Summary Coffea arabica (Arabica) and Coffea canephora (Robusta) are the two main cultivated species used for coffee bean production. Arabica genotypes generally produce a higher coffee quality than Robusta genotypes. Understanding the genetic basis for sucrose accumulation during coffee grain maturation is an important goal because sucrose is an important coffee flavor precursor. Nine new Coffea genes encoding sucrose metabolism enzymes have been identified: sucrose phosphate synthase (CcSPS1, CcSPS2), sucrose phosphate phosphatase (CcSP1), cytoplasmic (CaInv3) and cell wall (CcInv4) invertases and four invertase inhibitors (CcInvI1, 2, 3, 4). Activities and mRNA abundance of the sucrose metabolism enzymes were compared at different developmental stages in Arabica and Robusta grains, characterized by different sucrose contents in mature grain. It is concluded that Robusta accumulates less sucrose than Arabica for two reasons: Robusta has higher sucrose synthase and acid invertase activities early in grain development – the expression of CcSS1 and CcInv2 appears to be crucial at this stage and Robusta has a lower SPS activity and low CcSPS1 expression at the final stages of grain development and hence has less capacity for sucrose re‐synthesis. Regulation of vacuolar invertase CcInv2 activity by invertase inhibitors CcInvI2 and/or CcInvI3 during Arabica grain development is considered.

There are many documented examples of viral genes retained in the genomes of multicellular organisms that may in some cases bring new beneficial functions to the receivers. The ability of certain ichneumonid parasitic wasps to produce virus-derived particles, the socalled ichnoviruses (IVs), not only results from the capture and domestication of single viral genes but of almost entire ancestral virus genome(s). Indeed, following integration into wasp chromosomal DNA, the putative and still undetermined IV ancestor(s) evolved into encoding a 'virulence gene delivery vehicle' that is now required for successful infestation of wasp hosts. Several putative viral genes, which are clustered in distinct regions of wasp genomes referred to as IVSPERs (Ichnovirus Structural Protein Encoding Regions), have been assumed to be involved in virus-derived particles morphogenesis, but this question has not been previously functionally addressed. In the present study, we have successfully combined RNA interference and transmission electron microscopy to specifically identify IVSPER genes that are responsible for the morphogenesis and trafficking of the virusderived particles in ovarian cells of the ichneumonid wasp Hyposoter didymator. We suggest that ancestral viral genes retained within the genomes of certain ichneumonid parasitoids possess conserved functions which were domesticated for the purpose of assembling viral vectors for the delivery of virulence genes to parasitized host animals. Author summaryThousands of parasitic wasp from the ichneumonid family rely on virus-derived particles, named Ichnoviruses (Polydnavirus family), to ensure their successful development. The particles are produced in a specialized ovarian tissue of the female wasp named calyx. Virions are assembled in the calyx cell nuclei and stored in the oviduct before being transferred to the parasitoid host upon female wasp oviposition. Genes encoding proteins PLOS Pathogens | https://doi.

No abstract