Biogenesis of flavor-related linalool is diverged and genetically conserved in tree peony (Paeonia × suffruticosa)

High-quality assembly and methylome of a Tibetan wild tree peony genome (Paeonia ludlowii) reveal the evolution of giant genome architecture

Tree peony belongs to one of the Saxifragales families, Paeoniaceae. It is one of the most famous ornamental plants, and is also a promising woody oil plant. Although two Paeoniaceae genomes have been released, their assembly qualities are still to be improved. Additionally, more genomes from wild peonies are needed to accelerate genomic-assisted breeding. Here we assemble a high-quality and chromosome-scale 10.3-Gb genome of a wild Tibetan tree peony, Paeonia ludlowii, which features substantial sequence divergence, including around 75% specific sequences and gene-level differentials compared with other peony genomes. Our phylogenetic analyses suggest that Saxifragales and Vitales are sister taxa and, together with rosids, they are the sister taxon to asterids. The P. ludlowii genome is characterized by frequent chromosome reductions, centromere rearrangements, broadly distributed heterochromatin, and recent continuous bursts of transposable element (TE) movement in peony, although it lacks recent whole-genome duplication. These recent TE bursts appeared during the uplift and glacial period of the Qinghai-Tibet Plateau, perhaps contributing to adaptation to rapid climate changes. Further integrated analyses with methylome data revealed that genome expansion in peony might be dynamically affected by complex interactions among TE proliferation, TE removal, and DNA methylation silencing. Such interactions also impact numerous recently duplicated genes, particularly those related to oil biosynthesis and flower traits. This genome resource will not only provide the genomic basis for tree peony breeding but also shed light on the study of the evolution of huge genome structures as well as their protein-coding genes.

Identification of Floral Volatile Components and Expression Analysis of Controlling Gene in Paeonia ostii 'Fengdan' under Different Cultivation Conditions

In order to explore the release rule of floral volatile substances and the diurnal variation of different flower development stages of Paeonia ostii 'Fengdan' in potted and ground-planted conditions, dynamic headspace adsorption combined with gas chromatography-mass spectrometry(GC-MS) was used to analyze the dynamic changes in floral volatile components and contents. Quantitative real-time PCR (qRT-PCR) was used to analyze changes in flower fragrance-regulating genes PsPAL, PsTPSs, and PsbHLH at different flower development stages and a daily change process at the full-blooming stage. The results show that there were differences in aroma components and contents of Paeonia ostii 'Fengdan' at different flower development stages and different time quantum of every day. There were 25 and 28 aroma components identified in 7 flower development stages of tree peonies planted in pots and in the field, respectively, and 23 and 22 aroma components identified at different time quantum of the day, of which the largest and highest content was alkanes. The main characteristic aroma substances were (E)-β-ocimene, 1,3,5-trimethoxybenzene, 2,4-di-tert-butylphenol, methyl jasmonate, nerol, and cinnamyl alcohol; released amounts of the abovementioned substances varied depending on the development stage and the time of the day. The expression of flower fragrance-controlling genes (PsPAL, PsTPSs, and PsbHLH) in tree peonies varied greatly in different conditions. The results of this study provide a valuable resource to investigate floral fragrance formation in tree peonies.