Projects
Last changed: 14 December 2021
Embryogenesis and Phase Change
Plants undergo several developmental transitions during their life cycle. Germination is the transition between embryonic and post-embryonic development. After germination, the seedling passes through the juvenile vegetative growth phase, where it is not competent to flower. The third major transition is the floral transition from the adult vegetative phase to the reproductive phase. Embryology Most morphogenic events in plants occur in the sporophyte following seed germination, however, the embryonic phase is crucial as it is then the meristems and the shoot-root plant body pattern are specified. Mutagenesis and the subsequent screening for and analysis of mutants, mainly in Arabidopsis, has been elucidating the genetic regulation of embryonic pattern formation in Angiosperms. In contrast, hardly anything is known about embryo development in gymnosperms. Gymnosperms have several disadvantages as experimental organisms. They have large genomes, about 200 to 400 times bigger than in Arabidopsis, larger size and a long regeneration time. Molecular data suggest that extant seed plants (gymnosperms and angiosperms) share a last common ancestor about 285 million years ago. Therefore, characterization of the genes regulating embryo development, their expression pattern and their functions in gymnosperm is interesting from an evolutionary point of view. But it is also important for increasing the possibilities to propagate the economically important conifers via somatic embryos. We have developed somatic embryogenesis in Norway spruce as a model system for studying embryology in conifers. The somatic embryo system in Norway spruce includes a stereotyped sequence of developomental stages, resembling zygotic embryogeny, which can be synchronized by specific treatments, making it possible to collect a large number of somatic embryos at specific developmental stages. We are analysing changes in global gene expression during differentiation of somatic embryos in Norway spruce and Scots pine in order to identify genes and processes which regulate embryo development. Expression patterns and functions of identified candidate genes are analysed. Phase Changes Plant development requires the precise temporal and spatial expression of regulatory genes, which is partly mediated by epigenetic mechanisms. We are studying how epigenetic changes regulate the transition form the embryonic to the post-embryonic phase. The duration of the juvenile vegetative growth phase in Norway spruce and Scots pine is 20-25 and 8-20 years, respectively. A research priority is to shorten this time, which will enable more cycles of selection per unit time and faster progress in forest tree breeding. The genes involved in the transition from the adult vegetative phase to the reproductive phase are becoming better known in Arabidopsis. However, very little is known about the regulation of the transition between different developmental phases in conifers. We are analysing changes in gene expression during the transition from the adult vegetative phase to the reproductive phase in Norway spruce and Scots pine. In addition to providing insight as to how the regulation of phase changes has evolved, changes in gene activity are potentially useful to indicate passage through the juvenile phase (how close a tree is to flowering). Such knowledge is crucial for attempts to stimulate flowering in seed orchards.
Zhu, T., Moschou, P. N., Alvarez J.M., Sohlberg, J. and Von Arnold, S. 2014. WUSCHEL-RELATED HOMEOBOX 8/9 is important for proper embryo patterning in the gymnosperm Norway spruce. Journal of Experimental Botany 65:6543-6552. Hedman, H., Zhu, T., von Arnold, S. and Sohlberg, J. 2013. Analysis of the WUSCHEL-RELATED HOMEOBOX gene family in the conifer Picea abies reveals extensive conservation as well as dynamic patterns. BMC Plant Biology 13:89. Uddenberg, D., Reimgård, J., Clapham, D., Almqvist, C., von Arnold, S., Emanuelsson, O. and Sundström, J. 2013. Early cone-setting in Picea abies var. acrocona is associated with increased transcriptional activity of MADS-box transcription factor. Plant Physiol 161:813-823. Larsson, E., Sundström, J., Sitbon, F. and von Arnold, S. 2012. Expression of PaNAC01, a Picea abies CUP-SHAPED COTYLEDON orthologue, is regulated by polar auxin transport and associated with differentiation of the shoot apical meristem and formation of separated cotyledons. Annals of Botany 110:923-934. Vestman, D., Larsson, E., Uddenberg, D., Cairney, J., Clapham, D. and von Arnold, S. 2010. Important processes during differentiation and early development of somatic embryos of Norway spruce as revealed by changes in global gene expression. Tree Genetic and Genomes 7:347-352 Larsson, E., Sitborn, F., Ljung, K. and von Arnold, S. 2008. Inhibited polar auxin transport results in aberrant embryo development in Norway spruce. New Phytol. 177:356-366. Helmersson, A., von Arnold, S. and Bozhkov, P. 2008. The level of free intracellular zink mediates programmed cell death/cell survival decisions in plant embryos. Plant Physiology 147:1158-1167. |