Search

SUMMARY: Stem strength is an important agronomic trait affecting plant lodging, and plays an essential role in the quality and yield of plants. Thickened secondary cell walls in stems provide mechanical strength that allows plants to stand upright, but the regulatory mechanism of secondary cell wall thickening and stem strength in cut flowers remains unclear. In this study, first, a total of 11 non‐redundant Paeonia lactiflora R2R3‐MYBs related to stem strength were identified and isolated from cut‐flower herbaceous peony, among which PlMYB43, PlMYB83 and PlMYB103 were the most upregulated differentially expressed genes. Then, the expression characteristics revealed that these three R2R3‐MYBs were specifically expressed in stems and acted as transcriptional activators. Next, biological function verification showed that these P. lactiflora R2R3‐MYBs positively regulated stem strength, secondary cell wall thickness and lignin deposition. Furthermore, yeast‐one‐hybrid and dual luciferase reporter assays demonstrated that they could bind to the promoter of caffeic acid O‐methyltransferase gene (PlCOMT2) and/or laccase gene (PlLAC4), two key genes involved in lignin biosynthesis. In addition, the function of PlLAC4 in increasing lignin deposition was confirmed by virus‐induced gene silencing and overexpression. Moreover, PlMYB83 could also act as a transcriptional activator of PlMYB43. The findings of the study propose a regulatory network of R2R3‐MYBs modulating lignin biosynthesis and secondary cell wall thickening for improving stem lodging resistance, and provide a resource for molecular genetic engineering breeding of cut flowers. [ABSTRACT FROM AUTHOR]

Herbaceous peony (Paeonia lactiflora Pall.) is an ornamental plant with huge potential in the international flower market. Similar to the flowers of most other ornamental plants, the top sellers of P. lactiflora are those with red or pink flowers. However, most studies on flower colors have focused on the novel colors and have neglected the most common red flowers. In this study, a red cultivar of P. lactiflora ('Dafugui') and a pink cultivar ('Qingwen') were selected in order to study the discrepancy in the red color of the flowers. The results demonstrate that these two cultivars have the same compositions as anthocyanins, flavones, and flavonols but different contents. 'Dafugui' was found to have a high accumulation of upstream substances due to the higher expression of the early genes encoding phenylalanine ammonialyase (PlPAL) and flavonoid 3′-hydroxylase (PlF3′H). Moreover, the anthocyanidin synthase gene (PlANS) and UDP-glucose flavonoid 3-O-glucosyltransferase gene (PlUF3GT) encoding enzymes catalyze these upstream substances into anthocyanins, resulting in more redness in 'Dafugui' than in 'Qingwen'. Our study thus provides a better understanding of the anthocyanin accumulation and coloring mechanism of P. lactiflora and can serve as a theoretical basis for breeding more red flowers using genetic engineering techniques to cater to consumers' preferences. [ABSTRACT FROM AUTHOR]

The shading treatment which decreases light intensity affects the ornamental characteristics in herbaceous peony (Paeonia lactiflora Pall.), including flower color, leaf shape and stem straightness. However, the morphological, microstructural and lignin-related responses of its stems to shading have not been systematically and deeply studied. Here, we focused on these responses to shading treatment in herbaceous peony stems. Morphological results showed that shading treatment significantly bended stems, decreased stem diameters, lightened stem weights and reduced stem strength. Microstructural observations demonstrated that shading treatment decreased vascular bundle number, xylem area, xylem ratio and secondary cell wall (SCW) thickness. Lignin-related analysis revealed that shading treatment markedly decreased lignin content in cell walls especially S-lignin and G-lignin, deposition in SCWs and related enzyme activities. Furthermore, transcriptomic analysis showed that shading treatment suppressed lignin-related processes, lignin biosynthetic pathway and lignin-related transcriptional activators. Collectively, shading treatment suppressed lignin biosynthesis and reduced lignin deposition in SCW, leading to undeveloped secondary xylem and bender stems. These findings provide a fundamental understanding of the morphological, microstructural and lignin-related responses of herbaceous peony stem to shading. • Shading treatment led to slender and bender stems in herbaceous peony. • Shading treatment inhibited xylem and SCW development, resulting in bender stems. • Shading treatment reduced lignin content, deposition, composition and related enzyme activities. • Shading treatment suppressed lignin biosynthesis and its transcriptional regulation. [ABSTRACT FROM AUTHOR]

Daminozide is a plant growth retardant that inhibits 2-oxoglutarate-dependent dioxygenase activity in the gibberellin biosynthesis pathway, but few studies have focused on its effect on the flavonoid biosynthesis pathway involved in flower color. In the present study, the effect of daminozide on the regulation of flower color was investigated. An herbaceous peony (Paeonia lactiflora Pall.) cultivar ‘Fenzhu Pan’ was used as the material and treated with daminozide. Color parameters of petals were measured; flavonoid composition and content as well as flavonoid biosynthetic gene expression were monitored. The results showed that daminozide treatment caused less red coloration in herbaceous peony. The content of total anthocyanins was decreased by 23%, and the content of total anthoxanthins was increased by 8%; thus, it appeared that less red coloration in daminozide-treated flowers was associated with restricted anthocyanin accumulation. Furthermore, the gene expression patterns of flavonoid 3′-hydroxylase, dihydroflavonol 4-reductase and anthocyanidin synthase were lower after daminozide treatment, which could decrease anthocyanin accumulation and lead to less red coloration in flowers. These findings would improve our understanding of daminozide regulation of flower color in herbaceous peony. [ABSTRACT FROM AUTHOR]

Herbaceous peony (Paeonia lactiflora Pall.) is a popular high-end cut flower, but stem bending caused by low stem strength severely decreases its quality. To enhance stem strength, the regulatory effects of exogenous silicon were investigated in P. lactiflora. The results showed that silicon application enhanced stem strength by increasing the thickness of secondary cell walls and the layers of thickened secondary cells. Moreover, more lignin accumulated, particularly G-lignin and S-lignin, and the activities of lignin biosynthetic enzymes increased with silicon application. In addition, based on transcriptome analysis, silicon application induced the expression of genes participating in lignin biosynthesis pathway. Among them, hydroxycinnamoyl-CoA: shikimate hydroxycinnamoyl transferase gene (HCT1) was isolated from P. lactiflora and found to be mainly localized in the cytoplasm of cells. Overexpression of PlHCT1 increased the layers of thickened secondary cells and lignin accumulation in tobacco, resulting in enhanced stem strength and demonstrably straight stems. Finally, silicon content, lignin content and PlHCT1 expression in P. lactiflora cultivars with high stem strengths were totally higher than those in cultivars with low stem strengths. These results indicated that silicon application enhanced stem strength by promoting lignin accumulation in P. lactiflora , which has prospects for stem quality improvement in general. [Display omitted] • Silicon increased the net photosynthesis rate and SPAD value. • Silicon enhanced stem strength by promoting lignin accumulation. • Silicon increased lignin biosynthetic enzyme activities and gene expression. • HCT1 expression was induced and localized in the cytoplasm of cells. • Overexpression of HCT1 increased lignin, resulting in enhanced stem strength. [ABSTRACT FROM AUTHOR]

• Herbaceous peony stem diameter could be used to estimate stem strength. • Thickness of secondary cell wall contributed a lot to stem strength. • Three lignin monomers affected herbaceous peony stem strength. • Lignin deposition and secondary cell wall of the stem were observed. • CAD was a key gene controlling herbaceous peony lignin accumulation. Straight stems are highly important to herbaceous peony (Paeonia lactiflora Pall.) cut flowers. To clarify whether the microstructural and lignin characteristics are associated with P. lactiflora stem mechanical strength, eight cultivars were used to study their anatomical structure, secondary cell wall, lignin deposition, lignin content and structure, lignin biosynthetic enzyme activity and related gene expression levels. The results showed that stem diameter was a direct indicator estimating its mechanical strength. Simultaneously, the number of vascular bundles, area of vascular bundles, number of duct perforations, ratio of xylem to cross-section and thickness of secondary cell wall had significant positive correlations with stem mechanical strength. Moreover, three lignin monomers were all detected in the stem, and the contents of S-lignin, G-lignin and total lignin in high stem mechanical strength cultivars were higher than those in low stem mechanical strength cultivars as a whole, and lignin was deposited in the cell walls of the sclerenchyma, vascular bundle sheath and duct. Additionally, cinnamate 4-hydroxylase (C4H), cinnamyl alcohol dehydrogenase (CAD) and polyphenol oxidase (PPO) activities in high stem mechanical strength cultivars were higher than those in low stem mechanical strength cultivars as a whole, and CAD might be the key gene among detected lignin biosynthetic genes. Consequently, microstructural and lignin characteristics were closely correlated with stem mechanical strength in P. lactiflora. These results would provide useful information concerning the physiological mechanism of stem strength. [ABSTRACT FROM AUTHOR]