Pomegranate (Punica granatum L.) is a perennial fruit crop grown since ancient times that has been planted worldwide and is known for its functional metabolites, particularly punicalagins. We have sequenced and assembled the pomegranate genome with 328 Mb anchored into nine pseudo-chromosomes and annotated 29 229 gene models. A Myrtales lineage-specific whole-genome duplication event was detected that occurred in the common ancestor before the divergence of pomegranate and Eucalyptus. Repetitive sequences accounted for 46.1% of the assembled genome. We found that the integument development gene INNER NO OUTER (INO) was under positive selection and potentially contributed to the development of the fleshy outer layer of the seed coat, an edible part of pomegranate fruit. The genes encoding the enzymes for synthesis and degradation of lignin, hemicelluloses and cellulose were also differentially expressed between soft- and hard-seeded varieties, reflecting differences in their accumulation in cultivars differing in seed hardness. Candidate genes for punicalagin biosynthesis were identified and their expression patterns indicated that gallic acid synthesis in tissues could follow different biochemical pathways. The genome sequence of pomegranate provides a valuable resource for the dissection of many biological and biochemical traits and also provides important insights for the acceleration of breeding. Elucidation of the biochemical pathway(s) involved in punicalagin biosynthesis could assist breeding efforts to increase production of this bioactive compound.

The expanded outer seed coat and the rigid inner seed coat of pomegranate seeds, both affect the sensory qualities of the fruit and its acceptability to consumers. Pomegranate seeds are also an appealing model for the study of seed coat differentiation and development. We conducted nontarget metabolic profiling to detect metabolites that contribute to the morphological differentiation of the seed coats along with transcriptomic profiling to unravel the genetic mechanisms underlying this process. Comparisons of metabolites in the lignin biosynthetic pathway accumulating in seed coat layers at different developmental stages revealed that monolignols, including coniferyl alcohol and sinapyl alcohol, greatly accumulated in inner seed coats and monolignol glucosides greatly accumulated in outer seed coats. Strong expression of genes involved in monolignol biosynthesis and transport might explain the spatial patterns of biosynthesis and accumulation of these metabolites. Hemicellulose constituents and flavonoids in particular accumulated in the inner seed coat, and candidate genes that might be involved in their accumulation were also identified. Genes encoding transcription factors regulating monolignol, cellulose, and hemicellulose metabolism were chosen by coexpression analysis. These results provide insights into metabolic factors influencing seed coat differentiation and a reference for studying seed coat developmental biology and pomegranate genetic improvement.

The TIFY family is a plant-specific gene family involved in regulating many plant processes, such as development and growth, defense and stress responses, fertility and reproduction, and the biosynthesis of secondary metabolites. The v2.0 peach (Prunus persica) genome, which has an improved chromosome-scale assembly and contiguity, has recently been released, but a genome-wide investigation of the peach TIFY family is lacking. In this study, 16 TIFY family genes from the peach genome were identified according to the peach reference genome sequence information and further validated by cloning sequencing. The synteny, phylogenetics, location, structure, and conserved domains and motifs of these genes were analyzed, and finally, the peach TIFY family was characterized into 9 JAZ, 1 TIFY, 1 PPD and 5 ZML subfamily members. Expression profiles of peach JAZ, PPD, and ZML genes in various organs and fruit developmental stages were analyzed, and they showed limited effects with fruit ripening cues. Four TIFY members were significantly affected at the mRNA level by exogenous treatment with MeJA in the peach epicarp, and among them, PpJAZ1, PpJAZ4 and PpJAZ5 were significantly correlated with fruit epicarp pigmentation. In addition, the TIFY family member protein interaction networks established by the yeast two-hybrid (Y2H) assay not only showed similar JAZ-MYC2 and JAZ homo- and heterodimer patterns as those found in Arabidopsis but also extended the JAZ dimer network to ZML-ZML and JAZ-ZML interactions. The PpJAZ3-PpZML4 interaction found in this study suggests the potential formation of the ZML-JAZ-MYC complex in the JA-signaling pathway, which may extend our knowledge of this gene family’s functions in diverse biological processes.

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