Brassinosteroids affect wood development and properties of Fraxinus mandshurica

IntroductionXylem development plays a crucial role in wood formation in woody plants. In recent years, there has been growing attention towards the impact of brassinosteroids (BRs) on this xylem development. In the present study, we evaluated the dynamic variation of xylem development in Fraxinus mandshurica (female parent, M8) and a novel interspecific hybrid F. mandshurica × Fraxinus sogdiana (1601) from May to August 2020.MethodsWe obtained RNA-Seq transcriptomes of three tissue types (xylem, phloem, and leaf) to identify the differences in xylem-differentially expressed genes (X-DEGs) and xylem-specifically expressed genes (X-SEGs) in M8 and 1601 variants. We then further evaluated these genes via weighted gene co-expression network analysis (WGCNA) alongside overexpressing FmCPD, a BR biosynthesis enzyme gene, in transient transgenic F. mandshurica.ResultsOur results indicated that the xylem development cycle of 1601 was extended by 2 weeks compared to that of M8. In addition, during the later wood development stages (secondary wall thickening) of 1601, an increased cellulose content (14%) and a reduced lignin content (11%) was observed. Furthermore, vessel length and width increased by 67% and 37%, respectively, in 1601 compared with those of M8. A total of 4589 X-DEGs were identified, including enzymes related to phenylpropane metabolism, galactose metabolism, BR synthesis, and signal transduction pathways. WGCNA identified hub X-SEGs involved in cellulose synthesis and BR signaling in the 1601 wood formation–related module (CESA8, COR1, C3H14, and C3H15); in contrast, genes involved in phenylpropane metabolism were significantly enriched in the M8 wood formation–related module (CCoAOMT and CCR). Moreover, overexpression of FmCPD in transient transgenic F. mandshurica affected the expression of genes associated with lignin and cellulose biosynthesis signal transduction. Finally, BR content was determined to be approximately 20% lower in the M8 xylem than in the 1601 xylem, and the exogenous application of BRs (24-epi brassinolide) significantly increased the number of xylem cell layers and altered the composition of the secondary cell walls in F. mandshurica.DiscussionOur findings suggest that BR biosynthesis and signaling play a critical role in the differing wood development and properties observed between M8 and 1601 F. mandshurica

Characteristics and Expression Analysis of <i>FmTCP15</i> under Abiotic Stresses and Hormones and Interact with DELLA Protein in <i>Fraxinus</i> <i>mandshurica</i> Rupr.

The TEOSINTE BRANCHED1, CYCLOIDEA, and PROLIFERATION CELL FACTOR (TCP) transcription factor is a plant-specific gene family and acts on multiple functional genes in controlling growth, development, stress response, and the circadian clock. In this study, a class I member of the TCP family from Fraxinus mandshurica Rupr. was isolated and named FmTCP15, which encoded a protein of 362 amino acids. Protein structures were analyzed and five ligand binding sites were predicted. The phylogenetic relationship showed that FmTCP15 was most closely related to Solanaceae and Plantaginaceae. FmTCP15 was localized in the nuclei of F. mandshurica protoplast cells and highly expressed in cotyledons. The expression pattern revealed the FmTCP15 response to multiple abiotic stresses and hormone signals. Downstream genes for transient overexpression of FmTCP15 in seedlings were also investigated. A yeast two-hybrid assay confirmed that FmTCP15 could interact with DELLA proteins. FmTCP15 participated in the GA-signaling pathway, responded to abiotic stresses and hormone signals, and regulated multiple genes in these biological processes. Our study revealed the potential value of FmTCP15 for understanding the molecular mechanisms of stress and hormone signal responses

DELLA-Mediated Gibberellin Acid Participation in the Regulation of Dormancy and Growth of <i>Fraxinus mandshurica</i> Rupr.

In Fraxinus mandshurica Rupr. (F. mandshurica), the mature seeds exhibit a deep dormancy trait, and the seedlings are vulnerable to external environmental factors, such as low temperature and drought, leading to ecological dormancy. In order to investigate the role of FmDELLA in growth and development, the variation in FmDELLA transcriptional level, the endogenous hormone content in seed germination and bud dormancy release, and the effects of the month, organs, and exogenous hormones on FmDELLA were determined. The results showed that FmDELLA genes had a synergistic impact with the XERICO, PP2C, and DOG genes on regulating hypocotyl elongation during seed germination. Unlike growing buds, the dormant buds had much higher levels of FmDELLA transcripts. Still, these transcript levels were lowered by using 100 mg/L exogenous gibberellin acid (GA), which could promote bud dormancy release. Exogenous hormones regulated the transcription of FmDELLA, which primarily occurred in the stems, leaves, buds, and flowers and reached its lowest level in September. The transition from dormancy to germination for buds and seeds was related to increased GA, auxin, and cytokinin and decreased abscisic acid. In conclusion, our study revealed the role of FmDELLA in the seed germination and release of bud dormancy and provided a solid basis for F. mandshurica tissue culture and micropropagation

Interspecific hybridizations of Fraxinus L. (F. mandshurica × F. americana and F. mandshurica × F. velutina) and heterosis analysis and selection of F1 progenies

The interspecific hybridizations of Fraxinus mandshurica Rupr. × Fraxinus americana L. (MA) and Fraxinus mandshurica × Fraxinus velutina Torr. (MV) were conducted to solve the problems of poor cold adaption associated with the introduction of Fraxinus in Heilongjiang province. High-voltage electrostatic field (HVEF) treatment to pollen was performed to overcome the prefertilization barriers. The hybrids adapted more strongly and grew better than the pure species (heterosis over higher parent (HHP) of the 9-year volume index was 5.5% for MA and 23.1% for MV) in Heilongjiang province. HVEF treatment greatly improved the number of seeds (0.25- to 5.52-fold) and seedlings (1.63- to 8.71-fold) of the hybrids. Additionally, three excellent female parents (nos. 15, 16, and 17) and seven hybrid combinations of MA (D94, D70, and D100) and MV (D103, D116, D105, and D104) with excellent growth traits were selected. The HHPs of volume index were 39.1%–112.5% for selected hybrids. Additionally, predicted growth trends of the hybrids showed that the hybrids will maintain a 7.7% to 9.3% height advantage over F. mandshurica through ages 10 to 15 years in Mao Ershan. These findings will accelerate the genetic breeding process of Fraxinus species.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Genome-Scale Transcriptome Analysis in Response to Nitric Oxide in Birch Cells: Implications of the Triterpene Biosynthetic Pathway

<div><p>Evidence supporting nitric oxide (NO) as a mediator of plant biochemistry continues to grow, but its functions at the molecular level remains poorly understood and, in some cases, controversial. To study the role of NO at the transcriptional level in <i>Betula platyphylla</i> cells, we conducted a genome-scale transcriptome analysis of these cells. The transcriptome of untreated birch cells and those treated by sodium nitroprusside (SNP) were analyzed using the Solexa sequencing. Data were collected by sequencing cDNA libraries of birch cells, which had a long period to adapt to the suspension culture conditions before SNP-treated cells and untreated cells were sampled. Among the 34,100 UniGenes detected, BLASTX search revealed that 20,631 genes showed significant (E-values≤10⁻⁵) sequence similarity with proteins from the NR-database. Numerous expressed sequence tags (i.e., 1374) were identified as differentially expressed between the 12 h SNP-treated cells and control cells samples: 403 up-regulated and 971 down-regulated. From this, we specifically examined a core set of NO-related transcripts. The altered expression levels of several transcripts, as determined by transcriptome analysis, was confirmed by qRT-PCR. The results of transcriptome analysis, gene expression quantification, the content of triterpenoid and activities of defensive enzymes elucidated NO has a significant effect on many processes including triterpenoid production, carbohydrate metabolism and cell wall biosynthesis.</p></div

Relative expression levels of genes related to cell wall synthesis in the groups treated with 1 mM SNP for 6, 12, 24, and 48 h (left).

<p>Relative expression levels of genes related to cell wall synthesis in SNP, KFeCN, and SNP + cPTIO (S + cPTIO) groups (right). Different letters represent significant difference (P<0.05).</p

Changes in antioxidant enzyme activities, including POD and APX among the control (CK), SNP, KFeCN, and SNP + cPTIO (S + cPTIO) groups.

<p>Different letters represent significant difference (P<0.05).</p

GO categories for the birch cell UniGenes.

<p>The percentage and total number of UniGenes in each category is shown.</p

Relative expression levels of genes related to triterpene synthesis in the groups treated with 1 mM SNP for 6, 12, 24, and 48 h (left).

<p>Relative expression levels of genes related to triterpene synthesis in the SNP, KFeCN, and SNP + cPTIO (S + cPTIO) groups (right). Different letters represent significant difference (P<0.05).</p

Changes in total triterpene and oleanolic acid content in the control (CK), SNP, KFeCN, and SNP + cPTIO (S + cPTIO) groups.

<p>Different letters represent significant difference (P<0.05).</p