OPENRosaceae is the most important fruit-producing clade, and its key commercially relevant genera (Fragaria, Rosa, Rubus and Prunus) show broadly diverse growth habits, fruit types and compact diploid genomes. Peach, a diploid Prunus species, is one of the best genetically characterized deciduous trees. Here we describe the high-quality genome sequence of peach obtained from a completely homozygous genotype. We obtained a complete chromosome-scale assembly using Sanger whole-genome shotgun methods. We predicted 27,852 protein-coding genes, as well as noncoding RNAs. We investigated the path of peach domestication through whole-genome resequencing of 14 Prunus accessions. The analyses suggest major genetic bottlenecks that have substantially shaped peach genome diversity. Furthermore, comparative analyses showed that peach has not undergone recent whole-genome duplication, and even though the ancestral triplicated blocks in peach are fragmentary compared to those in grape, all seven paleosets of paralogs from the putative paleoancestor are detectable.

Peach flesh color (white or yellow) is among the most popular commercial criteria for peach classification, and has implications for consumer acceptance and fruit nutritional quality. Despite the increasing interest in improving cultivars of both flesh types, little is known about the genetic basis for the carotenoid content diversity in peach. Here we describe the association between genotypes at a locus encoding the carotenoid cleavage dioxygenase 4 (PpCCD4), localized in pseudomolecule 1 of the Prunus persica reference genome sequence, and the flesh color for 37 peach varieties, including two somatic revertants, and three ancestral relatives of peach, providing definitive evidence that this locus is responsible for flesh color phenotype. We show that yellow peach alleles have arisen from various ancestral haplotypes by at least three independent mutational events involving nucleotide substitutions, small insertions and transposable element insertions, and that these mutations, despite being located within the transcribed portion of the gene, also result in marked differences in transcript levels, presumably as a consequence of differential transcript stability involving nonsense-mediated mRNA decay. The PpCCD4 gene provides a unique example of a gene for which humans, in their quest to diversify phenotypic appearance and qualitative characteristics of a fruit, have been able to select and exploit multiple mutations resulting from a variety of mechanisms.

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Several complex physiological processes, which include long-distance translocation in the phloem and unloading in sink tissues, govern the partitioning of sugars in economically important organs, such as peach fruit. In this study, we took advantage of a symplastic tracer, carboxyfluorescein (CF), providing evidence for an apoplastic sucrose transfer in the early (SI) and middle (SIII) phases of peach fruit development. Moreover, using a combination of in situ hybridization and laser microdissection-assisted expression analysis, three putative sucrose transporters encoding genes (PpSUT1, PpSUT2, PpSUT4) were transcriptionally analyzed to relate their expression with sucrose storage in this organ. Our study revealed that PpSUT2 and PpSUT4 are the genes predominantly expressed in fruit flesh, and the detailed analysis of their expression pattern in the different cell types enabled us to suggest a specialized role in sucrose distribution. Both PpSUTs transporters could be involved in the retrieval of sucrose lost from the symplastic continuum of the phloem and, when expressed in parenchyma cells, they could be active in the import of sucrose into sink tissues, via symport from the apoplast. An alternative hypothesis has been proposed and discussed for PpSUT4 because of its putative tonoplastic localization. Taken together, our results provide new insights into the molecular mechanisms underpinning sucrose unloading and accumulation in peach fruit.

The role of wind and bees in kiwifruit (Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson) pollination was investigated using large cages enclosing 80 mature vines and assembled so as to prevent insects entering without reducing wind flow within the cages. Monitoring wind speed within the cage and in the open orchard showed that the cages were suitable for such experimentation. Cages without hives, cages with hives, open pollination with hives, and hand pollination were compared during 1990 and 1991. Wind pollination led to an appreciable fruit set (81 and 98% in the first and second year respectively) but fruit weight was low, averaging 61 and 66 g. The use of hives resulted in 98-100% fruit set, but fruit size did not improve significantly, remaining far below that achieved by hand pollination (66 g versus 108 g, the first year; 78 g versus 119 g, the second year). The short flowering period, the frequent adverse weather conditions, and the unpredictable foraging efficiency of bee colonies, made both wind and honey bees inadequate for kiwifruit pollination. Only hand pollination guaranteed maximal fruit size in each year.