The association of hormone signalling genes, transcription and changes in shoot anatomy during moso bamboo growth

Bulbil initiation: a comprehensive review on resources, development, and utilisation, with emphasis on molecular mechanisms, advanced technologies, and future prospects

Bulbil is an important asexual reproductive structure of bulbil plants. It mainly grows in leaf axils, leaf forks, tubers and the upper and near ground ends of flower stems of plants. They play a significant role in the reproduction of numerous herbaceous plant species by serving as agents of plant propagation, energy reserves, and survival mechanisms in adverse environmental conditions. Despite extensive research on bulbil-plants regarding their resources, development mechanisms, and utilisation, a comprehensive review of bulbil is lacking, hindering progress in exploiting bulbil resources. This paper provides a systematic overview of bulbil research, including bulbil-plant resources, identification of development stages and maturity of bulbils, cellular and molecular mechanisms of bulbil development, factors influencing bulbil development, gene research related to bulbil development, multi-bulbil phenomenon and its significance, medicinal value of bulbils, breeding value of bulbils, and the application of plant tissue culture technology in bulbil production. The application value of the Temporary Immersion Bioreactor System (TIBS) and Terahertz (THz) in bulbil breeding is also discussed, offering a comprehensive blueprint for further bulbil resource development. Additionally, additive, seven areas that require attention are proposed: (1) Utilization of modern network technologies, such as plant recognition apps or websites, to collect and identify bulbous plant resources efficiently and extensively; (2) Further research on cell and tissue structures that influence bulb cell development; (3) Investigation of the network regulatory relationship between genes, proteins, metabolites, and epigenetics in bulbil development; (4) Exploration of the potential utilization value of multiple sprouts, including medicinal, ecological, and horticultural applications; (5) Innovation and optimization of the plant tissue culture system for bulbils; (6) Comprehensive application research of TIBS for large-scale expansion of bulbil production; (7) To find out the common share genetics between bulbils and flowers.

Genome-wide analysis of the KNOX gene family in Moso bamboo: insights into their role in promoting the rapid shoot growth

BACKGROUND

KNOTTED1-like homeobox (KNOX) genes, plant-specific homologous box transcription factors (TFs), play a central role in regulating plant growth, development, organ formation, and response to biotic and abiotic stresses. However, a comprehensive genome-wide identification of the KNOX genes in Moso bamboo (Phyllostachys edulis), the fastest growing plant, has not yet been conducted, and the specific biological functions of this family remain unknown.

RESULTS

The expression profiles of 24 KNOX genes, divided into two subfamilies, were determined by integrating Moso bamboo genome and its transcriptional data. The KNOX gene promoters were found to contain several light and stress-related cis-acting elements. Synteny analysis revealed stronger similarity with rice KNOX genes than with Arabidopsis KNOX genes. Additionally, several conserved structural domains and motifs were identified in the KNOX proteins. The expansion of the KNOX gene family was primarily regulated by tandem duplications. Furthermore, the KNOX genes were responsive to naphthaleneacetic acid (NAA) and gibberellin (GA) hormones, exhibiting distinct temporal expression patterns in four different organs of Moso bamboo. Short Time-series Expression Miner (STEM) analysis and quantitative real-time PCR (qRT-PCR) assays demonstrated that PeKNOX genes may play a role in promoting rapid shoot growth. Additionally, Gene Ontology (GO) and Protein-Protein Interaction (PPI) network enrichment analyses revealed several functional annotations for PeKNOXs. By regulating downstream target genes, PeKNOXs are involved in the synthesis of AUX /IAA, ultimately affecting cell division and elongation.

CONCLUSIONS

In the present study, we identified and characterized a total of 24 KNOX genes in Moso bamboo and investigated their physiological properties and conserved structural domains. To understand their functional roles, we conducted an analysis of gene expression profiles using STEM and RNA-seq data. This analysis successfully revealed regulatory networks of the KNOX genes, involving both upstream and downstream genes. Furthermore, the KNOX genes are involved in the AUX/IAA metabolic pathway, which accelerates shoot growth by influencing downstream target genes. These results provide a theoretical foundation for studying the molecular mechanisms underlying the rapid growth and establish the groundwork for future research into the functions and transcriptional regulatory networks of the KNOX gene family.

Deciphering the regulatory role of PheSnRK genes in Moso bamboo: insights into hormonal, energy, and stress responses

The SnRK (sucrose non-fermentation-related protein kinase) plays an important role in regulating various signals in plants. However, as an important bamboo shoot and wood species, the response mechanism of PheSnRK in Phyllostachys edulis to hormones, low energy and stress remains unclear. In this paper, we focused on the structure, expression, and response of SnRK to hormones and sugars. In this study, we identified 75 PheSnRK genes from the Moso bamboo genome, which can be divided into three groups according to the evolutionary relationship. Cis-element analysis has shown that the PheSnRK gene can respond to various hormones, light, and stress. The PheSnRK2.9 proteins were localized in the nucleus and cytoplasm. Transgenic experiments showed that overexpression of PheSnRK2.9 inhibited root development, the plants were salt-tolerant and exhibited slowed starch consumption in Arabidopsis in the dark. The results of yeast one-hybrid and dual luciferase assay showed that PheIAAs and PheNACs can regulate PheSnRK2.9 gene expression by binding to the promoter of PheSnRK2.9. This study provided a comprehensive understanding of PheSnRK genes of Moso bamboo, which provides valuable information for further research on energy regulation mechanism and stress response during the growth and development of Moso bamboo.

Mysterious Bamboo flowering phenomenon: A literature review and new perspectives

Bamboo, a globally distributed non-timber forest resource, plays a critical role in local ecosystems and economies. Despite its significance, the understanding of bamboo's long and unpredictable flowering cycles remains limited. Our bibliometric analysis of bamboo flowering-related literature from the Web of Science database reveals an initial focus on regeneration studies, with a recent trend shifting towards microscopic and molecular perspectives. Furthermore, our narrative review emphasizes the importance of considering factors such as the proportion of flowering culms and the duration of flowering in classifying bamboo flowering phenomena. While numerous studies have endorsed the predator saturation hypothesis as a suitable explanation for the synchronicity of bamboo flowering, no existing theory explains bamboo's prolonged flowering cycles. We propose a new natural selection hypothesis as a potential explanation for these extraordinary cycles, underscoring the need for further research in this area. Despite the substantial volume of data accumulated on bamboo flowering, these resources have not been fully exploited in recent research. Future studies would benefit from more comprehensive data collection methods, encompassing field observations, satellite remote sensing data, and omics data. The convergence of traditional ecological studies with molecular techniques may pave the way for significant advancements in bamboo flowering research.

Chromosomal-level genome and metabolome analyses of highly heterozygous allohexaploid Dendrocalamus brandisii elucidate shoot quality and developmental characteristics

Dendrocalamus brandisii (Munro) Kurz is a sympodial bamboo species with inimitable taste and flavorful shoots. Its rapid growth and use as high-quality material make this bamboo species highly valued for both food processing and wood applications. However, genome information for D. brandisii is lacking, primarily due to its polyploidy and large genome size. Here, we assembled a high-quality genome for hexaploid D. brandisii, which comprises 70 chromosomes with a total size of 2,756 Mb, using long-read HiFi sequencing. Furthermore, we accurately separated the genome into its three constituent subgenomes. We used Oxford Nanopore Technologies long reads to construct a transcriptomic dataset covering 15 tissues for gene annotation to complement our genome assembly, revealing differential gene expression and post-transcriptional regulation. By integrating metabolome analysis, we unveiled that well-balanced lignin formation, as well as abundant flavonoid and fructose contents, contribute to the superior quality of D. brandisii shoots. Integrating genomic, transcriptomic, and metabolomic datasets provided a solid foundation for enhancing bamboo shoot quality and developing efficient gene-editing techniques. This study should facilitate research on D. brandisii and enhance its use as a food source and wood material by providing crucial genomic resources.

Anatomical and Transcriptome Analyses of Moso Bamboo Culm Neck Growth: Unveiling Key Insights

The Moso bamboo culm neck, connected with the rhizome and the shoot bud, is an important hub for connecting and transporting the aboveground and belowground systems of bamboo for the shoot bud development and rapid growth. Our previous study revealed that the culm neck generally undergoes six different developmental stages (CNS1-CNS6), according to the primary thickening growth of the underground shoot bud. However, the molecular mechanism of the culm neck development remains unknown. The present study focused on the developmental process of the CNS3-CNS5 stages, representing the early, middle, and late elongation stages, respectively. These stages are densely packed with vascular tissues and consist of epidermis, hypodermis, cortex, and ground tissue. Unlike the hollow structure of the culms, the culm necks are solid structures. As the culm neck continues to grow, the lignin deposition increases noticeably, contributing to its progressive strengthening. For the transcriptome analysis, a total of 161,160 transcripts with an average length of 2373 were obtained from these stages using both PacBio and Illumina sequencing. A total of 92.2% of the reads mapped to the Moso bamboo reference genome. Further analysis identified a total of 5524 novel genes and revealed a dynamic transcriptome. Secondary-metabolism- and transport-related genes were upregulated particularly with the growth of the culm neck. Further analysis revealed the molecular processes of lignin accumulation in the culm neck, which include differentially expressed genes (DEGs) related to cell wall loosening and remodeling and secondary metabolism. Moreover, the upregulations of transcription factors such as MYBH and RSM in the MYB family play crucial roles during critical transitions in the culm neck development, such as changes in the angle between the rhizome and the culm neck. Our new findings provide essential insights into the cellular roadmaps, transcriptional networks, and key genes involved in the culm neck development.

Inhibition of DNA and RNA methylation disturbs root development of moso bamboo

DNA methylation (5mC) and N6-methyladenosine (m6A) are two important epigenetics regulators, which have a profound impact on plant growth development. Phyllostachys edulis (P. edulis) is one of the fastest spreading plants due to its well-developed root system. However, the association between 5mC and m6A has seldom been reported in P. edulis. In particular, the connection between m6A and several post-transcriptional regulators remains uncharacterized in P. edulis. Here, our morphological and electron microscope observations showed the phenotype of increased lateral root under RNA methylation inhibitor (DZnepA) and DNA methylation inhibitor (5-azaC) treatment. RNA epitranscriptome based on Nanopore direct RNA sequencing revealed that DZnepA treatment exhibits significantly decreased m6A level in the 3'-untranslated region (3'-UTR), which was accompanied by increased gene expression, full-length ratio, higher proximal poly(A) site usage and shorter poly(A) tail length. DNA methylation levels of CG and CHG were reduced in both coding sequencing and transposable element upon 5-azaC treatment. Cell wall synthesis was impaired under methylation inhibition. In particular, differentially expressed genes showed a high percentage of overlap between DZnepA and 5-azaC treatment, which suggested a potential correlation between two methylations. This study provides preliminary information for a better understanding of the link between m6A and 5mC in root development of moso bamboo.

Insight into gene expression associated with DNA methylation and small RNA in the rhizome-root system of Moso bamboo

Moso bamboo (Phyllostachys edulis), typically a monopodial scattering bamboo, is famous for its rapid growth. The rhizome-root system of Moso bamboo plays a crucial role in its clonal growth and spatial distribution. However, few studies have focused on rhizome-root systems. Here we collected LBs, RTs, and RGFNSs, the most important parts of the rhizome-root system, to study the molecular basis of the rapid growth of Moso bamboo due to epigenetic changes, such as DNA modifications and small RNAs. The angle of the shoot apical meristem of LB gradually decreased with increasing distance from the mother plant, and the methylation levels of LB were much higher than those of RT and RGFNS. 24 nt small RNAs and mCHH exhibited similar distribution patterns in transposable elements, suggesting a potential association between these components. The miRNA abundance of LB gradually increased with increasing distance from the mother plant, and a negative correlation was observed between gene expression levels and mCG and mCHG levels in the gene body. This study paves the way for further exploring the effects of epigenetic factors on the physiology of Moso bamboo.

GA20ox Family Genes Mediate Gibberellin and Auxin Crosstalk in Moso bamboo (Phyllostachys edulis)

Moso bamboo (Phyllostachys edulis) is one of the fastest growing plants. Gibberellin (GA) is a key phytohormone regulating growth, but there are few studies on the growth of Moso bamboo regulated by GA. The gibberellin 20 oxidase (GA20ox) gene family was targeted in this study. Chromosomal distribution and collinearity analysis identified 10 GA20ox genes evenly distributed on chromosomes, and the family genes were relatively conservative in evolution. The genetic relationship of GA20ox genes had been confirmed to be closest in different genera of plants in a phylogenetic and selective pressure analysis between Moso bamboo and rice. About 1/3 GA20ox genes experienced positive selective pressure with segmental duplication being the main driver of gene family expansion. Analysis of expression patterns revealed that only six PheGA20ox genes were expressed in different organs of shoot development and flowers, that there was redundancy in gene function. Underground organs were not the main site of GA synthesis in Moso bamboo, and floral organs are involved in the GA biosynthesis process. The auxin signaling factor PheARF47 was located upstream of PheGA20ox3 and PheGA20ox6 genes, where PheARF47 regulated PheGA20ox3 through cis-P box elements and cis-AuxRR elements, based on the result that promoter analysis combined with yeast one-hybrid and dual luciferase detection analysis identified. Overall, we identified the evolutionary pattern of PheGA20ox genes in Moso bamboo and the possible major synthesis sites of GA, screened for key genes in the crosstalk between auxin and GA, and laid the foundation for further exploration of the synergistic regulation of growth by GA and auxin in Moso bamboo.

Single-cell transcriptome atlas reveals spatiotemporal developmental trajectories in the basal roots of moso bamboo (Phyllostachys edulis)

Roots are essential for plant growth and development. Bamboo is a large Poaceae perennial with 1642 species worldwide. However, little is known about the transcriptional atlas that underpins root cell-type differentiation. Here, we set up a modified protocol for protoplast preparation and report single-cell transcriptomes of 14 279 filtered single cells derived from the basal root tips of moso bamboo. We identified four cell types and defined new cell-type-specific marker genes for the basal root. We reconstructed the developmental trajectories of the root cap, epidermis, and ground tissues and elucidated critical factors regulating cell fate determination. According to in situ hybridization and pseudotime trajectory analysis, the root cap and epidermis originated from a common initial cell lineage, revealing the particularity of bamboo basal root development. We further identified key regulatory factors for the differentiation of these cells and indicated divergent root developmental pathways between moso bamboo and rice. Additionally, PheWOX13a and PheWOX13b ectopically expressed in Arabidopsis inhibited primary root and lateral root growth and regulated the growth and development of the root cap, which was different from WOX13 orthologs in Arabidopsis. Taken together, our results offer an important resource for investigating the mechanism of root cell differentiation and root system architecture in perennial woody species of Bambusoideae.

Phytohormone Crosstalk of Cytokinin Biosynthesis and Signaling Family Genes in Moso Bamboo (Phyllostachys edulis)

Cytokinin is widely involved in the regulation of plant growth, but its pathway-related genes have not been reported in Moso bamboo. In this study, a total of 129 candidate sequences were identified by bioinformatic methods. These included 15 IPT family genes, 19 LOG family genes, 22 HK family genes, 11 HP family genes and 62 RR family genes. Phylogenetic analysis revealed that the cytokinin pathway was closely related to rice, and evolutionary pattern analysis found that most of the genes have syntenic relationship with rice-related genes. The Moso bamboo cytokinin pathway was evolutionarily conservative and mainly underwent purifying selection, and that gene family expansion was mainly due to whole-gene duplication events. Analysis of transcriptome data revealed a tissue-specific expression pattern of Moso bamboo cytokinin family genes, with auxin and gibberellin response patterns. Analysis of co-expression patterns at the developmental stages of Moso bamboo shoots revealed the existence of a phytohormone co-expression pattern centered on cytokinin signaling genes. The auxin signaling factor PheARF52 was identified by yeast one-hybrid assay as regulating the PheRR3 gene through a P-box element in the PheRR3 promoter region. Auxin and cytokinin signaling crosstalk to regulate Moso bamboo growth. Overall, we systematically identified and analyzed key gene families of the cytokinin pathway in Moso bamboo and obtained key factors for auxin and cytokinin crosstalk, laying the foundation for the study of hormone regulation in Moso bamboo.

Plasticity in the Morphology of Growing Bamboo: A Bayesian Analysis of Exogenous Treatment Effects on Plant Height, Internode Length, and Internode Numbers

Sucrose (Suc) and gibberellin (GA) can promote the elongation of certain internodes in bamboo. However, there is a lack of field studies to support these findings and no evidence concerning how Suc and GA promote the plant height of bamboo by regulating the internode elongation and number. We investigated the plant height, the length of each internode, and the total number of internodes of Moso bamboo (Phyllostachys edulis) under exogenous Suc, GA, and control group (CTRL) treatments in the field and analyzed how Suc and GA affected the height of Moso bamboo by promoting the internode length and number. The lengths of the 10th-50th internodes were significantly increased under the exogenous Suc and GA treatments, and the number of internodes was significantly increased by the exogenous Suc treatment. The increased effect of Suc and GA exogenous treatment on the proportion of longer internodes showed a weakening trend near the plant height of 15-16 m compared with the CTRL, suggesting that these exogenous treatments may be more effective in regions where bamboo growth is suboptimal. This study demonstrated that both the exogenous Suc and GA treatments could promote internode elongation of Moso bamboo in the field. The exogenous GA treatment had a stronger effect on internode elongation, and the exogenous Suc treatment had a stronger effect on increasing the internode numbers. The increase in plant height by the exogenous Suc and GA treatments was promoted by the co-elongation of most internodes or the increase in the proportion of longer internodes.

Transcriptomic Complexity of Culm Growth and Development in Different Types of Moso Bamboo

Moso bamboo is capable of both sexual and asexual reproduction during natural growth, resulting in four distinct types of culms: the bamboo shoot-culm, the seedling stem, the leptomorph rhizome, and a long-ignored culm-the outward-rhizome. Sometimes, when the outward rhizomes break through the soil, they continue to grow longitudinally and develop into a new individual. However, the roles of alternative transcription start sites (aTSS) or termination sites (aTTS) as well as alternative splicing (AS) have not been comprehensively studied for their development. To re-annotate the moso bamboo genome and identify genome-wide aTSS, aTTS, and AS in growing culms, we utilized single-molecule long-read sequencing technology. In total, 169,433 non-redundant isoforms and 14,840 new gene loci were identified. Among 1311 lncRNAs, most of which showed a positive correlation with their target mRNAs, one-third of these IncRNAs were preferentially expressed in winter bamboo shoots. In addition, the predominant AS type observed in moso bamboo was intron retention, while aTSS and aTTS events occurred more frequently than AS. Notably, most genes with AS events were also accompanied by aTSS and aTTS events. Outward rhizome growth in moso bamboo was associated with a significant increase in intron retention, possibly due to changes in the growth environment. As different types of moso bamboo culms grow and develop, a significant number of isoforms undergo changes in their conserved domains due to the regulation of aTSS, aTTS, and AS. As a result, these isoforms may play different roles than their original functions. These isoforms then performed different functions from their original roles, contributing to the transcriptomic complexity of moso bamboo. Overall, this study provided a comprehensive overview of the transcriptomic changes underlying different types of moso bamboo culm growth and development.

Shoot Nutrition and Flavor Variation in Two Phyllostachys Species: Does the Quality of Edible Bamboo Shoot Diaphragm and Flesh Differ?

For their quality evaluation, it is essential to determine both bamboo shoot nutrition and palatability, which will have a decisive effect on their economic value and market potential. However, differences in shoot nutrition and flavor variation among bamboo species, positions, and components have not been scientifically validated. This study assessed nutritional and flavor differences in two components (i.e., shoot flesh (BSF) and diaphragm (BSD)) of two Phyllostachys species (i.e., Phyllostachys edulis and Phyllostachys violascens) and analyzed any positional variation. Results showed that BSF protein, starch, fat, and vitamin C contents were comparatively higher. Nutrient compounds in the upper shoot segment of Ph. edulis were higher and contained less cellulose and lignin. However, both species’ BSD total acid, oxalic acid, and tannin contents were comparable. BSD soluble sugar and sugar:acid ratio were higher than upper BSD total amino acid, four key amino acids (i.e., essential amino acid, bitter amino acid, umami amino acid, and sweet amino acid flavor compounds), and associated ratios were all higher than BSF while also being rich in amino acids. The content and proportion of BSF essential and bitter amino acid flavor compounds in Ph. edulis were high relative to Ph. violascens. Conversely, the content and proportion of BSD umami and sweet amino acid flavor compounds were comparable to that of Ph. edulis. Our results showed that bamboo shoot quality was affected by flavor compound differences and that interspecific and shoot components interact. This study offers a new perspective to determine the formative mechanisms involved in bamboo shoot quality while providing a basis for their different usages.

Development of an efficient expression system with large cargo capacity for interrogation of gene function in bamboo based on bamboo mosaic virus

Bamboo is one of the fastest growing plants among monocotyledonous species and is grown extensively in subtropical regions. Although bamboo has high economic value and produces much biomass quickly, gene functional research is hindered by the low efficiency of genetic transformation in this species. We therefore explored the potential of a bamboo mosaic virus (BaMV)-mediated expression system to investigate genotype-phenotype associations. We determined that the sites between the triple gene block proteins (TGBps) and the coat protein (CP) of BaMV are the most efficient insertion sites for the expression of exogenous genes in both monopodial and sympodial bamboo species. Moreover, we validated this system by individually overexpressing the two endogenous genes ACE1 and DEC1, which resulted in the promotion and suppression of internode elongation, respectively. In particular, this system was able to drive the expression of three 2A-linked betalain biosynthesis genes (more than 4 kb in length) to produce betalain, indicating that it has high cargo capacity and may provide the prerequisite basis for the development of a DNA-free bamboo genome editing platform in the future. Since BaMV can infect multiple bamboo species, we anticipate that the system described in this study will greatly contribute to gene function research and further promote the molecular breeding of bamboo.

Comprehensive profiling of epigenetic modifications in fast-growing Moso bamboo shoots

The fast growth of Moso bamboo (Phyllostachys edulis) shoots is caused by the rapid elongation of each internode. However, the key underlying cellular processes and epigenetic mechanisms remain largely unexplored. We used microscopy and multi-omics approaches to investigate two regions (bottom and middle) of the 18th internode from shoots of two different heights (2 and 4 m). We observed that internode cells become longer, and that lignin biosynthesis and glycosyltransferase family 43 (GT43) genes are substantially upregulated with shoot height. Nanopore direct RNA sequencing (DRS) revealed a higher N6-methyladenine (m6A) modification rate in 2-m shoots than in 4-m shoots. In addition, different specific m6A modification sites were enriched at different growth stages. Global DNA methylation profiling indicated that DNA methylation levels are higher in 4-m shoots than in 2-m shoots. We also detected shorter poly(A) tail lengths (PALs) in 4-m shoots compared with 2-m shoots. Genes showing differential PAL were mainly enriched in the functional terms of protein translation and vesicle fusion. An association analysis between PALs and DNA methylation strongly suggested that gene body CG methylation levels are positively associated with PAL. This study provides valuable information to better understand post-transcriptional regulations responsible for fast-growing shoots in Moso bamboo.

Photosynthesis, Phytohormone Signaling and Sugar Catabolism in the Culm Sheaths of Phyllostachys edulis

Culm sheaths play an important role in supporting and protecting bamboo shoots during the growth and development period. The physiological and molecular functions of bamboo sheaths during the growth of bamboo shoots remain unclear. In this study, we investigated the morphological anatomy of culm sheaths, photosynthesis in sheath blades, storage and distribution of sugars, and the transcriptome of the sheath. Respiration in the base of the culm sheath was higher than that in the sheath blades; chloroplasts matured with the development of the sheath blades, the fluorescence efficiency Fv/Fm value increased from 0.3 to 0.82; and sucrose and hexose accumulated in the sheath blade and the culm sheath. The sucrose, glucose, and fructose contents of the middle sheath blades were 10.66, 5.73, and 8.84 mg/g FW, respectively. Starches accumulated in parenchymal cells close to vascular bundles. Genes related to the plant hormone signaling pathway and sugar catabolism were highly expressed in the culm sheath base. These findings provide a research basis for further understanding the possible role of bamboo sheaths in the growth and development of bamboo shoots.

PhePLATZ1, a PLATZ transcription factor in moso bamboo (Phyllostachys edulis), improves drought resistance of transgenic Arabidopsis thaliana

Drought is one of the most serious environmental stresses. Plant AT-rich sequence and zinc-binding (PLATZ) proteins perform indispensable functions to regulate plant growth and development and to respond to environmental stress. In this present study, we identified PhePLATZ1 in moso bamboo and found that its expression was up-regulated in response to 20% PEG-6000 and abscisic acid (ABA) treatments. Next, transgenic PhePLATZ1-overexpressing Arabidopsis lines were generated. Overexpression of PhePLATZ1 improved drought stress resistance of transgenic plants by mediating osmotic regulation, enhancing water retention capacity and reducing membrane and oxidative damage. These findings were corroborated by analysing physiological indicators including chlorophyll, relative water content, leaf water loss rate, electrolyte leakage, H₂O₂, proline, malondialdehyde content and the enzyme activities of peroxidase and catalase. Subsequent seed germination and seedling root length experiments that included exposure to exogenous ABA treatments showed that ABA sensitivity decreased in transgenic plants relative to wild-type plants. Moreover, transgenic PhePLATZ1-overexpressing plants promoted stomatal closure in response to ABA treatment, suggesting that PhePLATZ1 might play a positive regulatory role in the drought resistance of plants via the ABA signaling pathway. In addition, the transgenic PhePLATZ1-OE plants showed altered expression of some stress-related genes when grown under drought conditions. Taken together, these findings improve our understanding of the drought response of moso bamboo and provide a key candidate gene for the molecular breeding of this species for drought tolerance.

Full-length transcriptome-referenced analysis reveals crucial roles of hormone and wounding during induction of aerial bulbils in lily

Aerial bulbils are important vegetative reproductive organs in Lilium. They are often perpetually dormant in most Lilium species, and little is known about the induction of these vegetative structures. The world-famous Oriental hybrid lily cultivar 'Sorbonne', which blooms naturally devoid of aerial bulbils, is known for its lovely appearance and sweet fragrance. We found that decapitation stimulated the outgrowth of aerial bulbils at lower stems (LSs) and then application of low and high concentrations of IAA promoted aerial bulbils emergence around the wound at upper stems (USs) of 'Sorbonne'. However, the genetic basis of aerial bulbil induction is still unclear. Herein, 'Sorbonne' transcriptome has been sequenced for the first time using the combination of third-generation long-read and next-generation short-read technology. A total of 46,557 high-quality non-redundant full-length transcripts were generated. Transcriptomic profiling was performed on seven tissues and stems with treatments of decapitation and application of low and high concentrations of IAA, respectively. Functional annotation of 1918 DEGs within stem samples of different treatments showed that hormone signaling, sugar metabolism and wound-induced genes were crucial to bulbils outgrowth. The expression pattern of auxin-, shoot branching hormone-, plant defense hormone- and wound-inducing-related genes indicated their crucial roles in bulbil induction. Then we established five hormone- and wounding-regulated co-expression modules and identified some candidate transcriptional factors, such as MYB, bZIP, and bHLH, that may function in inducing bulbils. High connectivity was observed among hormone signaling genes, wound-induced genes, and some transcriptional factors, suggesting wound- and hormone-invoked signals exhibit extensive cross-talk and regulate bulbil initiation-associated genes via multilayered regulatory cascades. We propose that the induction of aerial bulbils at LSs after decapitation can be explained as the release of apical dominance. In contrast, the induction of aerial bulbils at the cut surface of USs after IAA application occurs via a process similar to callus formation. This study provides abundant candidate genes that will deepen our understanding of the regulation of bulbil outgrowth, paving the way for further molecular breeding of lily.

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.

PheGRF4e initiated auxin signaling during moso bamboo shoot development

BACKGROUND

As a ubiquitous acid-regulating protein family in eukaryotes, general regulatory factors (GRFs) are active in various life activities of plants. However, detailed investigations of the GRFs gene family in moso bamboo are scarce.

METHODS AND RESULTS

Genome-wide characteristics of the GRF gene family in moso bamboo were analyzed using the moso bamboo genome. GRF phylogeny, gene structure, conserved domains, cis-element promoters, and gene expression were systematically analyzed. A total of 20 GRF gene family members were identified in the moso bamboo genome. These genes were divided into ε and non-ε groups. qRT-PCR (real-time quantitative reverse transcription polymerase chain reaction) showed that PheGRF genes responded to auxin and gibberellin treatment. To further study PheGRF gene functions, a yeast two-hybrid experiment was performed and verified by a bimolecular fluorescence complementation experiment. The results showed that PheGRF4e could interact with PheIAA30 (auxin/indole-3-acetic acid, an Aux/IAA family gene), and both were found to act mainly on the root tip meristem and vascular bundle cells of developing shoots by in situ hybridization assay.

CONCLUSIONS

This study revealed that PheGRF genes were involved in hormone response during moso bamboo shoot development, and the possible regulatory functions of PheGRF genes were enriched by the fact that PheGRF4e initiated auxin signaling by binding to PheIAA30.

New Insights Into the Local Auxin Biosynthesis and Its Effects on the Rapid Growth of Moso Bamboo (Phyllostachys edulis)

Auxin plays a crucial regulatory role in higher plants, but systematic studies on the location of auxin local biosynthesis are rare in bamboo and other graminaceous plants. We studied moso bamboo (Phyllostachys edulis), which can grow up to 1 m/day and serves as a reference species for bamboo and other fast-growing species. We selected young tissues such as root tips, shoot tips, young culm sheaths, sheath blades, and internode divisions for local auxin biosynthesis site analysis. IAA immunofluorescence localization revealed that auxin was similarly distributed in different stages of 50-cm and 300-cm bamboo shoots. Shoot tips had the highest auxin content, and it may be the main site of auxin biosynthesis in the early stage of rapid growth. A total of 22 key genes in the YUCCA family for auxin biosynthesis were identified by genome-wide identification, and these had obvious tissue-specific and spatio-temporal expression patterns. In situ hybridization analysis revealed that the localization of YUCCA genes was highly consistent with the distribution of auxin. Six major auxin synthesis genes, PheYUC3-1, PheYUC6-1, PheYUC6-3, PheYUC9-1, PheYUC9-2, and PheYUC7-3, were obtained that may have regulatory roles in auxin accumulation during moso bamboo growth. Culm sheaths were found to serve as the main local sites of auxin biosynthesis and the auxin required for internode elongation may be achieved mainly by auxin transport.

Total and Mitochondrial Transcriptomic and Proteomic Insights into Regulation of Bioenergetic Processes for Shoot Fast-Growth Initiation in Moso Bamboo

As a fast-growing, woody grass plant, Moso bamboo (Phyllostachys edulis) can supply edible shoots, building materials, fibrous raw material, raw materials for crafts and furniture and so on within a relatively short time. Rapid growth of Moso bamboo occurs after the young bamboo shoots are covered with a shell and emerge from the ground. However, the molecular reactions of bioenergetic processes essential for fast growth remain undefined. Herein, total and mitochondrial transcriptomes and proteomes were compared between spring and winter shoots. Numerous key genes and proteins responsible for energy metabolism were significantly upregulated in spring shoots, including those involved in starch and sucrose catabolism, glycolysis, the pentose phosphate pathway, the tricarboxylic acid cycle and oxidative phosphorylation. Accordingly, significant decreases in starch and soluble sugar, higher ATP content and higher rates of respiration and glycolysis were identified in spring shoots. Further, the upregulated genes and proteins related to mitochondrial fission significantly increased the number of mitochondria, indirectly promoting intracellular energy metabolism. Moreover, enhanced alternate-oxidase and uncoupled-protein pathways in winter shoots showed that an efficient energy-dissipating system was important for winter shoots to adapt to the low-temperature environment. Heterologous expression of PeAOX1b in Arabidopsis significantly affected seedling growth and enhanced cold-stress tolerance. Overall, this study highlights the power of comparing total and mitochondrial omics and integrating physiochemical data to understand how bamboo initiates fast growth through modulating bioenergetic processes.

Transcriptome and miRNAome analysis reveals components regulating tissue differentiation of bamboo shoots

Primary thickening determines bamboo yield and wood property. However, little is known about the regulatory networks involved in this process. This study identified a total of 58,652 genes and 150 miRNAs via transcriptome and small RNA sequencing using the underground thickening shoot samples of wild-type (WT) Moso bamboo (Phyllostachys edulis) and a thick wall (TW) variant (P. edulis "Pachyloen") at five developmental stages (WTS1/TWS1-WTS5/TWS5). A total of 14,029 (65.17%) differentially expressed genes and 68 (45.33%) differentially expressed miRNAs were identified from the WT, TW, and WTTW groups. The first two groups were composed of four pairwise combinations, each between two successive stages (WTS2/TWS2_versus_WTS1/TWS1, WTS3/TWS3_versus_WTS2/TWS2, WTS4/TWS4_versus_WTS3/TWS3, and WTS5/TWS5_versus_WTS4/TWS4), and the WTTW group was composed of five combinations, each between two relative stages (TWS1-5_versus_WTS1-5). Additionally, among the phytohormones, zeatin showed more remarkable changes in concentrations than indole-3-acetic acid, gibberellic acid, and abscisic acid throughout the five stages in the WT and the TW groups. Moreover, 125 cleavage sites were identified for 387 miRNA-mRNA pairs via degradome sequencing (P < 0.05). The dual-luciferase reporter assay confirmed that 13 miRNAs bound to 12 targets. Fluorescence in situ hybridization localized miR166 and miR160 in the shoot apical meristem and the procambium of Moso bamboo shoots at the S1 stage. Thus, primary thickening is a complex process regulated by miRNA-gene-phytohormone networks, and the miRNAome and transcriptome dynamics regulate phenotypic plasticity. These findings provide insights into the molecular mechanisms underlying wood formation and properties and propose targets for bamboo breeding.

Cellular and molecular characterizations of the irregular internode division zone formation of a slow-growing bamboo variant

The key molecular mechanisms underlying the sectionalized growth within bamboo or other grass internodes remain largely unknown. Here, we genetically and morphologically compared the culm and rhizome internode division zones (DZs) of a slow-growing bamboo variant (sgv) having dwarf internodes, with those of the corresponding wild type (WT). Histological analysis discovers that the sgv has an irregular internode DZ. However, the shoot apical meristems in height, width, outside shape, cell number and cell width of the sgv and the WT were all similar. The DZ irregularities first appeared post apical meristem development, in 1-mm sgv rhizome internodes. Thus, the sgv is a DZ irregularity bamboo variant, which has been first reported in bamboo according to our investigation. Transcriptome sequencing analysis finds that a number of cell wall biogenesis and cell division-related genes are dramatically downregulated in the sgv DZ. Interestingly, both transcriptomic and brassinosteroid (BR) contents detection, as well as quantitative real-time PCR analyses show that these irregularities have resulted from the BR signaling pathway defects. Brassinosteroid defect might also cause the erect leaves and branches as well as the irregular epidermis of the sgv. These results suggest that BR signaling pathway plays critical roles in bamboo internode DZ and leaf development from a mutant perspective and also explain the upstream mechanisms causing the dwarf internode of the sgv bamboo.

Hormone and carbohydrate metabolism associated genes play important roles in rhizome bud full-year germination of Cephalostachyum pingbianense

Cephalostachyum pingbianense is the only woody bamboo species that can produce bamboo shoots in four seasons under natural conditions. So far, the regulatory mechanism of shoot bud differentiation and development is unknown. In the present study, indole-3-acetic acid (IAA), zeatin riboside (ZR), gibberellin A3 (GA₃ ) and abscisic acid (ABA) contents determination, RNA sequencing and differentially expressed gene analysis were performed on dormant rhizome bud (DR), growing rhizome bud (GR), and germinative bud (GB) in each season. The results showed that the contents of IAA and ZR increased while ABA content decreased, and GA₃ content was stable during bud transition from dormancy to germination in each season. Moreover, rhizome bud germination was cooperatively regulated by multiple pathways such as carbohydrate metabolism, hormone signal transduction, cell wall biogenesis, temperature response, and water transport. The inferred hub genes among these candidates were identified by protein-protein interaction network analyses, most of which were involved in hormone and carbohydrate metabolism, such as HK and BGLU4 in spring, IDH and GH3 in winter, GPI and talA/talB in summer and autumn. It is speculated that dynamic phytohormone changes and differential expression of these genes promote the release of rhizome bud dormancy and contribute to the phenological characteristics of full-year shooting. Moreover, the rhizome buds of C. pingbianense may not suffer from ecodormancy in winter. These findings would help accumulate knowledge on shooting mechanisms in woody bamboos and provide a physiological insight into germplasm conservation and forest management of C. pingbianense.

Allele-aware chromosome-scale assembly of the allopolyploid genome of hexaploid Ma bamboo (Dendrocalamus latiflorus Munro)

Dendrocalamus latiflorus Munro is a woody clumping bamboo with rapid shoot growth. Both genetic transformation and clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) gene editing techniques are available for D. latiflorus, enabling reverse genetic approaches. Thus, D. latiflorus has the potential to be a model bamboo species. However, the genome sequence of D. latiflorus has remained unreported due to its polyploidy and large genome size. Here, we sequenced the D. latiflorus genome and assembled it into three allele-aware subgenomes (AABBCC), representing the largest genome of a major bamboo species. We assembled 70 allelic chromosomes (2, 737 Mb) for hexaploid D. latiflorus using both single-molecule sequencing from the Pacific Biosciences (PacBio) Sequel platform and chromosome conformation capture sequencing (Hi-C). Repetitive sequences comprised 52.65% of the D. latiflorus genome. We annotated 135 231 protein-coding genes in the genome based on transcriptomes from eight different tissues. Transcriptome sequencing using RNA-Seq and PacBio single-molecule real-time long-read isoform sequencing revealed highly differential alternative splicing (AS) between non-abortive and abortive shoots, suggesting that AS regulates the abortion rate of bamboo shoots. This high-quality hexaploid genome and comprehensive strand-specific transcriptome datasets for this Poaceae family member will pave the way for bamboo research using D. latiflorus as a model species.

Anatomical Characteristics and Variation Mechanisms on the Thick-Walled and Dwarfed Culm of Shidu Bamboo (Phyllostachys nidularia f. farcta)

Stable culm variants are valuable and important material for the study of culm development in bamboo plants. However, to date, there are few reports on the mechanism of variation of these bamboo variants. Phyllostachys nidularia f. farcta (Shidu bamboo) is a bamboo variant with stable phenotypes such as a dwarf culm with a thickened wall. In this study, we systematically investigated the cytological characteristics and underlying mechanism of morphological variation in culms of this variant using anatomical, mathematical statistical, physiological, and genomic methods. The anatomical observation and statistical results showed that the lateral increase of ground tissue in the inner layer of culm wall and the enlargement of vascular bundles are the anatomical essence of the wall thickening of Shidu bamboo; the limited elongation of fiber cells and the decrease in the number of parenchyma cells longitudinally are probably the main causes of the shortening of its internodes. A number of genes involved in the gibberellin synthesis pathway and in the synthesis of cell wall components are differentially expressed between the variant and its prototype, Ph. nidularia, and may play an important role in determining the phenotype of internode shortening in Shidu bamboo. The decrease in gibberellin content and the content of the major chemical components of the cell wall of Shidu bamboo confirmed the results of the above transcriptome. In addition, the variation in culm morphology in Shidu bamboo had little effect on the volume of the culm wall of individual internodes, suggesting that the decrease in the total number of internodes and the decrease in dry matter content (lignin, cellulose, etc.) may be the main factor for the sharp decline in culm biomass of Shidu bamboo.

The Effect of Guttation on the Growth of Bamboo Shoots

Guttation is the process of exudating droplets from the tips, edges, and adaxial and abaxial surfaces of the undamaged leaves. Guttation is a natural and spontaneous biological phenomenon that occurs in a wide variety of plants. Despite its generally positive effect on plant growth, many aspects of this cryptic process are unknown. In this study, the guttation phenomenon characteristic of bamboo shoots and the anatomical feature of these and culm sheaths were systematically observed. In addition, the water transport pathway and the compounds in guttation droplets of bamboo shoots were analyzed, and the effect of bamboo sheaths’ guttation on the growth of bamboo shoots was assessed. The results revealed that bamboo shoots began to exudate liquid in the evening through to the next morning, during which period the volume of guttation liquid gradually increases and then decreases before sunrise. Many vascular bundles are in bamboo shoots and culm sheaths to facilitate this water transport. The exudate liquid contains organic acids, sugars, and hormones, among other compounds. Our findings suggest that the regular guttation of the sheath blade is crucial to maintain the normal growth of bamboo shoots.

Association among starch storage, metabolism, related genes and growth of Moso bamboo (Phyllostachys heterocycla) shoots

BACKGROUND

Both underground rhizomes/buds and above-ground Moso bamboo (Phyllostachys heterocycla) shoots/culms/branches are connected together into a close inter-connecting system in which nutrients are transported and shared among each organ. However, the starch storage and utilization mechanisms during bamboo shoot growth remain unclear. This study aimed to reveal in which organs starch was stored, how carbohydrates were transformed among each organ, and how the expression of key genes was regulated during bamboo shoot growth and developmental stages which should lay a foundation for developing new theoretical techniques for bamboo cultivation.

RESULTS

Based on changes of the NSC content, starch metabolism-related enzyme activity and gene expression from S0 to S3, we observed that starch grains were mainly elliptical in shape and proliferated through budding and constriction. Content of both soluble sugar and starch in bamboo shoot peaked at S0, in which the former decreased gradually, and the latter initially decreased and then increased as shoots grew. Starch synthesis-related enzymes (AGPase, GBSS and SBE) and starch hydrolase (α-amylase and β-amylase) activities exhibited the same dynamic change patterns as those of the starch content. From S0 to S3, the activity of starch synthesis-related enzyme and starch amylase in bamboo rhizome was significantly higher than that in bamboo shoot, while the NSC content in rhizomes was obviously lower than that in bamboo shoots. It was revealed by the comparative transcriptome analysis that the expression of starch synthesis-related enzyme-encoding genes were increased at S0, but reduced thereafter, with almost the same dynamic change tendency as the starch content and metabolism-related enzymes, especially during S0 and S1. It was revealed by the gene interaction analysis that AGPase and SBE were core genes for the starch and sucrose metabolism pathway.

CONCLUSIONS

Bamboo shoots were the main organ in which starch was stored, while bamboo rhizome should be mainly functioned as a carbohydrate transportation channel and the second carbohydrate sink. Starch metabolism-related genes were expressed at the transcriptional level during underground growth, but at the post-transcriptional level during above-ground growth. It may be possible to enhance edible bamboo shoot quality for an alternative starch source through genetic engineering.

Genomic insights into the fast growth of paulownias and the formation of Paulownia witches' broom

Paulownias are among the fastest growing trees in the world, but they often suffer tremendous loss of wood production due to infection by Paulownia witches' broom (PaWB) phytoplasmas. In this study, we have sequenced and assembled a high-quality nuclear genome of Paulownia fortunei, a commonly cultivated paulownia species. The assembled genome of P. fortunei is 511.6 Mb in size, with 93.2% of its sequences anchored to 20 pseudo-chromosomes, and it contains 31 985 protein-coding genes. Phylogenomic analyses show that the family Paulowniaceae is sister to a clade composed of Phrymaceae and Orobanchaceae. Higher photosynthetic efficiency is achieved by integrating C3 photosynthesis and the crassulacean acid metabolism pathway, which may contribute to the extremely fast growth habit of paulownia trees. Comparative transcriptome analyses reveal modules related to cambial growth and development, photosynthesis, and defense responses. Additional genome sequencing of PaWB phytoplasma, combined with functional analyses, indicates that the effector PaWB-SAP54 interacts directly with Paulownia PfSPLa, which in turn causes the degradation of PfSPLa by the ubiquitin-mediated pathway and leads to the formation of witches' broom. Taken together, these results provide significant insights into the biology of paulownias and the regulatory mechanism for the formation of PaWB.

New Genes Interacted with Recent Whole Genome Duplicates in the Fast Stem Growth of Bamboos

As drivers of evolutionary innovations, new genes allow organisms to explore new niches. However, clear examples of this process remain scarce. Bamboos, the unique grass lineage diversifying into the forest, have evolved with a key innovation of fast growth of woody stem, reaching up to 1 m/day. Here, we identify 1,622 bamboo-specific orphan genes that appeared in recent 46 million years, and 19 of them evolved from noncoding ancestral sequences with entire de novo origination process reconstructed. The new genes evolved gradually in exon−intron structure, protein length, expression specificity, and evolutionary constraint. These new genes, whether or not from de novo origination, are dominantly expressed in the rapidly developing shoots, and make transcriptomes of shoots the youngest among various bamboo tissues, rather than reproductive tissue in other plants. Additionally, the particularity of bamboo shoots has also been shaped by recent whole-genome duplicates (WGDs), which evolved divergent expression patterns from ancestral states. New genes and WGDs have been evolutionarily recruited into coexpression networks to underline fast-growing trait of bamboo shoot. Our study highlights the importance of interactions between new genes and genome duplicates in generating morphological innovation.

Functional analyses unveil the involvement of moso bamboo (Phyllostachys edulis) group I and II NIN-LIKE PROTEINS in nitrate signaling regulation

For rapid growth, moso bamboo (Phyllostachys edulis) requires large amounts of nutrients. Nitrate is an indispensable molecular signal to regulate nitrogen absorption and assimilation, which are regulated by group III NIN-LIKE PROTEINs (NLPs). However, no Phyllostachys edulis NLP (PeNLP) has been characterized. Here, eight PeNLPs were identified, which showed dynamic expression patterns in bamboo tissues. Nitrate did not affect PeNLP mRNA levels, and PeNLP1, -2, -5, -6, -7, and -8 successfully restored nitrate signaling in Arabidopsis atnlp7-1 protoplasts through recovering AtNiR and AtNRT2.1 expression. Four group I and II PeNLPs (PeNLP1, -2, -5, and -8) interacted with the nitrate-responsive cis-element of PeNiR. Moreover, nitrate triggered the nuclear retention of PeNLP8. PeNLP8 overexpression in Arabidopsis significantly increased the primary root length, lateral root number, leaf area, and dry and wet weight of the transgenic plants, and PeNLP8 expression rescued the root architectural defect phenotype of atnlp7-1 mutants. Interestingly, PeNLP8 overexpression dramatically reduced nitrate content but elevated total amino acid content in Arabidopsis. Overall, the present study unveiled the potential involvement of group I and II NLPs in nitrate signaling regulation and provided genetic resources for engineering plants with high nitrogen use efficiency.

Transcriptome analysis reveals key genes regulating signaling and metabolic pathways during the growth of moso bamboo (Phyllostachys edulis) shoots

Moso bamboo (Phyllostachys edulis), a high-value bamboo used to produce food (young shoots), building, and industrial goods. To explore key candidate genes regulating signal transduction and metabolic processes during the initiation of stem elongation in moso bamboo, a transcriptome analysis of the shoots during three successive early elongation stages was performed. From cluster and differential expression analyses, 2984 differentially expressed genes (DEGs) were selected for an enrichment analysis. The DEGs were significantly enriched in the plant hormone signal transduction, sugar and starch metabolism, and energy metabolism pathways. Consequently, the DEG expression patterns of these pathways were analyzed, and the plant endogenous hormone and carbon metabolite (including sucrose, total soluble sugar, and starch) contents for each growth stage, of the shoot, were determined. The cytokinin-signaling pathway was continuously active in the three successive elongation stages, in which several cytokinin-signaling genes played indispensable roles. Additionally, many key DEGs regulating sugar, starch metabolism, and energy conversion, which are actively involved in energy production and substrate synthesis during the continuous growth of the shoots, were found. In summary, our study lays a foundation for understanding the mechanisms of moso bamboo growth and provides useful gene resources for breeding through genetic engineering.

Genome-wide identification and functional characterization of the PheE2F/DP gene family in Moso bamboo

BACKGROUND

E2F/DP proteins have been shown to regulate genes implicated in cell cycle control and DNA repair. However, to date, research into the potential role of the Moso bamboo E2F/DP family has been limited.

RESULTS

Here, we identified 23 E2F/DPs in the Moso bamboo genome, including nine E2F genes, six DP genes, eight DEL genes and one gene with a partial E2F domain. An estimation of the divergence time of the paralogous gene pairs suggested that the E2F/DP family expansion primarily occurred through a whole-genome duplication event. A regulatory element and coexpression network analysis indicated that E2F/DP regulated the expression of cell cycle-related genes. A yeast two-hybrid assay and expression analysis based on transcriptome data and in situ hybridization indicated that the PheE2F-PheDP complex played important roles in winter Moso bamboo shoot growth. The qRT-PCR results showed that the PheE2F/DPs exhibited diverse expression patterns in response to drought and salt treatment and diurnal cycles.

CONCLUSION

Our findings provide novel insights into the Moso bamboo E2F/DP family and partial experimental evidence for further functional verification of the PheE2F/DPs.

Genome-wide identification and expression analysis of dirigent-jacalin genes from plant chimeric lectins in Moso bamboo (Phyllostachys edulis)

Dirigent-jacalin (D-J) genes belong to the plant chimeric lectin family, and play vital roles in plant growth and resistance to abiotic and biotic stresses. To explore the functions of the D-J family in the growth and development of Moso bamboo (Phyllostachys edulis), their physicochemical properties, phylogenetic relationships, gene and protein structures, and expression patterns were analyzed in detail. Four putative PeD-J genes were identified in the Moso bamboo genome, and microsynteny and phylogenetic analyses indicated that they represent a new branch in the evolution of plant lectins. PeD-J proteins were found to be composed of a dirigent domain and a jacalin-related lectin domain, each of which contained two different motifs. Multiple sequence alignment and homologous modeling analysis indicated that the three-dimensional structure of the PeD-J proteins was significantly different compared to other plant lectins, primarily due to the tandem dirigent and jacalin domains. We surveyed the upstream putative promoter regions of the PeD-Js and found that they mainly contained cis-acting elements related to hormone and abiotic stress response. An analysis of the expression patterns of root, leaf, rhizome and panicle revealed that four PeD-J genes were highly expressed in the panicle, indicating that they may be required during the formation and development of several different tissue types in Moso bamboo. Moreover, PeD-J genes were shown to be involved in the rapid growth and development of bamboo shoots. Quantitative Real-time PCR (qRT PCR) assays further verified that D-J family genes were responsive to hormones and stresses. The results of this study will help to elucidate the biological functions of PeD-Js during bamboo growth, development and stress response.

Genome-wide identification, evolution and expression analysis of the aspartic protease gene family during rapid growth of moso bamboo (Phyllostachys edulis) shoots

BACKGROUND

Aspartic proteases (APs) are a class of aspartic peptidases belonging to nine proteolytic enzyme families whose members are widely distributed in biological organisms. APs play essential functions during plant development and environmental adaptation. However, there are few reports about APs in fast-growing moso bamboo.

RESULT

In this study, we identified a total of 129 AP proteins (PhAPs) encoded by the moso bamboo genome. Phylogenetic and gene structure analyses showed that these 129 PhAPs could be divided into three categories (categories A, B and C). The PhAP gene family in moso bamboo may have undergone gene expansion, especially the members of categories A and B, although homologs of some members in category C have been lost. The chromosomal location of PhAPs suggested that segmental and tandem duplication events were critical for PhAP gene expansion. Promoter analysis revealed that PhAPs in moso bamboo may be involved in plant development and responses to environmental stress. Furthermore, PhAPs showed tissue-specific expression patterns and may play important roles in rapid growth, including programmed cell death, cell division and elongation, by integrating environmental signals such as light and gibberellin signals.

CONCLUSION

Comprehensive analysis of the AP gene family in moso bamboo suggests that PhAPs have experienced gene expansion that is distinct from that in rice and may play an important role in moso bamboo organ development and rapid growth. Our results provide a direction and lay a foundation for further analysis of plant AP genes to clarify their function during rapid growth.

PeSNAC-1 a NAC transcription factor from moso bamboo (Phyllostachys edulis) confers tolerance to salinity and drought stress in transgenic rice

NAC (NAM, AFAT and CUC) proteins play necessary roles in plant response to environmental stresses. However, the functional roles of NAC genes in moso bamboo (Phyllostachys edulis), an essential economic perennial woody bamboo species, are not well documented. In this study, we retrieved 152 PeNAC genes from the moso bamboo V2 genome, and PeSNAC-1 was isolated and functionally characterized. PeSNAC-1 was localized in the nucleus and had no transactivation activity in yeast. PeSNAC-1 extremely expressed in rhizome and young roots (0.1 and 0.5 cm) and was significantly induced by drought and salt treatments but repressed by abscisic acid (ABA), methyl jasmonate and high temperature (42 °C) in moso bamboo. Under water shortage and salinity conditions, survival ratios, Fv/Fm values, physiological indexes such as activities of superoxide dismutase, peroxidase and catalase and contents of malondialdehyde, H2O2 and proline were significantly higher in transgenic rice than the wild type, which suggests enhanced tolerance to drought and salt stress in PeSANC-1 overexpressed plants. Transcript levels of Na+/H+ antiporter and Na+ transporter genes (OsSOS1, OsNHX1 and OsHKT1;5), ABA signaling and biosynthesis genes (OsABI2, OsRAB16, OsPP2C68, OsLEA3-1, OsLEA3, OsNCED3, OsNCED4 and OsNCED5) and ABA-independent genes (OsDREB1A, OsDREB1B and OsDREB2A) were substantially higher in transgenic as compared with the wild type. Moreover, protein interaction analysis revealed that PeSNAC-1 could interact with stress responsive PeSNAC-2/4 and PeNAP-1/4/5 in both yeast and plant cells, which indicates a synergistic effect of those proteins in regulating the moso bamboo stress response. Our data demonstrate that PeSNAC-1 likely improved salt and drought stress tolerance via modulating gene regulation in both ABA-dependent and independent signaling pathways in transgenic rice. In addition, PeSNAC-1 functions as an important positive stress regulator in moso bamboo, participating in PeSNAC-1 and PeSNAC-2/4 or PeSNAC-1 and PeNAP-1/4/5 interaction networks.

Multi-omics analysis of cellular pathways involved in different rapid growth stages of moso bamboo

Moso bamboo (Phyllostachys edulis (Carriere) J. Houzeau) is a rapidly growing grass of industrial and ecological importance. However, the molecular mechanisms of its remarkable growth are not well understood. In this study, we investigated the early-stage growth of moso bamboo shoots and defined three different growth stages based on histological and biochemical analyses, namely, starting of cell division (SD), rapid division (RD) and rapid elongation (RE). Further analyses on potentially relevant cellular pathways in these growth stages using multi-omics approaches such as transcriptomics and proteomics revealed the involvement of multiple cellular pathways, including DNA replication, repair and ribosome biogenesis. A total of 8045 differentially expressed genes (DEGs) and 1053 differentially expressed proteins (DEPs) were identified in our analyses. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses of detected DEGs identified several key biological pathways such as phytohormone metabolism, signal transduction, cell wall development and carbohydrate metabolism. The comparative analysis of proteins displayed that a total of 213 DEPs corresponded with DEGs and 3 significant expression profiles that could be promoting the fast growth of bamboo internodes. Moreover, protein-protein interaction network prediction analysis is suggestive of the involvement of five major proteins of signal transduction, DNA synthesis and RNA transcription, and may act as key elements responsible for the rapid shoot growth. Our work exploits multi-omics and bioinformatic approaches to unfurl the complexity of molecular networks involved in the rapid growth of moso bamboo and opens up questions related to the interactions between the functions played by individual molecular pathway.

Transcriptome Reveals the Specificity of Phyllostachys edulis ‘Pachyloen’ Shoots at Different Developmental Stages

Phyllostachys edulis ‘Pachyloen’ can have a stalk wall thickness of up to 2.5 cm at a height of 1.3 m, which is 1.8 times that of normal Moso bamboo (Phyllostachys edulis); this serves as an excellent cultivar, comprising both wood and bamboo shoots. We collected bamboo shoot samples of Phyllostachys edulis ‘Pachyloen’ and Moso bamboo on a monthly basis from September to April and used transcriptome sequencing to explore the differences in their development. The results showed that there were 666–1839 Phyllostachys edulis ‘Pachyloen’-specific genes at different developmental stages enriched in 20 biological processes, 15 cellular components, 12 molecular functions, and 137 metabolic pathways, 52 of which were significant. Among these, 27 metabolic pathways such as tyrosine metabolism and their uniquely expressed genes were found to play important roles in the thickening of Phyllostachys edulis ‘Pachyloen’. This study provides insights into the mechanisms underlying the thickening of the culm wall of Phyllostachys edulis ‘Pachyloen’.

Slower development of lower canopy beans produces better coffee

The production of high-quality coffee is being challenged by changing climates in coffee-growing regions. The coffee beans from the upper and lower canopy at different development stages of the same plants were analyzed to investigate the impact of the microenvironment on gene expression and coffee quality. Compared with coffee beans from the upper canopy, lower canopy beans displayed more intense aroma with higher caffeine, trigonelline, and sucrose contents, associated with greater gene expression in the representative metabolic pathways. Global gene expression indicated a longer ripening in the lower canopy, resulting from higher expression of genes relating to growth inhibition and suppression of chlorophyll degradation during early bean ripening. Selection of genotypes or environments that enhance expression of the genes slowing bean development may produce higher quality coffee beans, allowing coffee production in a broader range of available future environments.

Genome-wide identification and characterization of UDP-glucose dehydrogenase family genes in moso bamboo and functional analysis of PeUGDH4 in hemicellulose synthesis

Uridine diphosphate glucose dehydrogenases (UGDHs) are critical for synthesizing many nucleotide sugars and help promote the carbohydrate metabolism related to cell wall synthesis. In plants, UGDHs are encoded by a small gene family. Genome-wide analyses of these genes have been conducted in Glycine max and Arabidopsis thaliana, however, the UGDH gene family has not been comprehensively and systematically investigated in moso bamboo (Phyllostachys edulis), which is a special woody grass monocotyledonous species. In this study, we identified nine putative PeUGDH genes. Furthermore, analysis of gene duplication events and divergences revealed that the expansion of the PeUGDH family was mainly due to segmental and tandem duplications approximately 4.76–83.16 million years ago. An examination of tissue-specific PeUGDH expression indicated that more than 77% of the genes were predominantly expressed in the stem. Based on relative expression levels among PeUGDH members in different tissues in moso bamboo, PeUGDH4 was selected for detailed analysis. The results of subcellular localization indicated that PeUGDH4-GFP fusion proteins was observed to be localized in the cytoplasm. The ectopic overexpression of PeUGDH4 in Arabidopsis significantly increased the contents of hemicellulose and soluble sugar, suggesting that PeUGDH4 acts as a key enzyme involved in bamboo cell wall synthesis.

Genome-Wide Identification and Characterization of Hexokinase Genes in Moso Bamboo (Phyllostachys edulis)

Plant hexokinases (HXKs) are a class of multifunctional proteins that not only act as the enzymes required for hexose phosphorylation but also serve as sugar sensors that repress the expression of some photosynthetic genes when internal glucose level increases and regulators of cell metabolism and some sugar-related signaling pathways independent on their catalytic actives. The HXKs have been studied in many plants; however, limited information is available on HXKs of moso bamboo (Phyllostachys edulis). In this study, we identified and characterized 12 hexokinase genes in moso bamboo. Phylogenetic analysis revealed that the moso bamboo hexokinases (PeHXKs) were classifiable into five subfamilies which represented the three types of hexokinases in plants. Gene structure and conserved motif analysis showed that the PeHXK genes contained diverse numbers of introns and exons and that the encoded proteins showed similar motif organization within each subfamily. Multiple sequence alignment revealed that the PeHXK proteins contained conserved domains, such as phosphate 1 (P1), phosphate 2 (P2), adenosine, and a sugar-binding domain. Evolutionary divergence analysis indicated that the PeHXK, OsHXK, and BdHXK families underwent negative selection and experienced a large-scale duplication event approximately 19-319 million years ago. Expression analysis of the PeHXK genes in the leaf, stem, root, and rhizome of moso bamboo seedlings indicated that the PeHXKs perform pivotal functions in the development of moso bamboo. A protein subcellular localization assay showed that PeHXK5a, PeHXK8, and PeHXK3b were predominantly localized in mitochondria, and PeHXK8 protein was also detected in the nucleus. The HXK activity of the PeHXK5a, PeHXK8, and PeHXK3b was verified by a functional complementation assay using the HXK-deficient triple-mutant yeast strain YSH7.4-3C (hxk1, hxk2, and glk1), and the results showed that the three PeHXKs had the plant HXK-specific enzyme traits. The present findings would provide a foundation for further functional analysis of the PeHXK gene family.

Identification and Evolution of the WUSCHEL-Related Homeobox Protein Family in Bambusoideae

Bamboos (Bambusoideae) are fast-growing species due to their rapid growth rate and ability to reproduce annually via cloned buds produced on the rhizome. WUSCHEL-related homeobox (WOX) genes have been reported to regulate shoot apical meristem organization, lateral organ formation, cambium and vascular proliferation, and so on, but have rarely been studied in bamboos. In this study, the WOXs of both herbaceous bamboo species (12 OlaWOXs and nine RguWOXs) and woody bamboo species (18 GanWOXs, 27 PheWOXs, and 26 BamWOXs) were identified and categorized into three clades based on their phylogenetic relationship-ancient, intermediate, or WUS clade. Polyploidy is the major driver of the expansion of the bamboo WOX family. Eight conserved domains, besides the homeodomain, were identified by comparatively analyzing the WOXs of dicot and monocot species. Intensive purifying selection pressure in the coding region of specific domains explained the functional similarity of WOXs between different species. For Bambusoideae WOXs, polyploidy is the major driver of the expansion of the WOX family. Stronger purifying selection was found in orthologous WOXs of Bambusoideae, especially for WOX4s and WOX5s, which are conserved not only at the translational levels, but also at the genome level. Several conserved cis-acting elements were discovered at similar position in the promoters of the orthologous WOXs. For example, AP2/ERF protein-binding elements and B3 protein-binding elements were found in the promoters of the bamboo WOX4, while MYB protein-binding elements and Dof protein-binding elements were found in the promoters of bamboo WOX5, and MADS protein-binding sites was found in the promoters of bamboo WUS, WOX3, and WOX9. These conserved positions may play an important role in regulating the expression of bamboo WOXs. Our work provides insight into the origin and evolution of bamboo WOXs, and will facilitate functional investigations of the clonal propagation of bamboos.

Genome-Wide Characterization and Gene Expression Analyses of GATA Transcription Factors in Moso Bamboo (Phyllostachys edulis)

Moso bamboo is well-known for its rapid-growth shoots and widespread rhizomes. However, the regulatory genes of these two processes are largely unexplored. GATA transcription factors regulate many developmental processes, but their roles in moso bamboo height control and rhizome development remains unexplored. Here, thirty-one bamboo GATA factors (PeGATAs) were identified, which are evolutionarily closer to rice than Arabidopsis, and their gene expression patterns were analyzed in bamboo development and phytohormone response with bioinformatics and molecular methods. Interestingly, PeGATAs could only be classified into three groups. Phytohormone responsive cis-elements were found in PeGATA promoters and the expression profiles showed that PeGATA genes might respond to gibberellin acid and abscisic acid but not to auxin at the transcriptional level. Furthermore, PeGATA genes have a tissue-specific expression pattern in bamboo rhizomes. Interestingly, most PeGATA genes were down-regulated during the rapid-growth of bamboo shoots. In addition, over-expressing one of the PeGATA genes, PeGATA26, significantly repressed the primary root length and plant height of transgenic Arabidopsis plants, which may be achieved by promoting the gibberellin acid turnover. Overall, our results provide insight into the function of GATA transcription factors in bamboo, and into genetic resources for engineering plant height.

Transcriptome profiling of postharvest shoots identifies PheNAP2- and PheNAP3-promoted shoot senescence

The juvenile shoots of Phyllostachys edulis have been used as a food source for thousands of years, and it is recognized as a potential source of nutraceuticals. However, its rapid senescence restricts bamboo production and consumption, and the underlying molecular mechanisms of rapid shoot senescence remain largely unclear. In the present study, transcriptome profiling was employed to investigate the molecular regulation of postharvest senescence in shoots, along with physiological assays and anatomical dissections. Results revealed a distinct shift in expression postharvest, specifically transitions from cellular division and differentiation to the relocation of nutrients and programmed cell death. A number of regulatory and signaling factors were induced during postharvest senescence. Moreover, transcription factors, including NAM, ATAF and CUC (NAC) transcription factors, basic helix-loop-helix transcription factors, basic region/leucine zipper transcription factors, MYB transcription factors and WRKY transcription factors, were critical for shoot postharvest senescence, of which NACs were the most abundant. PheNAP2 and PheNAP3 were induced in postharvest shoots and found to promote leaf senescence in Arabidopsis by inducing the expression of AtSAG12 and AtSAG113. PheNAP2 and PheNAP3 could both restore the stay-green Arabidopsis nap to the wild-type phenotype either under normal growth condition or under abscisic acid treatment. Collectively, these results suggest that PheNAPs may promote shoot senescence. These findings provide a systematic view of shoot senescence and will inform future studies on the underlying molecular mechanisms responsible for shoot degradation during storage.

Affinities of Terminal Inverted Repeats to DNA Binding Domain of Transposase Affect the Transposition Activity of Bamboo Ppmar2 Mariner-Like Element

Mariner-like elements (MLE) are a super-family of DNA transposons widespread in animal and plant genomes. Based on their transposition characteristics, such as random insertions and high-frequency heterogeneous transpositions, several MLEs have been developed to be used as tools in gene tagging and gene therapy. Two active MLEs, Ppmar1 and Ppmar2, have previously been identified in moso bamboo (Phyllostachys edulis). Both of these have a preferential insertion affinity to AT-rich region and their insertion sites are close to random in the host genome. In Ppmar2 element, we studied the affinities of terminal inverted repeats (TIRs) to DNA binding domain (DBD) and their influence on the transposition activity. We could identify two putative boxes in the TIRs which play a significant role in defining the TIR's affinities to the DBD. Seven mutated TIRs were constructed, differing in affinities based on similarities with those of other plant MLEs. Gel mobility shift assays showed that the TIR mutants with mutation sites G669A-C671A had significantly higher affinities than the mutants with mutation sites C657T-A660T. The high-affinity TIRs indicated that their transposition frequency was 1.5-2.0 times higher than that of the wild type TIRs in yeast transposition assays. The MLE mutants with low-affinity TIRs had relatively lower transposition frequency from that of wild types. We conclude that TIR affinity to DBD significantly affects the transposition activity of Ppmar2. The mutant MLEs highly active TIRs constructed in this study can be used as a tool for bamboo genetic studies.

Large Scale Profiling of Protein Isoforms Using Label-Free Quantitative Proteomics Revealed the Regulation of Nonsense-Mediated Decay in Moso Bamboo (Phyllostachys edulis)

Moso bamboo is an important forest species with a variety of ecological, economic, and cultural values. However, the gene annotation information of moso bamboo is only based on the transcriptome sequencing, lacking the evidence of proteome. The lignification and fiber in moso bamboo leads to a difficulty in the extraction of protein using conventional methods, which seriously hinders research on the proteomics of moso bamboo. The purpose of this study is to establish efficient methods for extracting the total proteins from moso bamboo for following mass spectrometry-based quantitative proteome identification. Here, we have successfully established a set of efficient methods for extracting total proteins of moso bamboo followed by mass spectrometry-based label-free quantitative proteome identification, which further improved the protein annotation of moso bamboo genes. In this study, 10,376 predicted coding genes were confirmed by quantitative proteomics, accounting for 35.8% of all annotated protein-coding genes. Proteome analysis also revealed the protein-coding potential of 1015 predicted long noncoding RNA (lncRNA), accounting for 51.03% of annotated lncRNAs. Thus, mass spectrometry-based proteomics provides a reliable method for gene annotation. Especially, quantitative proteomics revealed the translation patterns of proteins in moso bamboo. In addition, the 3284 transcript isoforms from 2663 genes identified by Pacific BioSciences (PacBio) single-molecule real-time long-read isoform sequencing (Iso-Seq) was confirmed on the protein level by mass spectrometry. Furthermore, domain analysis of mass spectrometry-identified proteins encoded in the same genomic locus revealed variations in domain composition pointing towards a functional diversification of protein isoform. Finally, we found that part transcripts targeted by nonsense-mediated mRNA decay (NMD) could also be translated into proteins. In summary, proteomic analysis in this study improves the proteomics-assisted genome annotation of moso bamboo and is valuable to the large-scale research of functional genomics in moso bamboo. In summary, this study provided a theoretical basis and technical support for directional gene function analysis at the proteomics level in moso bamboo.