plant reproductive organs develop according to the activities of one or a few key regulatory genes. This will enable future genetic manipulation of reproductive organ formation. Since most fruits, nuts, and vegetables (such as tomato, squash) develop from the pistil of a flower, the ability to regulate the spatial and temporal activities of the class C gene may enable one to increase fruit number and size. Further, as pistils are bearers of seeds, the ability to regulate pistil development may enhance grain yield and seed production. In addition, the class C gene may serve as the target for gene repression and gene silencing leading to sterile flowers ideally suited for preventing transgene flow in the
wild. Finally, regulatory sequences that normally direct the expression of the class C gene may be used to drive the expression of foreign genes such as vaccines in fruits, leading to value-added new crops.
Publications
- 1. Franks, R. Wang, C., Levin, J. Z., and Liu, Z. (2002) SEUSS, a member of a novel family of plant regulatory proteins, represses floral homeotic gene expression with LEUNIG. Development 129: 253-263 (COVER)
- 2. X. Bao, Franks, R.G., Levin, J.Z., and Liu, Z. (2004) Repression of AGAMOUS by BELLRINGR, in Floral and Inflorescence Meristems. Plant Cell 16, 1478-1489.
- 3. Vaniyambadi .V. Sridhar, Anandkumar Surendrarao, Deyarina Gonzalez, S. Conlan, Z. Liu (2004). Transcriptional repression of target genes by LEUNIG and SEUSS, two interacting regulatory proteins for Arabidopsis flower development. Proc Natl Acad Sci U S A. 101, 11494-11499.
- 4. Vaniyambadi .V. Sridhar, Anandkumar Surendrarao, and Z. Liu (2006). APETALA1 and SEPALLATA3 interact with SEUSS to mediate transcription repression during flower development. Development 133, 3159-3166
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Progress 01/01/01 to 12/31/01
Outputs
Flowers are the reproductive organs of higher plants. The majority of our daily food and feed come from flowers or products of flowers. Our goals are to identify key regulatory genes and reveal the molecular mechanisms underlying how a flower is made. We are focused on studying the regulatory mechanism for floral homeotic gene expression, because proper regulation of floral homeotic gene expression is critical for floral organ development. Specifically, a negative regulatory mechanism ensures that the floral homeotic gene AGAMOUS mRNA is only expressed in the center of an Arabidopsis floral meristem in order to specify stamen and carpel identity and to repress further proliferation of the floral meristem. We have identified a novel gene, SEUSS, that is required in the negative regulation of AGAMOUS. Mutations in SEUSS cause ectopic and precocious expression of AGAMOUS mRNA, leading to partial homeotic transformation of floral organs in the outer two whorls. The
effects of seuss mutations are most striking when combined with mutations in LEUNIG, a previously identified repressor of AGAMOUS. More complete homeotic transformation of floral organs and a greater extent of organ loss in all floral whorls were observed in the seuss leunig double mutants. Since the beginning of year 2001, we performed in situ hybridization to examine AGAMOUS expression in leunig seuss double mutants and observed an enhanced ectopic AGAMOUS expression in outer whorls of a flower. We constructed the agamous leunig seuss triple mutants and showed that the enhanced floral homeotic transformation and organ loss phenotype was suppressed in the triple mutants. Thus, the enhanced defect of leunig seuss double mutants was caused by an enhanced ectopic and precocious expression of AGAMOUS. Using a map-based approach, we isolated the SEUSS gene and showed that it encodes a novel protein with at least two glutamine-rich domains and a highly conserved domain that shares sequence
identity with the dimerization domain of the LIM-Domain-Binding transcription co-regulators in animals. Further, using the yeast two-hybrid assay, we found that SEUSS and LEUNIG proteins physically interact with each other, suggesting that both genes may encode components of a transcriptional co-repressor complex. The LEUNIG/SEUSS complex maybe recruited by other DNA-binding transcription factors to the AGAMOUS cis-regulatory sequence to repress AGAMOUS transcription.
Impacts
The identification and the molecular cloning of the SEUSS gene as well as the understanding of the repression mechanism for floral homeotic gene expression will have important practical applications in the control of plant fertility. Due to the conservation of the genetic mechanisms between Arabidopsis and other flowering plants, our work will advance efforts to manage agricultural productivity and reproductive competence in commercially important varieties. Therefore, our research is vitally important to the agriculture and rural life of our state.
Publications
- Franks, R. Wang, C., Levin, J. Z., and Liu, Z. (2002) SEUSS, a member of a novel family of plant regulatory proteins, represses floral homeotic gene expression with LEUNIG. Development 129: 253-263 (COVER).
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