Mechanisms of plant embryo development

Vertically- and horizontally-transmitted memories - the fading boundaries between regeneration and inheritance in planaria

The Weismann barrier postulates that genetic information passes only from the germline to the soma and not in reverse, thus providing an obstacle to the inheritance of acquired traits. Certain organisms such as planaria – flatworms that can reproduce through asymmetric fission – avoid the limitations of this barrier, thus blurring the distinction between the processes of inheritance and development. In this paper, we re-evaluate canonical ideas about the interaction between developmental, genetic and evolutionary processes through the lens of planaria. Biased distribution of epigenetic effects in asymmetrically produced parts of a regenerating organism could increase variation and therefore affect the species' evolution. The maintenance and fixing of somatic experiences, encoded via stable biochemical or physiological states, may contribute to evolutionary processes in the absence of classically defined generations. We discuss different mechanisms that could induce asymmetry between the two organisms that eventually develop from the regenerating parts, including one particularly fascinating source – the potential capacity of the brain to produce long-lasting epigenetic changes.

Summary: In this hypothesis paper we re-evaluate canonical ideas about the interaction between developmental, genetic and evolutionary processes through the lens of planaria, an invertebrate model organism which challenges fundamental assumptions regarding reproduction.

TRAUCO, a Trithorax-group gene homologue, is required for early embryogenesis in Arabidopsis thaliana

Embryogenesis is a critical stage during the plant life cycle in which a unicellular zygote develops into a multicellular organism. Co-ordinated gene expression is thus necessary for proper embryo development. Polycomb and Trithorax group genes are members of evolutionarily conserved machinery that maintains the correct expression patterns of key developmental regulators by repressing and activating gene transcription. TRAUCO (TRO), a gene homologous to the Trithorax group of genes that can functionally complement a BRE2P yeast mutant, has been identified in Arabidopsis thaliana. It is demonstrated that TRO is a nuclear gene product expressed during embryogenesis, and loss of TRO function leads to impaired early embryo development. Embryos that arrested at the globular stage in the tro-1 mutant allele were fully rescued by a TRO expression clone, a demonstration that the tro-1 mutation is a true loss-of-function in TRO. Our data have established that TRO is the first trithorax-group gene homologue in plants that is required for early embryogenesis.

Computational and experimental analysis identifies Arabidopsis genes specifically expressed during early seed development

Background

Plant seeds are complex organs in which maternal tissues, embryo and endosperm, follow distinct but coordinated developmental programs. Some morphogenetic and metabolic processes are exclusively associated with seed development. The goal of this study was to explore the feasibility of incorporating the available online bioinformatics databases to discover Arabidopsis genes specifically expressed in certain organs, in our case immature seeds.

Results

A total of 11,032 EST sequences obtained from isolated immature seeds were used as the initial dataset (178 of them newly described here). A pilot study was performed using EST virtual subtraction followed by microarray data analysis, using the Genevestigator tool. These techniques led to the identification of 49 immature seed-specific genes. The findings were validated by RT-PCR analysis and in situ hybridization.

Conclusion

We conclude that the combined in silico data analysis is an effective data mining strategy for the identification of tissue-specific gene expression.