The 'PUCE CAFE' Project: the First 15K Coffee Microarray, a New Tool for Discovering Candidate Genes correlated to Agronomic and Quality Traits

Background: Understanding the genetic elements that contribute to key aspects of coffee biology will have an impact on future agronomical improvements for this economically important tree. During the past years, EST collections were generated in Coffee, opening the possibility to create new tools for functional genomics. Results: The "PUCE CAFE" Project, organized by the scientific consortium NESTLE/IRD/CIRAD, has developed an oligo-based microarray using 15,721 unigenes derived from published coffee EST sequences mostly obtained from different stages of fruit development and leaves in Coffea Canephora (Robusta). Hybridizations for two independent experiments served to compare global gene expression profiles in three types of tissue matter (mature beans, leaves and flowers) in C. canephora as well as in the leaves of three different coffee species (C. canephora, C. eugenoides and C. arabica). Microarray construction, statistical analyses and validation by Q-PCR analysis are presented in this study. Conclusion: We have generated the first 15 K coffee array during this PUCE CAFE project, granted by Genoplante (the French consortium for plant genomics). This new tool will help study functional genomics in a wide range of experiments on various plant tissues, such as analyzing bean maturation or resistance to pathogens or drought. Furthermore, the use of this array has proven to be valid in different coffee species (diploid or tetraploid), drastically enlarging its impact for high-throughput gene expression in the community of coffee research

Genomic expression dominance in the natural allopolyploid Coffea arabica is massively affected by growth temperature

Polyploidy occurs throughout the evolutionary history of many plants and considerably impacts species diversity, giving rise to novel phenotypes and leading to ecological diversification and colonization of new niches. Recent studies have documented dynamic changes in plant polyploid gene expression, which reflect the genomic and functional plasticity of duplicate genes and genomes. The aim of the present study was to describe genomic expression dominance between a relatively recently formed natural allopolyploid (Coffea arabica) and its ancestral parents (Coffea canephora and Coffea eugenioides) and to determine if the divergence was environment-dependent. Employing a microarray platform designed against 15 522 unigenes, we assayed unigene expression levels in the allopolyploid and its two parental diploids. For each unigene, we measured expression variations among the three species grown under two temperature conditions (26-22 degrees C (day-night temperatures) and 30-26 degrees C (day-night temperatures)). More than 35% of unigenes were differentially expressed in each comparison at both temperatures, except for C. arabica vs C. canephora in the 30-26 degrees C range, where an unexpectedly low unigene expression divergence (< 9%) was observed. Our data revealed evidence of transcription profile divergence between the allopolyploid and its parental species, greatly affected by environmental conditions, and provide clues to the plasticity phenomenon in allopolyploids

Polyploidy and its effect on evolutionary success: old questions revisited with new tools

Polyploidy, the condition of possessing more than two complete genomes in a cell, has intrigued biologists for almost a century. Polyploidy is found in many plants and some animal species and today we know that polyploidy has had a role in the evolution of all angiosperms. Despite its widespread occurrence, the direct effect of polyploidy on evolutionary success of a species is still largely unknown. Over the years many attractive hypotheses have been proposed in an attempt to assign functionality to the increased content of a duplicated genome. Among these hypotheses are the proposal that genome doubling confers distinct advantages to a polyploid and that these advantages allow polyploids to thrive in environments that pose challenges to the polyploid's diploid progenitors. This article revisits these long-standing questions and explores how the integration of recent genomic developments with ecological, physiological and evolutionary perspectives has contributed to addressing unresolved problems about the role of polyploidy. Although unsatisfactory, the current conclusion has to be that despite significant progress, there still isn't enough information to unequivocally answer many unresolved questions about cause and effect of polyploidy on evolutionary success of a species. There is, however, reason to believe that the increasingly integrative approaches discussed here should allow us in the future to make more direct connections between the effects of polyploidy on the genome and the responses this condition elicits from the organism living in its natural environment