Genome-wide analysis of lncRNA and mRNA expression and endogenous hormone regulation during tension wood formation in Catalpa bungei

Comprehensive analysis of lncRNA-mRNA regulatory network in Populus associated with xylem development

Long noncoding RNAs (lncRNAs) play essential roles in numerous biological processes in plants, such as regulating the gene expression. However, only a few studies have looked into their potential functions in xylem development. High-throughput sequencing of P. euramericana 'Zhonglin46' developing and mature xylem was performed in this study. Through sequencing analysis, 14,028 putative lncRNA transcripts were identified, including 4525 differentially expressed lncRNAs (DELs). Additional research revealed that in mature xylem, a total of 2320 DELs were upregulated and 2205 were downregulated compared to developing xylem. Meanwhile, there were a total of 8122 differentially expressed mRNAs (DEMs) that were upregulated and 16,424 that were downregulated in mature xylem compared with developing xylem. The cis- and trans-target genes of DELs were analyzed for Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment, which indicated that these DELs participate in controlling the phenylpropanoid and lignin biosynthesis pathway as well as the starch and sucrose metabolism pathway. Among the cis-regulated DELs, LNC_006291, LNC_006292, and LNC_006532 all participate in regulating multiple HCT gene family membranes. As targets, POPTR_001G045900v3 (CCR2) and POPTR_018G063500v3 (SUS) both have only one cis-regulatory lncRNA, referred to as LNC_000057 and LNC_006212, respectively. Moreover, LNC_004484 and two DELs named LNC_008014 and LNC_010781 were revealed to be important nodes in the co-expression network of trans-lncRNAs and mRNAs associated to the lignin biosynthesis pathway and cellulose and xylan biosynthetic pathways, respectively. Finally, quantitative real-time PCR (qRT-PCR) was used to confirme 34 pairs of lncRNA-mRNA. Taken together, these findings may help to clarify the regulatory role that lncRNAs play in xylem development and wood formation.

Comprehensive Transcriptome Analysis of Stem-Differentiating Xylem Upon Compression Stress in Cunninghamia Lanceolata

Compression wood (CW) in gymnosperm brings great difficulties to wood industry using wood as raw materials since CW presents special wood structure and have different physical and chemical properties from those of normal wood (NW). Chinese fir (Cunninghamia lanceolata) is widely distributed in China. However, global transcriptome profiling of coding and long non-coding RNA in response to compression stress has not been reported in the gymnosperm species. In this study, we revealed that CW in Chinese fir exhibited distinct morphology and cytology properties compared with those of NW, including high lignin content, thick and round tracheid cells. Furthermore, we combined both PacBio long-read SMRT sequencing (Iso-Seq) and Illumina short-read RNA-Seq to reveal the transcriptome in stem-differentiating xylem (SDX) under different time points (2, 26, and 74 h) upon compression stress in NW, CW, and OW (opposite wood), respectively. Iso-Seq was successfully assembled into 41,253 de-novo full-length transcriptome reference (average length 2,245 bp). Moreover, there were striking differences in expression upon compression stress, which were involved 13 and 7 key enzyme genes in the lignin and cellulose synthesis, respectively. Especially, we revealed 11 secondary growth-related transcription factors show differential expression under compression stress, which was further validated by qRT-PCR. Finally, the correlation between 6,533 differentially expressed coding genes and 372 differentially expressed long non-coding RNAs (lncRNAs) indicates that these lncRNAs may affect cell wall biogenesis and xyloglucan metabolism. In conclusion, our results provided comprehensive cytology properties and full-length transcriptome profiling of wood species upon compression stress. Especially we explored candidate genes, including both coding and long non-coding genes, and provided a theoretical basis for further research on the formation mechanism of CW in gymnosperm Chinese fir.

Comprehensive Analysis of Long Non-coding RNA Modulates Axillary Bud Development in Tobacco (Nicotiana tabacum L.)

Long non-coding RNAs (lncRNAs) regulate gene expression and are crucial for plant growth and development. However, the mechanisms underlying the effects of activated lncRNAs on axillary bud development remain largely unknown. By lncRNA transcriptomes of axillary buds in topped and untopped tobacco plants, we identified a total of 13,694 lncRNAs. LncRNA analysis indicated that the promoted growth of axillary bud by topping might be partially ascribed to the genes related to hormone signal transduction and glycometabolism, trans-regulated by differentially expressed lncRNAs, such as MSTRG.52498.1, MSTRG.60026.1, MSTRG.17770.1, and MSTRG.32431.1. Metabolite profiling indicated that auxin, abscisic acid and gibberellin were decreased in axillary buds of topped tobacco lines, while cytokinin was increased, consistent with the expression levels of related lncRNAs. MSTRG.52498.1, MSTRG.60026.1, MSTRG.17770.1, and MSTRG.32431.1 were shown to be influenced by hormones and sucrose treatments, and were associated with changes of axillary bud growth in the overexpression of NtCCD8 plants (with reduced axillary buds) and RNA interference of NtTB1 plants (with increased axillary buds). Moreover, MSTRG.28151.1 was identified as the antisense lncRNA of NtTB1. Silencing of MSTRG.28151.1 in tobacco significantly attenuated the expression of NtTB1 and resulted in larger axillary buds, suggesting the vital function of MSTRG.28151.1 axillary bud developmen by NtTB1. Our findings shed light on lncRNA-mRNA interactions and their functional roles in axillary bud growth, which would improve our understanding of lncRNAs as important regulators of axillary bud development and plant architecture.

Non-Coding RNA Analyses of Seasonal Cambium Activity in Populus tomentosa

Non-coding RNA, known as long non-coding RNA (lncRNA), circular RNA (circRNA) and microRNA (miRNA), are taking part in the multiple developmental processes in plants. However, the roles of which played during the cambium activity periodicity of woody plants remain poorly understood. Here, lncRNA/circRNA-miRNA-mRNA regulatory networks of the cambium activity periodicity in Populus tomentosa was constructed, combined with morphologic observation and transcriptome profiling. Light microscopy and Periodic Acid Schiff (PAS) staining revealed that cell walls were much thicker and number of cell layers was increased during the active-dormant stage, accompanied by abundant change of polysaccharides. The novel lncRNAs and circRNAs were investigated, and we found that 2037 lncRNAs and 299 circRNAs were differentially expression during the vascular cambium period, respectively. Moreover, 1046 genes were identified as a target gene of 2037 novel lncRNAs, and 89 of which were the miRNA precursors or targets. By aligning miRNA precursors to the 7655 lncRNAs, 21 lncRNAs were identified as precursors tof 19 known miRNAs. Furthermore, the target mRNA of lncRNA/circRNA-miRNA network mainly participated in phytohormone, cell wall alteration and chlorophyll metabolism were analyzed by GO enrichment and KEGG pathway. Especially, circRNA33 and circRNA190 taking part in the phytohormone signal pathway were down-regulated during the active-dormant transition. Xyloglucan endotransglucosylase/hydrolase protein 24-like and UDP-glycosyltransferase 85A1 involved in the cell wall modification were the targets of lncRNA MSTRG.11198.1 and MSTRG.1050.1. Notably, circRNA103 and MSTRG.10851.1 regulate the cambium periodicity may interact with the miR482. These results give a new light into activity–dormancy regulation, associated with transcriptional dynamics and non-coding RNA networks of potential targets identification.

Genome-Wide Identification of Long Non-Coding RNAs and Their Potential Functions in Poplar Growth and Phenylalanine Biosynthesis

Poplar is an important bioenergy tree species. lncRNAs play important roles in various biological regulatory processes, and their expression pattern is more tissue-specific than mRNAs. In this study, P. deltoides “Danhong” (Pd) and P. simonii “Tongliao1” (Ps) with different growth rates and wood quality were used as experimental materials, and the transcriptomes of their shoot apical meristem, xylem, and phloem were sequenced. Furthermore, high-throughput RNA sequencing analysis revealed that the expression patterns of genes and lncRNAs are different between the two genotypes. 6,355 lncRNAs were identified. Based on target prediction, lncRNAs and target genes were involved in ADP binding, oxidoreductase activity, phenylpropanoid biosynthesis, and cyanoamino acid metabolism. The DElncRNAs in two poplars were co-expressed with transcription factors and structural genes of lignin and flavonoid pathways. In addition, we found the potential target lncRNAs of miRNA. This result provides basic evidence for a better understanding of the regulatory role of lncRNAs in regulating phenylalanine molecular pathways and wood formation.

RNA Sequencing Reveals Phenylpropanoid Biosynthesis Genes and Transcription Factors for Hevea brasiliensis Reaction Wood Formation

Given the importance of wood in many industrial applications, much research has focused on wood formation, especially lignin biosynthesis. However, the mechanisms governing the regulation of lignin biosynthesis in the rubber tree (Hevea brasiliensis) remain to be elucidated. Here, we gained insight into the mechanisms of rubber tree lignin biosynthesis using reaction wood (wood with abnormal tissue structure induced by gravity or artificial mechanical treatment) as an experimental model. We performed transcriptome analysis of rubber tree mature xylem from tension wood (TW), opposite wood (OW), and normal wood (NW) using RNA sequencing (RNA-seq). A total of 214, 1,280, and 32 differentially expressed genes (DEGs) were identified in TW vs. NW, OW vs. NW, and TW vs. OW, respectively. GO and KEGG enrichment analysis of DEGs from different comparison groups showed that zeatin biosynthesis, plant hormone signal transduction, phenylpropanoid biosynthesis, and plant-pathogen interaction pathways may play important roles in reaction wood formation. Sixteen transcripts involved in phenylpropanoid biosynthesis and 129 transcripts encoding transcription factors (TFs) were used to construct a TF-gene regulatory network for rubber tree lignin biosynthesis. Among them, MYB, C2H2, and NAC TFs could regulate all the DEGs involved in phenylpropanoid biosynthesis. Overall, this study identified candidate genes and TFs likely involved in phenylpropanoid biosynthesis and provides novel insights into the mechanisms regulating rubber tree lignin biosynthesis.