Department of Plant Biology
Plant Sciences Building
University of Georgia
Athens, GA 30602-7271 USA
Department of Plant Biology
Plant Sciences Building
University of Georgia
Athens, GA 30602-7271 USA
The accumulation kinetics of 50 cloned cotton mRNA markers define several sequential developmental programs in embryos. These are associated with the cotyledon-stage, the concentration of endogenous abscisic acid, the maturation or reserve accumulation stage, ovule abscission, and germination/early seedling growth. Gene expression is temporally modular (combinatorial), suggesting that genes that are expressed in more than one program are regulated by program-specific factors rather than by factors that are common to several programs. Both descriptive and experimental studies indicate that ovule abscission terminates the maturation program and induces the postabscission program while imbibition induces the germination/early seedling growth program.
The structures of many of the postabscission-specific LEA proteins suggest that a major function of the embryo postabscission program, in which they are expressed, is to prepare the embryo for desiccation. Their expression is consistent with this notion; the postabscission program can be induced in immature or germinating embryos by abscisic acid, osmotic stress or desiccation. One of the approaches that we are using to address the regulation and function of these genes is to study embryo desiccation-lethal mutants in Arabidopsis. Mutant plants whose embryos die if desiccated have been recovered and maintained as homozygotes by embryo-rescue techniques. Molecular analysis of one such lethal mutant indicates that the postabscission program fails to be induced during development, suggesting that products of the postabscission program are essential for dessication tolerance.
Primary embryo dormancy is the inability of mature seed to germinate until specific environmental stimuli are perceived that predict that future conditions will support plant growth and seed set. The approach to understanding the mechanism of dormancy in Arabidopsis is to isolate mutants that germinate rapidly without the dormancy-breaking, cold stratification is this normally required. All other aspects of plant and embryo development appear normal in these mutant lines, suggesting that they are defective only in the establishment or maintenance of primary dormancy. At least 17 INSOMNIAC (NSM) genes have so far been identified. In addition to further genetic analysis, the molecular phenotypes of these mutants are being evaluated, in particular the stages in embryo development when wild-type and mutant embryos diverge, and the possible role of LEA proteins in maintaining dormancy.
Galau, G.A., K.S. Jakobsen and D.W. Hughes (1991) The controls of late dicot embryogenesis and early germination. Physiol. Plant. 81: 280-288
Hughes, D.W. and G.A. Galau (1991) Developmental and environmental induction of Lea and LeaA mRNAs and the postabscission program during embryo culture. Plant Cell 3: 605-618
Klemsdal, S.S., D. Wayne Hughes, Anders Lonneborg, Reidunn B. Aalen and Odd-Arne Olsen (1991) Primary structure of a novel barley gene differentially expressed in immature aleurone layers. Mol. Gen. Genet. 228: 9-16
Espelund, M., S. Saeboe-Larssen, D.W. Hughes, G.A. Galau, F. Larsen and K.S. Jakobsen (1992) Late embryogenesis-abundant genes encoding proteins with different numbers of hydrophilic repeats are regulated differentially by abscisic acid and osmotic stress. Plant J. 2: 241-252
Galau, G.A., H.Y.-C. Wang and D.W. Hughes (1992) Cotton Lea4 (D19) and LeaA2 (D132) Group 1 Lea genes encoding water stress-related proteins containing a 20-amino acid motif Plant Physiol. 99: 783-788
Galau, G.A., H.Y.-C. Wang and D.W. Hughes (1993) Cotton Lea5 and Lea14 encode atypical LEA proteins. Plant Physiol. 101: 695-696
Jakobsen, K.S., D.W. Hughes and G.A. Galau (1994) Simultaneous induction of postabscission and germination mRNAs in cultured dicotyledonous embryos. Planta 192: 384-394
Han, B., D.W. Hughes, G.A. Galau, J.D. Bewley and A.R. Kermode (1997) Changes in late-embryogenesis-abundant (LEA) messenger RNAs and dehydrins during maturation and premature drying of Ricinus communis L. seeds. Planta 201: 27-35
Baumbusch, L.O., I.K. Sundal, D.W. Hughes, G.A. Galau and K.S. Jakobsen (2001) Efficient protocols for CAPS-based mapping in Arabidopsis. Plant Mol. Biol. Rep. 19: 137-149
Baumbusch, L.O., D.W. Hughes, G.A. Galau and K.S. Jakobsen (2004) LEC1, FUS3, ABI3 and Em expression reveals no correlation with dormancy in Arabidopsis. J. Exp. Bot. 55: 77-87