EGTA reduces the inflorescence stem mechanical strength of herbaceous peony by modifying secondary wall biosynthesis

DIA-Based Phosphoproteomics Identifies Early Phosphorylation Events in Response to EGTA and Mannitol in Arabidopsis

Osmotic stress significantly hampers plant growth and crop yields, emphasizing the need for a thorough comprehension of the underlying molecular responses. Previous research has demonstrated that osmotic stress rapidly induces calcium influx and signaling, along with the activation of a specific subset of protein kinases, notably the Raf-like protein (RAF)-sucrose nonfermenting-1-related protein kinase 2 (SnRK2) kinase cascades within minutes. However, the intricate interplay between calcium signaling and the activation of RAF-SnRK2 kinase cascades remains elusive. Here, in this study, we discovered that Raf-like protein (RAF) kinases undergo hyperphosphorylation in response to osmotic shocks. Intriguingly, treatment with the calcium chelator EGTA robustly activates RAF-SnRK2 cascades, mirroring the effects of osmotic treatment. Utilizing high-throughput data-independent acquisition-based phosphoproteomics, we unveiled the global impact of EGTA on protein phosphorylation. Beyond the activation of RAFs and SnRK2s, EGTA treatment also activates mitogen-activated protein kinase cascades, Calcium-dependent protein kinases, and receptor-like protein kinases, etc. Through overlapping assays, we identified potential roles of mitogen-activated protein kinase kinase kinase kinases and receptor-like protein kinases in the osmotic stress-induced activation of RAF-SnRK2 cascades. Our findings illuminate the regulation of phosphorylation and cellular events by Ca2+ signaling, offering insights into the (exocellular) Ca2+ deprivation during early hyperosmolality sensing and signaling.

Side chain of confined xylan affects cellulose integrity leading to bending stem with reduced mechanical strength in ornamental plants

The stem support for fresh-cut flowers exerts a profound influence on the display of their blossoms. During vase insertion, bending stems significantly affect the ornamental value, but much remains unclear about the underlying reasons. In this study, six pairs of ornamental plants were screened for the contrast of bending and straight stems. The bending stems have weakened mechanical force and biomass recalcitrance compared with the straight ones. Meanwhile, cells in the bending stems became more loosely packed, along with a decrease in cell wall thickness and cellulose levels. Furthermore, wall properties characterizations show bending stems have decreased lignocellulosic CrI and cellulose DP, and enhanced the branching ratio of hemicellulose which is trapped in the cellulose. Given the distinct cell wall factors in different species, all data are grouped in standardized to eliminate the variations among plant species. The principal composition analysis and correlation analysis of the processed dataset strongly suggest that cellulose association factors determine the stem mechanical force and recalcitrance. Based on our results, we propose a model for how branches of confined hemicellulose interacted with cellulose to modulate stem strength support for the straight or bending phenotype in cut flowers.

Transcriptome and hormone metabolome reveal the mechanism of stem bending in water lily (Nymphaea tetragona) cut-flowers

Water lilies are popular ornamental cut-flowers with significant economic and cultural value. However, stem bending affects the preservation of cut-flowers during their vase life. To gain further insights into the molecular mechanisms of stem bending, transcriptome profiling, hormone measurement, and morphological analysis were performed using the stems of the 'Blue Bird' water lily. Transcriptome analysis revealed that 607 differentially expressed genes (DEGs) were associated with the dorsal and ventral stems of the water lily, of which 247 were up-regulated and 360 were down-regulated. Significant differences in genes associated with plant hormones, calcium ions, glucose metabolism, and photosynthesis pathways genes involved in the dorsal and ventral areas of the curved stem. In particular, DEGs were associated with the hormone synthesis, gravity response, starch granules, Ca2+ ions, and photosynthesis. The results of qRT-PCR were consistent with that of the transcriptome sequence analysis. A total of 12 hormones were detected, of which abscisic acid, indole-3-carboxaldehyde, indole-3-carboxaldehyde and jasmonic acid were significantly differentially expressed in the dorsal and ventral stems, and were significantly higher in the dorsal stem than in the ventral stem. The cell morphology in the dorsal and ventral areas of the curved stem clearly changed during vase life. The direction of starch granule settlement was consistent with the bending direction of the water lily stem, as well as the direction of gravity. In conclusion, stem bending in water lily cut-flowers is regulated by multiple factors and genes. This study provides an important theoretical basis for understanding the complex regulatory mechanism of water lily stem bending.

Effect of the pectin contents and nanostructure on the stem straightness of two Paeonia lactiflora cultivars

Herbaceous peony (Paeonia lactiflora Pall.) is an ancient ornamental crop and, in recent decades, an emerging popular cut flower. Straight stems are a vital criterion for cut herbaceous peony selection, while many cultivars bend as the plant develops. Pectin helps maintain the mechanical strength of the cell wall. However, little is known about its role in the stem bending of herbaceous peony. Two herbaceous peony cultivars with contrasting stem morphologies ('Dong Fang Shao Nv', upright; 'Lan Tian Piao Xiang', bending gradually) at five developmental stages were used as materials to investigate the effects of pectin content and nanostructure on straightness using the carbazole colorimetric method and atomic force microscopy observations. The contents of water-soluble pectin (WSP), CDTA-soluble pectin (CSP), and sodium carbonate-soluble pectin (SSP) differed significantly between the two cultivars, and the contents and angle of the flower and branch showed correlations. For the pectin nanostructure, WSP showed agglomerates and long chains, with a higher proportion of broad agglomerates at the later stages of the bending cultivar than the upright cultivar. CSP showed branched chains, and the proportion of broad chains was higher in the upright cultivar at later stages, while CSP shape changed from agglomerates to chains in the bending cultivar. SSP mainly consisted of short linear main chains, and side chains in the upright stem were stacked, and the bent cultivar had more broad and short chains. It can be concluded that the contents, nanometric shape, and size of the three kinds of pectin are highly likely to affect herbaceous peony stem straightness. This study provides a theoretical basis for the role of pectin in the production and breeding of herbaceous peony cut flowers.

Calcium-mediated rapid movements defend against herbivorous insects in Mimosa pudica

Animals possess specialized systems, e.g., neuromuscular systems, to sense the environment and then move their bodies quickly in response. Mimosa pudica, the sensitive plant, moves its leaves within seconds in response to external stimuli; e.g., touch or wounding. However, neither the plant-wide signaling network that triggers these rapid movements nor the physiological roles of the movements themselves have been determined. Here by simultaneous recording of cytosolic Ca²⁺ and electrical signals, we show that rapid changes in Ca²⁺ coupled with action and variation potentials trigger rapid movements in wounded M. pudica. Furthermore, pharmacological manipulation of cytosolic Ca²⁺ dynamics and CRISPR-Cas9 genome editing technology revealed that an immotile M. pudica is more vulnerable to attacks by herbivorous insects. Our findings provide evidence that rapid movements based on propagating Ca²⁺ and electrical signals protect this plant from insect attacks.

Transcriptome provides potential insights into how calcium affects the formation of stone cell in Pyrus

Background

The content of stone cells in pears has a great influence on taste. Stone cells are formed by the accumulation of lignin. The treatment of exogenous calcium can affect the lignin synthesis, but this Ca-mediated mechanism is still unclear. In this study, the author performed a comparative transcriptomic analysis of callus of pears (Pyrus x bretschneideri) treated with calcium nitrate Ca (NO₃)₂ to investigate the role of calcium in lignin synthesis.

Results

There were 2889 differentially expressed genes (DEGs) detected between the Control and Ca (NO₃)₂ treatment in total. Among these 2889 DEGs, not only a large number of genes related to Ca single were found, but also many genes were enriched in secondary metabolic pathway, especially in lignin synthesis. Most of them were up-regulated during the development of callus after Ca (NO₃)₂ treatment. In order to further explore how calcium nitrate treatment affects lignin synthesis, the author screened genes associated with transduction of calcium signal in DEGs, and finally found CAM, CML, CDPK, CBL and CIPK. Then the author identified the PbCML3 in pears and conducted relevant experiments finding the overexpression of PbCML3 would increase the content of pear stone cells, providing potential insights into how Ca treatment enhances the stone cell in pears.

Conclusions

Our deep analysis reveals the effects of exogenous calcium on calcium signal and lignin biosynthesis pathway. The function of PbCML3 on stone cells formation was verified in pear.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08161-5.

Silicon enhances stem strength by promoting lignin accumulation in herbaceous peony (Paeonia lactiflora Pall.)

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.

Comparative transcriptomic analysis of genes involved in stem lignin biosynthesis in woody and herbaceous Paeonia species

Paeonia is recognized globally due to its ornamental value. However, the mechanisms behind the formation of distinct levels of lignification in Paeonia stems remain largely unknown. In this study, we selected three representative Paeonia species, namely P. ostii (shrub), P. lactiflora (herb), and P. × 'Hexie' (semi-shrub), to evaluate and contrast their respective anatomical structure, phytochemical composition and transcriptomic profile. Our results showed that the degree of lignin deposition on the cell wall, along with the total amount of lignin and its monomers (especially G-lignin) were higher in P. ostii stems compared to the other two species at almost all development stages except 80 days after flowering. Furthermore, we estimated a total number of unigenes of 60,238 in P. ostii, 43,563 in P. × 'Hexie', and 40,212 in P. lactiflora from stem transcriptome. We then built a co-expression network of 25 transcription factors and 21 enzyme genes involved in lignin biosynthesis and identified nine key candidate genes. The expression patterns of these genes were positively correlated with the transcription levels of PAL, C4H, 4CL2, CCR, and COMT, as well as lignin content. Moreover, the highest relative expression levels of CCR, 4CL2, and C4H were found in P. ostii. This study provides an explanation for the observed differences in lignification between woody and herbaceous Paeonia stems, and constitutes a novel reference for molecular studies of stem-specific lignification process and lignin biosynthesis that can impact the ornamental industry.

Lignin provides mechanical support to herbaceous peony (Paeonia lactiflora Pall.) stems

Stem bending caused by mechanical failure is a major constraint for high-quality herbaceous peony (Paeonia lactiflora Pall.) cut flowers, but little is known about the underlying factors. In this study, two P. lactiflora cultivars, Xixia Yingxue (bending) and Hong Feng (upright), were used to investigate differences in stem bending. The results showed that the stem mechanical strength of Hong Feng was significantly higher than that of Xixia Yingxue, and the thickening of the secondary cell wall and the number of thickened secondary cell wall layers in Hong Feng were significantly higher than those in Xixia Yingxue. Moreover, compared with Xixia Yingxue, Hong Feng showed greater lignification of the cell wall and lignin deposition in the cell walls of the sclerenchyma, vascular bundle sheath and duct. All three types of lignin monomers were detected. The S-lignin, G-lignin, and total lignin contents and the activities of several lignin biosynthesis-related enzymes were higher in Hong Feng than in the other cultivar, and the S-lignin content was closely correlated with stem mechanical strength. In addition, 113,974 full-length isoforms with an average read length of 2106 bp were obtained from the full-length transcriptome of P. lactiflora stems, and differential expression analysis was performed based on the comparative transcriptomes of these two cultivars. Ten lignin biosynthesis-related genes, including 26 members that were closely associated with lignin content, were identified, and multiple upregulated and downregulated transcription factors were found to positively or negatively regulate lignin biosynthesis. Consequently, lignin was shown to provide mechanical support to P. lactiflora stems, providing useful information for understanding the formation of P. lactiflora stem strength.

Transcriptome analysis provides insights into the non-methylated lignin synthesis in Paphiopedilum armeniacum seed

BACKGROUNDS

Paphiopedilum is an important genus of the orchid family Orchidaceae and has high horticultural value. The wild populations are under threat of extinction because of overcollection and habitat destruction. Mature seeds of most Paphiopedilum species are difficult to germinate, which severely restricts their germplasm conservation and commercial production. The factors inhibiting germination are largely unknown.

RESULTS

In this study, large amounts of non-methylated lignin accumulated during seed maturation of Paphiopedilum armeniacum (P. armeniacum), which negatively correlates with the germination rate. The transcriptome profiles of P. armeniacum seed at different development stages were compared to explore the molecular clues for non-methylated lignin synthesis. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that a large number of genes associated with phenylpropanoid biosynthesis and phenylalanine metabolism during seed maturation were differentially expressed. Several key genes in the lignin biosynthetic pathway displayed different expression patterns during the lignification process. PAL, 4CL, HCT, and CSE upregulation was associated with C and H lignin accumulation. The expression of CCoAOMT, F5H, and COMT were maintained at a low level or down-regulated to inhibit the conversion to the typical G and S lignin. Quantitative real-time RT-PCR analysis confirmed the altered expression levels of these genes in seeds and vegetative tissues.

CONCLUSIONS

This work demonstrated the plasticity of natural lignin polymer assembly in seed and provided a better understanding of the molecular mechanism of seed-specific lignification process.

Color characteristics, pigment accumulation and biosynthetic analyses of leaf color variation in herbaceous peony (Paeonia lactiflora Pall.)

Herbaceous peony (Paeonia lactiflora Pall.) is one of the color-leaved ornamental spring plants, with graceful appearance and splendid color. However, the underlying mechanism of this coloration variation from purple to green has not been studied in P. lactiflora. In th study, the leaves in purple, purple-green, and green stages were compared in terms of anatomical, physiological, and molecular. We found that the variation of leaf color from purple to green was mainly determined by the change in pigments distributed in the leaf surface. Physiological experiments showed a significant increase in chlorophyll contents and a notable reduction in anthocyanin contents in leaves from the purple to green stages. We further found that the anthocyanin biosynthesis-related dihydroflavonol 4-reductase (DFR) gene and anthocyanin synthase (ANS) gene as well as chlorophyll biosynthesis-related glutamyl-tRNA reductase (HEMA) gene showed a decreased trend in leaves from purple to green stages, whereas the chlorophyll degradation-related chlorophyll b reductase (NYC) gene showed a rising trend. Alteration of DFR and ANS gene expression might reduce anthocyanin accumulation, whereas increased HEMA gene expression would enhance chlorophyll biosynthesis and reduced NYC gene expression would inhibit chlorophyll degradation. Consequently, reduction in anthocyanins and enhanced deposition of chlorophylls resulted in leaf coloration variation from purple to green in P. lactiflora, which could improve our understanding of its mechanism for further studies.

Transcriptome and weighted correlation network analyses provide insights into inflorescence stem straightness in Paeonia lactiflora

Lack of structural components results in inflorescence stem bending. Differentially expressed genes involved in lignin and hemicellulose biosynthesis are vital; genes involved in cellulose and glycan biosynthesis are also relevant. An erect inflorescence stem is essential for high-quality cut herbaceous peony flowers. To explore the factors underlying inflorescence stem bending, major cell walls contents were measured, and stem structure was observed in two herbaceous peony varieties with contrasting stem straightness traits ('Da Fugui', upright; 'Chui Touhong', bending). In addition, Illumina sequencing was performed and weighted correlation network analysis (WGCNA) was used to analyze the results. The results showed significant differences in lignin, hemicellulose and soluble sugar contents, sclerenchyma and xylem areas and thickening in cell walls in pith at stage S3, when bending begins. In addition, 44,182 significantly differentially expressed genes (DEGs) were found, and these DEGs were mainly enriched in 36 pathways. Among the DEGs, hub genes involved in lignin, cellulose, and xylan biosynthesis and transcription factors that regulated these process were identified by WGCNA. These results suggested that the contents of compounds that provided cell wall rigidity were vital factors affecting inflorescence stem straightness in herbaceous peony. Genes involved in or regulating the biosynthesis of these compounds are thus important; lignin and hemicellulose are of great interest, and cellulose and glycan should not be ignored. This paper lays a foundation for developing new herbaceous peony varieties suitable for cut flowers by molecular-assisted breeding.

Advances in molecular biology of Paeonia L

Molecular biology can serve as a tool to solve the limitations of traditional breeding and cultivation techniques related to flower patterns, the improvement of flower color, and the regulation of flowering and stress resistance. These characteristics of molecular biology ensured its significant role in improving the efficiency of breeding and germplasm amelioration of Paeonia. This review describes the advances in molecular biology of Paeonia, including: (1) the application of molecular markers; (2) genomics, transcriptomics, proteomics, metabolomics, and microRNA studies; (3) studies of functional genes; and (4) molecular biology techniques. This review also points out select limitations in current molecular biology, analyzes the direction of Paeonia molecular biology research, and provides advice for future research objectives.

Evaluating the Comprehensive Performance of Herbaceous Peonies at low latitudes by the Integration of Long-running Quantitative Observation and Multi-Criteria Decision Making Approach

Enlarging the planting area of economic plants, such as the "Southward Planting of Herbaceous Peony" (Paeonia lactiflora. Pall), is significant for improving people's lives. Peony is globally known as an ornamental because of gorgeous flowers and is mainly cultivated in the temperate regions with relatively cool and dry climates in the Northern Hemisphere. Promoting the landscape application of peony to the lower latitude regions is difficult because of the hot-humid climate. In this study, 29 northern peony cultivars and a unique Chinese southern peony, 'Hang Baishao', were introduced to Hangzhou, located in the central subtropics. Annual growth cycles, resistances and dormancy durations were measured, and crossbreeding between the southern and northern peonies was performed for six years, from 2012 to 2017. Based on data collected from the long-running quantitative observation (LQO), a multi-criteria decision making (MCDM) system was established to evaluate the comprehensive planting performance of these 30 cultivars in the central subtropics. 'Qihua Lushuang', 'Hang Baishao' and 'Meiju' were highly recommended, while 'Zhuguang' and 'Qiaoling' were scarcely recommended for the Hangzhou landscape. This study highlights the dependability and comprehensiveness of integrating the LQO and MCDM approaches for evaluating the introduction performance of ornamental plants.

Integrated analysis of transcriptomic and proteomic data from tree peony (P. ostii) seeds reveals key developmental stages and candidate genes related to oil biosynthesis and fatty acid metabolism

Tree peony (Paeonia section Moutan DC.) seeds are an excellent source of beneficial natural compounds that promote health, and they contain high levels of alpha-linolenic acid (ALA). In recent years, tree peony has been emerging as an oil crop. Therefore, combined analysis of the transcriptome and proteome of tree peony (P. ostii) seeds at 25, 32, 39, 53, 67, 81, 88, 95, and 109 days after pollination (DAP) was conducted to better understand the transcriptional and translational regulation of seed development and oil biosynthesis. A total of 38,482 unigenes and 2841 proteins were identified. A total of 26,912 differentially expressed genes (DEGs) and 592 differentially expressed proteins (DEPs) were clustered into three groups corresponding to the rapid growth, seed inclusion enrichment and conversion, and late dehydration and mature stages of seed development. Fifteen lipid metabolism pathways were identified at both the transcriptome and proteome levels. Pathway enrichment analysis revealed that a period of rapid fatty acid biosynthesis occurred at 53-88 DAP. Furthermore, 211 genes and 35 proteins associated with the fatty acid metabolism pathway, 63 genes and 11 proteins associated with the biosynthesis of unsaturated fatty acids (UFAs), and 115 genes and 24 proteins associated with ALA metabolism were identified. Phylogenetic analysis revealed that 16 putative fatty acid desaturase (FAD)-encoding genes clustered into four FAD groups, eight of which exhibited the highest expression at 53 DAP, suggesting that they play an important role in ALA accumulation. RT-qPCR analysis indicated that the temporal expression patterns of oil biosynthesis genes were largely similar to the RNA-seq results. The expression patterns of fatty acid metabolism- and seed development-related proteins determined by MRM were also highly consistent with the results obtained in the proteomic analysis. Correlation analysis indicated significant differences in the number and abundance of DEGs and DEPs but a high level of consistency in expression patterns and metabolic pathways. The results of the present study represent the first combined transcriptomic and proteomic analysis of tree peony seeds and provide insight into tree peony seed development and oil accumulation.