Annals of Botany

Genes and beans in search of coffee quality

As I write this, I pause from time to time to take another sip from my cup of fair-traded Colombian coffee. But how much do we know about the biochemical features of the coffee bean that affect their taste or storage capacity? The answer, according to Hinniger et al. (Nestlé Research Centre, Lyon, France and Cornell University, USA, pp. 755–765) is ‘not enough’. As a result, they have undertaken a major study of the regulation of genes involved in laying down some of the major components of the developing grain. In the current paper they focus on dehydrin proteins that are expressed late in seed development. Dehydrins are a subgroup of the late embryogenesis abundant (LEA) proteins and may also be expressed elsewhere in the plant in response to water deficit. The authors have used information in the Coffea canephora EST (expressed sequence tag) database to clone cDNAs encoding three dehydrins (CcDH1, CcDH2, CcDH3) and another LEA protein (CcLEA1). Studies of the expression of the genes in C. canephora and C. arabica grains revealed slight but consistent differences between the species, but in general it can be stated that all three dehydrin genes are expressed throughout grain development and that CcDH1 and CcDH3 are also expressed in the pericarp and in other organs, including leaves and flowers. Analysis of the promoter of CcDH2 (which showed a grain-specific expression pattern) revealed ABA-response elements, dehydration-response elements and sequences related to expression during seed development. Focusing on CcLEA1, its expression in both species was confined to a very narrow ‘window’ early in grain development during the phase of perisperm shrinkage and endosperm expansion, suggesting a role for this LEA in that transition. So, while these data do not specifically answer the questions raised above, they do contribute significantly to our understanding of the developmental biology of the coffee bean.