Towards the understanding of the cocoa transcriptome: Production and analysis of an exhaustive dataset of ESTs of Theobroma cacao L. generated from various tissues and under various conditions.

BACKGROUND: Theobroma cacao L., is a tree originated from the tropical rainforest of South America. It is one of the major cash crops for many tropical countries. T. cacao is mainly produced on smallholdings, providing resources for 14 million farmers. Disease resistance and T. cacao quality improvement are two important challenges for all actors of cocoa and chocolate production. T. cacao is seriously affected by pests and fungal diseases, responsible for more than 40% yield losses and quality improvement, nutritional and organoleptic, is also important for consumers. An international collaboration was formed to develop an EST genomic resource database for cacao. RESULTS: Fifty-six cDNA libraries were constructed from different organs, different genotypes and different environmental conditions. A total of 149,650 valid EST sequences were generated corresponding to 48,594 unigenes, 12,692 contigs and 35,902 singletons. A total of 29,849 unigenes shared significant homology with public sequences from other species.Gene Ontology (GO) annotation was applied to distribute the ESTs among the main GO categories.A specific information system (ESTtik) was constructed to process, store and manage this EST collection allowing the user to query a database.To check the representativeness of our EST collection, we looked for the genes known to be involved in two different metabolic pathways extensively studied in other plant species and important for T. cacao qualities: the flavonoid and the terpene pathways. Most of the enzymes described in other crops for these two metabolic pathways were found in our EST collection.A large collection of new genetic markers was provided by this ESTs collection. CONCLUSION: This EST collection displays a good representation of the T. cacao transcriptome, suitable for analysis of biochemical pathways based on oligonucleotide microarrays derived from these ESTs. It will provide numerous genetic markers that will allow the construction of a high density gene map of T. cacao. This EST collection represents a unique and important molecular resource for T. cacao study and improvement, facilitating the discovery of candidate genes for important T. cacao trait variation.

Characterization of leafy cotyledon1-like during embryogenesis in Theobroma cacao L.

Theobroma cacao L., an economically important crop for developing countries, can be experimentally propagated by somatic embryogenesis. Because of their potential roles in embryogenesis, a gene candidate strategy was initiated to find gene homologues of the members of the leafy cotyledon family of transcription factors. A homologue of the leafy cotyledon1-like gene, that encodes the HAP 3 subunit of the CCAAT box-binding factor, was found in the cocoa genome (TcL1L). The translated peptide shared a high amino acid sequence identity with the homologous genes of Arabidopsis thaliana, Phaseolus coccineus and Helianthus annuus. TcL1L transcripts mainly accumulated in young and immature zygotic embryos, and, to a lesser extent, in young and immature somatic embryos. In situ hybridization specified the localization of the transcripts as being mainly in embryonic cells of young embryos, the meristematic cells of the shoot and root apex of immature embryos, and in the protoderm and epidermis of young and immature embryos, either zygotic or somatic. Non-embryogenic explants did not show TcL1L expression. Ectopic expression of the TcL1L gene could partially rescue the Arabidopsis lec1 mutant phenotype, suggesting a similarity of function in zygotic embryogenesis.

Pluripotent versus totipotent plant stem cells: dependence versus autonomy?

Little is known of the mechanisms that induce the dedifferentiation of a single somatic cell into a totipotent embryogenic cell that can either be regenerated or develop into an embryo and subsequently an entire plant. In this Opinion article, we examine the cellular, physiological and molecular similarities and differences between different plant stem cell types. We propose to extend the plant stem cell concept to include single embryogenic cells as a totipotent stem cell based on their capacity to regenerate or develop into an embryo under certain conditions. Our survey suggests that differences in chromatin structure might ensure that meristem-localized stem cells have supervised freedom and are pluripotent, and that embryogenic stem cells are unsupervised, autonomous and, hence, freely totipotent.