Tree peony transcription factor PrWRI1 enhances seed oil accumulation

BACKGROUND

WRINKLED1 (WRI1) encodes a transcription factor, belonging to the APETALA2 (AP2) family, and plays a key role in regulating plant oil biosynthesis. As a newly woody oil crop, tree peony (Paeonia rockii) was notable for the abundant unsaturated fatty acids in its seed oil. However, the role of WRI1 during the accumulation of P. rockii seeds oil remains largely unknown.

RESULTS

In this study, a new member of the WRI1 family was isolated from P. rockii and was named PrWRI1. The ORF of PrWRI1 consisted of 1269 nucleotides, encoding a putative protein of 422 amino acids, and was highly expressed in immature seeds. Subcellular localization analysis in onion inner epidermal cells showed that PrWRI1 was located at the nucleolus. Ectopic overexpression of PrWRI1 could significantly increase the total fatty acid content in Nicotiana benthamiana leaf tissue and even PUFAs in transgenic Arabidopsis thaliana seeds. Furthermore, the transcript levels of most genes related to fatty acids (FA) synthesis and triacylglycerol (TAG) assembly were also up-regulated in transgenic Arabidopsis seeds.

CONCLUSIONS

Together, PrWRI1 could push carbon flow to FA biosynthesis and further enhance the TAG amount in seeds with a high proportion of PUFAs.

Diacylglycerol Acyltransferase 3(DGAT3) Is Responsible for the Biosynthesis of Unsaturated Fatty Acids in Vegetative Organs of Paeonia rockii

'Diacylglycerol acyltransferase (DGAT)' acts as a key rate-limiting enzyme that catalyzes the final step of the de novo biosynthesis of triacylglycerol (TAG). The study was to characterize the function of the DGAT3 gene in Paeonia rockii, which is known for its accumulation of high levels of unsaturated fatty acids (UFAs). We identified a DGAT3 gene which encodes a soluble protein that is located within the chloroplasts of P. rockii. Functional complementarity experiments in yeast demonstrated that PrDGAT3 restored TAG synthesis. Linoleic acid (LA, C18:2) and α-linolenic acid (ALA, C18:3) are essential unsaturated fatty acids that cannot be synthesized by the human body. Through the yeast lipotoxicity test, we found that the yeast cell density was largely increased by adding exogenous LA and, especially, ALA to the yeast medium. Further ectopic transient overexpression in Nicotiana benthamiana leaf tissue and stable overexpression in Arabidopsis thaliana indicated that PrDGAT3 significantly enhanced the accumulation of the TAG and UFAs. In contrast, we observed a significant decrease in the total fatty acid content and in several major fatty acids in PrDGAT3-silenced tree peony leaves. Overall, PrDGAT3 is important in catalyzing TAG synthesis, with a substrate preference for UFAs, especially LA and ALA. These results suggest that PrDGAT3 may have practical applications in improving plant lipid nutrition and increasing oil production in plants.

PrMYB5 activates anthocyanin biosynthetic PrDFR to promote the distinct pigmentation pattern in the petal of Paeonia rockii

Paeonia rockii is well-known for its distinctive large dark-purple spot at the white petal base and has been considered to be the main genetic source of spotted tree peony cultivars. In this study, the petal base and petal background of Paeonia ostii (pure white petals without any spot), P. rockii, and other three tree peony cultivars were sampled at four blooming stages from the small bell-like bud stage to the initial blooming stage. There is a distinct difference between the pigmentation processes of spots and petal backgrounds; the spot pigmentation was about 10 days earlier than the petal background. Moreover, the cyanin and peonidin type anthocyanin accumulation at the petal base mainly contributed to the petal spot formation. Then, we identified a C1 subgroup R2R3-MYB transcription factor, PrMYB5, predominantly transcribing at the petal base. This is extremely consistent with PrDFR and PrANS expression, the contents of anthocyanins, and spot formation. Furthermore, PrMYB5 could bind to and activate the promoter of PrDFR in yeast one-hybrid and dual-luciferase assays, which was further verified in overexpression of PrMYB5 in tobacco and PrMYB5-silenced petals of P. rockii by comparing the color change, anthocyanin contents, and gene expression. In summary, these results shed light on the mechanism of petal spot formation in P. rockii and speed up the molecular breeding process of tree peony cultivars with novel spot pigmentation patterns.

Association mapping for yield traits in Paeonia rockii based on SSR markers within transcription factors of comparative transcriptome

BACKGROUND

Allelic variation underlying the quantitative traits in plants is caused by the extremely complex regulation process. Tree peony originated in China is a peculiar ornamental, medicinal and oil woody plant. Paeonia rockii, one of tree peony species, is a precious emerging woody oil crop. However, in this valuable plant, the study of functional loci associated with yield traits has rarely been identified. Therefore, to explore the genetic architecture of 24 yield quantitative traits, the association mapping was first reported in 420 unrelated cultivated P. rockii individuals based on the next-generation sequencing (NGS) and single-molecule long-read sequencing (SMLRS).

RESULTS

The developed 58 pairs of polymorphic expressed sequence tag-simple sequence repeat (EST-SSR) markers from 959 candidate transcription factors (TFs) associated with yield were used for genotyping the 420 P. rockii accessions. We observed a high level of genetic diversity (polymorphic information content, PIC = 0.514) and low linkage disequilibrium (LD) between EST-SSRs. Moreover, four subpopulations in the association population were revealed by STRUCTURE analyses. Further, single-marker association analysis identified 141 significant associations, involving 17 quantitative traits and 41 EST-SSRs. These loci were mainly from AP2, TCP, MYB, HSF, bHLH, GATA, and B3 gene families and showed a small proportion of the phenotypic variance (3.79 to 37.45%).

CONCLUSIONS

Our results summarize a valuable collection of functional loci associated with yield traits in P. rockii, and provide a precious resource that reveals allelic variation underlying quantitative traits in Paeonia and other woody oil crops.

Comparative transcriptome and coexpression network analysis of carpel quantitative variation in Paeonia rockii

BACKGROUND

Quantitative variation of floral organs in plants is caused by an extremely complex process of transcriptional regulation. Despite progress in model plants, the molecular mechanisms of quantitative variation remain unknown in woody flower plants. The Paeonia rockii originated in China is a precious woody plant with ornamental, medicinal and oil properties. There is a wide variation in the number of carpel in P. rockii, but the molecular mechanism of the variation has rarely been studied. Then a comparative transcriptome was performed among two cultivars of P. rockii with different development patterns of carpel in this study.

RESULTS

Through the next-generation and single-molecule long-read sequencing (NGS and SMLRS), 66,563 unigenes and 28,155 differentially expressed genes (DEGs) were identified in P. rockii. Then clustering pattern and weighted gene coexpression network analysis (WGCNA) indicated that 15 candidate genes were likely involved in the carpel quantitative variation, including floral organ development, transcriptional regulatory and enzyme-like factors. Moreover, transcription factors (TFs) from the MYB, WD, RING1 and LRR gene families suggested the important roles in the management of the upstream genes. Among them, PsMYB114-like, PsMYB12 and PsMYB61-like from the MYB gene family were probably the main characters that regulated the carpel quantitative variation. Further, a hypothetical model for the regulation pattern of carpel quantitative variation was proposed in which the candidate genes function synergistically the quantitative variation process.

CONCLUSIONS

We present the high-quality sequencing products in P. rockii. Our results summarize a valuable collective of gene expression profiles characterizing the carpel quantitative variation. The DEGs are candidate for functional analyses of genes regulating the carpel quantitative variation in tree peonies, which provide a precious resource that reveals the molecular mechanism of carpel quantitative variation in other woody flower crops.

Maxent modeling for predicting the potential geographical distribution of two peony species under climate change

Paeonia (Paeoniaceae), an economically important plant genus, includes many popular ornamentals and medicinal plant species used in traditional Chinese medicine. Little is known about the properties of the habitat distribution and the important eco-environmental factors shaping the suitability. Based on high-resolution environmental data for current and future climate scenarios, we modeled the present and future suitable habitat for P. delavayi and P. rockii by Maxent, evaluated the importance of environmental factors in shaping their distribution, and identified distribution shifts under climate change scenarios. The results showed that the moderate and high suitable areas for P. delavayi and P. rockii encompassed ca. 4.46×10⁵km² and 1.89×10⁵km², respectively. Temperature seasonality and isothermality were identified as the most critical factors shaping P. delavayi distribution, and UVB-4 and annual precipitation were identified as the most critical for shaping P. rockii distribution. Under the scenario with a low concentration of greenhouse gas emissions (RCP2.6), the range of both species increased as global warming intensified; however, under the scenario with higher concentrations of emissions (RCP8.5), the suitable habitat range of P. delavayi decreased while P. rockii increased. Overall, our prediction showed that a shift in distribution of suitable habitat to higher elevations would gradually become more significant. The information gained from this study should provide a useful reference for implementing long-term conservation and management strategies for these species.

In Vitro and In Vivo Antioxidant Activities of the Flowers and Leaves from Paeonia rockii and Identification of Their Antioxidant Constituents by UHPLC-ESI-HRMSn via Pre-Column DPPH Reaction

The genus Paeonia, also known as the “King of Flowers” in China, is an important source of traditional Chinese medicine (TCM). Plants of this genus have been used to treat a range of cardiovascular and gynecological diseases. However, the potential pharmacological activity of one particular species, Paeonia rockii, has not been fully investigated. In the first part of the present study, 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic) acid (ABTS), reducing power assays, and metal ion chelating assays were used to investigate the in vitro antioxidant activities of Paeonia rockii. In the second portion of the study, a mouse model of d-galactose-induced aging was used to validate the antioxidant effects of the flowers from Paeonia rockii in vivo. Lastly, potential antioxidant constituents were screened and identified by ultra-high pressure liquid chromatography and electrospray ionization coupled with high-resolution mass spectrometry (UHPLC-ESI-HRMSⁿ) combined with the DPPH assay. Results indicated that the flowers and leaves exhibited stronger antioxidant activity than ascorbic acid in vitro. The therapeutic effect of Paeoniarockii was determined in relation to the levels of biochemical indicators, such as 8-iso-prostaglandin F_2α (8-iso PGF_2α) in the serum, superoxide dismutase (SOD), protein carbonyl, malondialdehyde (MDA), and glutathione (GSH) in the liver and brain, after daily intra-gastric administration of different concentrations of extracts (100, 200 and 400 mg/kg) for three weeks. The levels of 8-iso PGF_2α (p < 0.01) and protein carbonyl groups (p < 0.01) were significantly reduced, whereas those of SOD (p < 0.05) had significantly increased, indicating that components of the flowers of Paeonia rockii had favorable antioxidant activities in vivo. Furthermore, UHPLC-ESI-HRMSⁿ, combined with pre-column DPPH reaction, detected 25 potential antioxidant compounds. Of these, 18 compounds were tentatively identified, including 11 flavonoids, four phenolic acids, two tannins, and one monoterpene glycoside. This study concluded that the leaves and flowers from Paeonia rockii possess excellent antioxidant properties, highlighting their candidacy as “new” antioxidants, which can be utilized therapeutically to protect the body from diseases caused by oxidative stress.

Cloning, Characterization, and Expression Analysis of a Gene Encoding a Putative Lysophosphatidic Acid Acyltransferase from Seeds of Paeonia rockii

Tree peony (Paeonia section Moutan DC.) is an excellent woody oil crop, and the cloning and functional analysis of genes related to fatty acid (FA) metabolism from this organism has not been reported. Lysophosphatidic acid acyltransferase (LPAAT), which converts lysophosphatidic acid (LPA) to phosphatidic acid (PA), catalyzes the addition of fatty acyl moieties to the sn-2 position of the LPA glycerol backbone in triacylglycerol (TAG) biosynthesis. This project reports a putative lysophosphatidic acid acyltransferase gene PrLPAAT1 isolated from Paeonia rockii. Our data indicated that PrLPAAT1 has 1047 nucleotides and encodes a putative 38.8 kDa protein with 348 amino acid residues. Bioinformatic analysis demonstrated that PrLPAAT1 contains two transmembrane domains (TMDs). Subcellular localization analysis confirmed that PrLPAAT1 is a plasma membrane protein. Phylogenetic analysis revealed that PrLPAAT1 shared 74.3 and 65.5% amino acid sequence identities with the LPAAT1 sequences from columbine and grape, respectively. PrLPAAT1 belongs to AGPAT family, and may have acyltransferase activity. PrLPAAT1 was ubiquitously expressed in diverse tissues, and PrLPAAT1 expression was higher in the flower and developing seed. PrLPAAT1 is probably an important component in the FA accumulation process, especially during the early stages of seed development. PrLPAAT1 overexpression using a seed-specific promoter increased total FA content and the main FA accumulation in Arabidopsis transgenic plants.

Identification of Chemical Composition of Leaves and Flowers from Paeonia rockii by UHPLC-Q-Exactive Orbitrap HRMS

The Paeonia genus, an important source of crude drugs, has been extensively used in traditional Chinese medicine (TCM) to treat cardiovascular and female-related diseases. Although many peony species have been investigated, the study of Paeonia rockii is still quite limited, especially its chemical composition. Here, an advanced ultra-high-performance liquid chromatography (UHPLC) analytical technique combined with Q-Exactive Orbitrap hybrid quadrupole-Orbitrap mass spectrometry utilizing high-resolution full MS and MS/MS scan modes was applied to screen and identify the chemical constituents of this species. As a result, a total of 46 compounds were characterized, including 11 monoterpene glycosides, five phenolic acids, six tannins and 24 flavonoids. Among them, 16 compounds were reported for the first time in Paeonia rockii.