An Efficient Plant Regeneration and Transformation System of Ma Bamboo (Dendrocalamus latiflorus Munro) Started from Young Shoot as Explant

Auxin response factors fine-tune lignin biosynthesis in response to mechanical bending in bamboo

Lignin contributes to plant mechanical properties during bending loads. Meanwhile, phytohormone auxin controls various plant biological processes. However, the mechanism of auxin's role in bending-induced lignin biosynthesis was unclear, especially in bamboo, celebrated for its excellent deformation stability. Here, we reported that auxin response factors (ARF) 3 and ARF6 from Moso bamboo (Phyllostachys edulis (Carrière) J. Houz) directly regulate lignin biosynthesis pathway genes, and affect lignin biosynthesis in bamboo. Auxin and lignin exhibited asymmetric distribution patterns, and auxin promoted lignin biosynthesis in response to bending loads in bamboo. Employing transcriptomic and weighted gene co-expression network analysis approach, we discovered that expression patterns of ARF3 and ARF6 strongly correlated with lignin biosynthesis genes. ARF3 and ARF6 directly bind to the promoter regions of 4-coumarate: coenzyme A ligase (4CL3, 4CL7, and 4CL9) or caffeoyl-CoA O-methyltransferase (CCoAOMT2) genes, pivotal to lignin biosynthesis, and activate their expressions. Notably, the efficacy of this binding hinges on auxin levels. Alternation of the expressions of ARF3 and ARF6 substantially altered lignin accumulation in transgenic bamboo. Collectively, our study shed light on bamboo lignification genetics. Auxin signaling could directly modulate lignin biosynthesis genes to impact plant lignin content.

Comprehensive genome-wide analysis of the DREB gene family in Moso bamboo (Phyllostachys edulis): evidence for the role of PeDREB28 in plant abiotic stress response

Dehydration response element binding (DREB) proteins are vital for plant abiotic stress responses, but the understanding of DREBs in bamboo, an important sustainable non-timber forest product, is limited. Here we conducted a comprehensive genome-wide analysis of the DREB gene family in Moso bamboo, representing the most important running bamboo species in Asia. In total, 44 PeDREBs were identified, and information on their gene structures, protein motifs, phylogenetic relationships, and stress-related cis-regulatory elements (CREs) was provided. Based on the bioinformatical analysis, we further analyzed PeDREBs from the A5 group and found that four of five PeDREB transcripts were induced by salt, drought, and cold stresses, and their proteins could bind to stress-related CREs. Among these, PeDREB28 was selected as a promising candidate for further functional characterization. PeDREB28 is localized in nucleus, has transcriptional activation activity, and could bind to the DRE- and coupling element 1- (CE1) CREs. Overexpression of PeDREB28 in Arabidopsis and bamboo improved plant abiotic stress tolerance. Transcriptomic analysis showed that broad changes due to the overexpression of PeDREB28. Furthermore, 628 genes that may act as the direct PeDREB28 downstream genes were identified by combining DAP-seq and RNA-seq analysis. Moreover, we confirmed that PeDREB28 could bind to the promoter of pyrabactin-resistance-like gene (DlaPYL3), which is a homolog of abscisic acid receptor in Arabidopsis, and activates its expression. In summary, our study provides important insights into the DREB gene family in Moso bamboo, and contributes to their functional verification and genetic engineering applications in the future.

Identification and characterization of the cupin_1 domain-containing proteins in ma bamboo (Dendrocalamus latiflorus) and their potential role in rhizome sprouting

Cupin_1 domain-containing protein (CDP) family, which is a member of the cupin superfamily with the most diverse functions in plants, has been found to be involved in hormone pathways that are closely related to rhizome sprouting (RS), a vital form of asexual reproduction in plants. Ma bamboo is a typical clumping bamboo, which mainly reproduces by RS. In this study, we identified and characterized 53 Dendrocalamus latiflorus CDP genes and divided them into seven subfamilies. Comparing the genetic structures among subfamilies showed a relatively conserved gene structure within each subfamily, and the number of cupin_1 domains affected the conservation among D. latiflorus CDP genes. Gene collinearity results showed that segmental duplication and tandem duplication both contributed to the expansion of D. latiflorus CDP genes, and lineage-specific gene duplication was an important factor influencing the evolution of CDP genes. Expression patterns showed that CDP genes generally had higher expression levels in germinating underground buds, indicating that they might play important roles in promoting shoot sprouting. Transcription factor binding site prediction and co-expression network analysis indicated that D. latiflorus CDPs were regulated by a large number of transcription factors, and collectively participated in rhizome buds and shoot development. This study significantly provided new insights into the evolutionary patterns and molecular functions of CDP genes, and laid a foundation for further studying the regulatory mechanisms of plant rhizome sprouting.

Advancements and challenges in bamboo breeding for sustainable development

Bamboo is a highly renewable biomass resource with outstanding ecological, economic and social benefits. However, its lengthy vegetative growth stage and uncertain flowering period have hindered the application of traditional breeding methods. In recent years, significant progress has been made in bamboo breeding. While technical advances in bamboo breeding have been impressive, it is essential to also consider the broader implications we can learn from bamboo's extraordinary features for sustainable development. This review provides an overview of the current status of bamboo breeding technology, including a detailed history of bamboo breeding divided into four eras, a comprehensive map of bamboo germplasm gardens worldwide, with a focus on China, and a summary of available transgenic technologies for gene function verification and genetic improvement. As the demand for bamboo as a sustainable and renewable resource increases continuously, breeding objectives should be focused on enhancing yield, wood properties and adaptability to diverse environmental conditions. In particular, priority should be given to improving fiber length, internode length and wall thickness, as well as regulating lignin and cellulose content for papermaking, substitute for plastic and other applications. Furthermore, we highlight the challenges and opportunities for future research and development in bamboo breeding, including the application of omics technologies, artificial intelligence and the development of new breeding methods. Finally, by integrating the technical advances in bamboo breeding with a discussion of its broader implications for sustainable development, this review provides a comprehensive framework for the development of bamboo industry.

An effective method for establishing a regeneration and genetic transformation system for Actinidia arguta

The all-red A. arguta (Actinidia arguta) is an anthocyanin-rich and excellent hardy fruit. Many studies have focused on the green-fleshed A. arguta, and fewer studies have been conducted on the all-red A. arguta. Here we reported a regeneration and Agrobacterium-mediated transformation protocol by using leaves of all-red A. arguta as explants. Aseptic seedling leaves of A. arguta were used as callus-inducing materials. MS medium supplemented with 0.3 mg·L-1 2,4-D and 1.0 mg·L-1 BA was the optimal medium for callus induction of leaves, and medium supplemented with 3 mg·L-1 tZ and 0.5 mg·L-1 IAA was optimal for adventitious shoot regeneration. The best proliferation medium for adventitious buds was MS + 1.0 mg·L-1 BA + 0.3 mg·L-1 NAA. The best rooting medium was 1/2MS + 0.7 mg·L-1 IBA with a 100% rooting rate. For the red flesh hardy kiwi variety 'Purpurna Saduwa' (A. arguta var. purpurea), leaves are receptors for Agrobacterium (EHA105)-mediated transformation. The orthogonal experiment was used for the optimization of each genetic transformation parameter and the genetic transformation of the leaves was 21% under optimal conditions. Our study provides technical parameters for applying genetic resources and molecular breeding of kiwifruit with red flesh.

Establishment of Agrobacterium-mediated transformation system to Juglans sigillata Dode 'Qianhe-7'

An efficient genetic transformation system is of great significance for verifying gene function and improving plant breeding efficiency by gene engineering. In this study, a stable Agrobacterium mediated genetic transformation system of Juglans sigillata Dode 'Qianhe-7' was investigated using callus and negative pressure-assisted and ultrasonic-assisted transformation selection. The results showed that the axillary shoot leaves were suitable to induce callus and the callus proliferation rate could reach 516.27% when induction calli were cultured on DKW medium containing 0.5 mg L^-1 indole-3-butyric acid, 1.2 mg L^-1 2,4-dichlorophenoxyacetic acid and 0.5 mg L^-1 kinetin for 18 d. In addition, negative pressure infection was the optimal infection method with the lowest browning rate (0.00%), high GFP conversion rate (16.67%), and better growth status. To further prove the feasibility of this genetic transformation system, the flavonol synthetase (JsFLS₅) gene was successfully transformed into the into leaf-derived callus of 'Qianhe-7'. JsFLS₅ expression and the content of total flavonoids in transformed callus were improved significantly compared with the untransformed callus, which proved that we had an efficient and reliable genetic transformation system using leaf-derived callus of Juglans sigillata.

Shoot differentiation from Dendrocalamus brandisii callus and the related physiological roles of sugar and hormones during shoot differentiation

Only a few calli regeneration systems of bamboos were successfully established, which limited the research on physiological mechanism of callus differentiation. In this study, we successfully established the callus differentiation systems of Dendrocalamus brandisii via seeds. The results showed that the best medium for callus induction of D. brandisii seeds was basal MS media amended with 5.0 mg L-1 2,4-D and 0.5 mg L-1 KT, and the optimal medium for shoot differentiation was the basal MS media supplemented with 4.0 mg L-1 BA and 0.5 mg L-1 NAA. Callus tissues had apparent polarity in cell arrangement, and developed their own meristematic cell layers. α-amylase, STP and SUSY played a dominant role in carbohydrates degradation in callus during shoot differentiation. PPP and TCA pathways up-regulated in the shoot-differentiated calli. The dynamics of BA and KT contents in calli was consistent with their concentrations applied in medium. IAA synthesis and the related signal transduction were down-regulated, while the endogenous CTKs contents were up-regulated by the exogenous CTKs application in shoot-differentiated calli, and their related synthesis, transport and signal transduction pathways were also up-regulated. The downregulated signal transduction pathways of IAA and ABA revealed that they did not play the key role in shoot differentiation of bamboos. GAs also played a role in shoot differentiation based on the down-regulation of DELLA and the up-regulation of PIF4 genes. The overexpression of DbSNRK2 and DbFIF4 genes further confirmed the negative role of ABA and the positive role of GAs in shoot differentiation.

A new biotechnology for in-planta gene editing and its application in promoting flavonoid biosynthesis in bamboo leaves

BACKGROUND

Bamboo is a perennial and renewable biomass forest resource and its leaf flavonoid is an antioxidant for biological and pharmacological research. The established genetic transformation and gene editing systems in bamboo are significantly limited by the dependence on bamboo regeneration capability. The way to improve the flavonoid content in bamboo leaves through biotechnology is still not feasible.

RESULTS

Here, we developed an in-planta, Agrobacterium-mediated gene expression method for exogenous genes via wounding and vacuum in bamboo. We demonstrated that the RUBY served as a reporter efficiently expressed in bamboo leaves and shoots, albeit unable to integrate into the chromosome. We have also developed a gene editing system by creating an in situ mutant of the bamboo violaxanthin de-epoxidase (PeVDE) gene in bamboo leaves, with lower NPQ values under the fluorometer, which can serve as a native reporter for gene editing. Furthermore, the bamboo leaves with increased flavonoid content were achieved by knocking out the cinnamoyl-CoA reductase genes.

CONCLUSIONS

Our method can be applied for the functional characterization of novel genes in a short time and is helpful for bamboo leaf flavonoid biotechnology breeding in the future.

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.

Leaf transformation for efficient random integration and targeted genome modification in maize and sorghum

Transformation in grass species has traditionally relied on immature embryos and has therefore been limited to a few major Poaceae crops. Other transformation explants, including leaf tissue, have been explored but with low success rates, which is one of the major factors hindering the broad application of genome editing for crop improvement. Recently, leaf transformation using morphogenic genes Wuschel2 (Wus2) and Babyboom (Bbm) has been successfully used for Cas9-mediated mutagenesis, but complex genome editing applications, requiring large numbers of regenerated plants to be screened, remain elusive. Here we demonstrate that enhanced Wus2/Bbm expression substantially improves leaf transformation in maize and sorghum, allowing the recovery of plants with Cas9-mediated gene dropouts and targeted gene insertion. Moreover, using a maize-optimized Wus2/Bbm construct, embryogenic callus and regenerated plantlets were successfully produced in eight species spanning four grass subfamilies, suggesting that this may lead to a universal family-wide method for transformation and genome editing across the Poaceae.

Genome size and gas chromatography-mass spectrometry (GC-MS) analysis of field-grown and in vitro regenerated Pluchea lanceolata plants

Pluchea lanceolata is a threatened pharmacologically important plant from the family Asteraceae. It is a source of immunologically active compounds; large-scale propagation may offer compounds with medicinal benefits. Traditional propagation method is ineffective as the seeds are not viable; and root sprout propagation is a slow process and produces less numbers of plants. Plant tissue culture technique is an alternative, efficient method for increasing mass propagation and it also facilitate genetic improvement. The present study investigated a three-way regeneration system in P. lanceolata using indirect shoot regeneration (ISR), direct shoot regeneration (DSR), and somatic embryo mediated regeneration (SER). Aseptic leaf and nodal explants were inoculated on Murashige and Skoog (MS) medium amended with plant growth regulators (PGRs), 2,4-dichlorophenoxy acetic acid (2,4-D), 1-naphthalene acetic acid (NAA), and 6-benzyl amino purine (BAP) either singly or in combinations. Compact, yellowish green callus was obtained from leaf explants in 1.0 mg/l BAP (89.10%) added medium; ISR percentage was high, i.e., 69.33% in 2.0 mg/l BAP + 0.5 mg/l NAA enriched MS with 4.02 mean number of shoots per callus mass. Highest DSR frequency (67.15%) with an average of 5.62 shoot numbers per explant was noted in 0.5 mg/l BAP added MS medium. Somatic embryos were produced in 1.0 mg/l NAA fortified medium with 4.1 mean numbers of somatic embryos per culture. On BAP (1.0 mg/l) + 0.5 mg/l gibberellic acid (GA₃) amended medium, improved somatic embryo germination frequency (68.14%) was noted showing 12.18 mean numbers of shoots per culture. Histological and scanning electron microscopic (SEM) observation revealed different stages of embryos, confirming somatic embryogenesis in P. lanceolata. Best rooting frequency (83.95%) of in vitro raised shootlets was obtained in 1.0 mg/l IBA supplemented half MS medium with a maximum of 7.83 roots per shoot. The regenerated plantlets were transferred to the field with 87% survival rate. The 2C genome size of ISR, DSR, and SER plants was measured and noted to be 2.24, 2.25, and 2.22 pg respectively, which are similar to field-grown mother plant (2C = 2.26 pg). Oxidative and physiological events suggested upregulation of enzymatic activities in tissue culture regenerated plants compared to mother plants, so were photosynthetic pigments. Implementation of gas chromatography-mass spectrometry (GC-MS) technique on in vivo and in vitro raised plants revealed the presence of diverse phyto-chemicals. The yields of alpha amyrin and lupeol (medicinally important triterpenoids) were quantified using high-performance thin-layer chromatography (HPTLC) method and enhanced level of alpha amyrin (2.129 µg g^-1 dry wt) and lupeol (1.232 µg g^-1 dry wt) was noted in in vitro grown leaf tissues, suggesting in vitro conditions act as a potential trigger for augmenting secondary metabolite synthesis. The present protocol represents a reliable mass propagation technique in producing true-to-type plants of P. lanceolata, conserving 2C DNA and ploidy successfully without affecting genetic homogeneity.

The impact of genetic modified Ma bamboo on soil microbiome

Evaluating the potential alteration of microbial communities is a vital step for biosafety of genetic modified plants. Recently, we have produced genetic modified Ma bamboo with increased cold and drought tolerance by anthocyanin accumulation. In this work, we aim to study the potential effects on microbial communities in rhizosphere soils during the cultivation of genetic modified bamboo. Rhizosphere and surrounding soil were collected at 3-month post-transplant. The amplicon (16S rDNA and ITS1) were sequenced for analysis of bacterial and fungal communities. Multiple software and database (Picrust2, FAPROTAX and FUNGulid) were applied to predict and compare the microbial functions involving basic metabolisms, nitrogen usage and presence of plant pathogens. There were no substantial change of the structure and abundance of rhizosphere soil microbial communities between genetic modified and wild type bamboo. For the surrounding soil, the bacterial biota α-diversity increased (chao1: 1,001 ± 80-1,276 ± 84, observed species: 787 ± 52-1,194 ± 137, PD whole tree: 75 ± 4-117 ± 18) and fungal biota α-diversity decreased (chao1: 187 ± 18-145 ± 10) in samples of genetic modified bamboo compared to those of wild type bamboo. The microbiota predicted functions did not change or had no negative alteration between genetic modified and wild type bamboo, in both rhizosphere and surrounding soils. As a conclusion, the growth of genetic modified bamboo had no substantial change on rhizosphere soil microbial communities, while minor alteration on bamboo surrounding soil microbial communities with no harmful effects. Moreover, the genetic modified bamboo had no negative effect on the predicted functions of microbiota in soil.

A comprehensive analysis of the floral transition in ma bamboo (Dendrocalamus latiflorus) reveals the roles of DlFTs involved in flowering

Bamboo has a unique flowering characteristics of long and unpredictable vegetative period, which differs from annual herbs and perennial woody plants. In order to understand the molecular regulatory mechanism of bamboo flowering, a comprehensive study was conducted in ma bamboo (Dendrocalamus latiflorus Munro), including morphological, physiological and transcriptiome analyses. Differentially expressed genes related to the flowering pathway were identified by comparative transcriptome analysis. DlFT1, a homologous gene of FT/Hd3a, was significantly upregulated in flowering bamboo. Direct differentiation of spikelets from calli occurred and the downstream gene AP1 was upregulated in the transgenic bamboo overexpressing DlFT1. Transgenic rice overexpressing DlFT1 showed a strong early flowering phenotype. DlFT1 and DlTFL1 could interact with DlFD, and DlTFL1 delayed flowering. It is presumed that DlTFL1 plays an antagonistic role with DlFT1 in ma bamboo. In addition, the expression of DlFT1 was regulated by DlCO1, indicating that a CO-FT regulatory module might exist in ma bamboo. These results suggest that DlFT1 is a florigen candidate gene with conservative function in promoting flowering. Interestingly, the results have shown for the first time that DlFT2 can specifically interact with E3 ubiquitin ligase WAV3, while DlFT3 transcripts are mainly nonsense splicing. These findings provide better understanding of the roles of the florigen gene in bamboo and lay a theoretical basis for regulating bamboo flowering in the future.

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.

An Efficient Genetic Transformation and CRISPR/Cas9-Based Genome Editing System for Moso Bamboo (Phyllostachys edulis)

Moso bamboo (Phyllostachys edulis) is the most important monopodial bamboo species worldwide. Without a genetic transformation system, it is difficult to verify the functions of genes controlling important traits and conduct molecular breeding in moso bamboo. Here, we established a plant regeneration system from immature embryos. Calli were induced on MS medium added 4-6 mg⋅L-1 2,4-dichlorophenoxyacetic acid (2,4-D) with high efficiency (>60%). A plant growth regulator combination of 0.5 mg⋅L-1 1-naphthylacetic acid (NAA), 2.0 mg⋅L-1 6-benzylaminopurine (BAP), and 3.0 mg⋅L-1 zeatin (ZT) was suitable for shoot differentiation, and the shoot induction frequency was increased to 43% after 0.5 mg⋅L-1 abscisic acid (ABA) pretreatment. An effective antibiotic screening concentration was determined by hygromycin sensitivity test. We further optimized the Agrobacterium concentration and added vacuum infiltration for infection, which improves the transient expression efficiency. A genetic transformation system was established for the first time in moso bamboo, with the transformation efficiency of approximately 5%. To optimize genome editing, two endogenous U3 small nuclear RNA (snRNA) promoters were isolated and used to drive small guide RNA (sgRNA) expression. The results showed that the PeU3.1 promoter exhibited higher efficiency, and it was used for subsequent genome editing. Finally, homozygous pds1pds2 mutants were obtained by an efficient CRISPR/Cas9 genome-editing system. These technical systems will be conducive to gene functional validation and accelerate the molecular breeding process of moso bamboo.

Ectopic Overexpression of Maize Heat Stress Transcription Factor ZmHsf05 Confers Drought Tolerance in Transgenic Rice

Drought is a key factor affecting plant growth and development. Heat shock transcription factors (Hsfs) have been reported to respond to diverse abiotic stresses, including drought stress. In the present study, functional characterization of maize heat shock transcription factor 05 (ZmHsf05) gene was conducted. Homologous analysis showed that ZmHsf05 belongs to Class A2 Hsfs. The mRNA expression level of ZmHsf05 can be affected by drought, high temperature, salt, and abscisic acid (ABA) treatment. Ectopic overexpression of ZmHsf05 in rice (Oryza sativa) could significantly enhance the drought tolerance. Faced with drought stress, transgenic rice exhibited better phenotypic performance, higher survival rate, higher proline content, and lower leaf water loss rate, compared with wild-type plant Zhonghua11. Additionally, we assessed the agronomic traits of seven transgenic rice lines overexpressing ZmHsf05 and found that ZmHsf05 altered agronomical traits in the field trials. Moreover, rice overexpressing ZmHsf05 was more sensitive to ABA and had either a lower germination rate or shorter shoot length under ABA treatment. The transcription level of key genes in the ABA synthesis and drought-related pathway were significantly improved in transgenic rice after drought stress. Collectively, our results showed that ZmHsf05 could improve drought tolerance in rice, likely in an ABA-dependent manner.

A Concise Review of Dendrocalamus asper and Related Bamboos: Germplasm Conservation, Propagation and Molecular Biology

Bamboos represent an emerging forest resource of economic significance and provide an avenue for sustainable development of forest resources. The development of the commercial bamboo industry is founded upon efficient molecular and technical approaches for the selection and rapid multiplication of elite germplasm for its subsequent propagation via commercial agro-forestry business enterprises. This review will delve into the micropropagation of Dendrocalamus asper, one of the most widely cultivated commercial varieties of bamboo, and will encompass the selection of germplasm, establishment of explants in vitro and micropropagation techniques. The currently available information pertaining to molecular biology, DNA barcoding and breeding, has been included, and potential areas for future research in the area of genetic engineering and gene regulation have been highlighted. This information will be of relevance to both commercial breeders and molecular biologists who have an interest in establishing bamboo as a crop of the future.

The transcriptional dynamics during de novo shoot organogenesis of Ma bamboo (Dendrocalamus latiflorus Munro): implication of the contributions of the abiotic stress response in this process

De novo shoot organogenesis is an important biotechnological tool for fundamental studies in plant. However, it is difficult in most bamboo species, and the genetic control of this highly dynamic and complicated regeneration process remains unclear. In this study, based on an in-depth analysis at the cellular level, the shoot organogenesis from calli of Ma bamboo (Dendrocalamus latiflorus Munro) was divided into five stages. Subsequently, single-molecule long-read isoform sequencing of tissue samples pooled from all five stages was performed to generate a full-length transcript landscape. A total of 83 971 transcripts, including 73 209 high-quality full-length transcripts, were captured, which served as an annotation reference for the subsequent RNA sequencing analysis. Time-course transcriptome analysis of samples at the abovementioned five stages was conducted to investigate the global gene expression atlas showing genome-wide expression of transcripts during the course of bamboo shoot organogenesis. K-means clustering analysis and stage-specific transcript identification revealed important dynamically expressed transcription regulators that function in bamboo shoot organogenesis. The majority of abiotic stress-responsive genes altered their expression levels during this process, and further experiments demonstrated that exogenous application of moderate but not severe abiotic stress increased the shoot regeneration efficiency. In summary, our study provides an overview of the genetic flow dynamics during bamboo shoot organogenesis. Full-length cDNA sequences generated in this study can serve as a valuable resource for fundamental and applied research in bamboo in the future.

Production of purple Ma bamboo (Dendrocalamus latiflorus Munro) with enhanced drought and cold stress tolerance by engineering anthocyanin biosynthesis

Overexpression of the leaf color (Lc) gene in Ma bamboo substantially increased the accumulation level of anthocyanin, and improved plant tolerance to cold and drought stresses, probably due to the increased antioxidant capacity. Most bamboos, including Ma bamboo (Dendrocalamus latiflorus Munro), are naturally evergreen and sensitive to cold and drought stresses, while it's nearly impossible to make improvements through conventual breeding due to their long and irregular flowering habit. Moreover, few studies have reported bamboo germplasm innovation through genetic engineering as bamboo genetic transformation remains difficult. In this study, we have upregulated anthocyanin biosynthesis in Ma bamboo, to generate non-green Ma bamboo with increased abiotic stress tolerance. By overexpressing the maize Lc gene, a bHLH transcription activator involved in the anthocyanin biosynthesis in Ma bamboo, we generated purple bamboos with increased anthocyanin levels including cyanidin-3-O-rutinoside, peonidin 3-O-rutinoside, and an unknown cyanidin pentaglycoside derivative. The expression levels of 9 anthocyanin biosynthesis genes were up-regulated. Overexpression of the Lc gene improved the plant tolerance to cold and drought stress, probably due to increased antioxidant capacity. The levels of the cold- and drought-related phytohormone jasmonic acid in the transgenic plants were also enhanced, which may also contribute to the plant stress-tolerant phenotypes. High anthocyanin accumulation level did not affect plant growth. Transcriptomic analysis showed higher expressions of genes involved in the flavonoid pathway in Lc transgenic bamboos compared with those in wild-type ones. The anthocyanin-rich bamboos generated here provide an example of ornamental and multiple agronomic trait improvements by genetic engineering in this important grass species.

An Efficient Agrobacterium Mediated Transformation of Pineapple with GFP-Tagged Protein Allows Easy, Non-Destructive Screening of Transgenic Pineapple Plants

Quite a few studies have been conducted to improve the Agrobacterium-mediated transformation of pineapple, which is the second most important commercial tropical fruit crop worldwide. However, pineapple transformation remains challenging, due to technical difficulties, the lengthy regeneration process, and a high labor requirement. There have not been any studies specifically addressing the introduction of GFP-tagged genes into pineapples through Agrobacterium-mediated transformation, which would enable easy, non-destructive expression detection. It would also allow expression localization at the organelle level, which is not possible with GUS a reporter gene that encodes β-glucuronidase or a herbicide resistance reporter gene. Here, we report a method for the introduction of GFP-tagged genes into pineapples through Agrobacterium-mediated transformation. We used embryonic calli for transformation, and plants were regenerated through somatic embryogenesis. In this study, we optimized the incubation time for Agrobacterium infection, the co-cultivation time, the hygromycin concentration for selection, and the callus growth conditions after selection. Our strategy reduced the time required to obtain transgenic plants from 7.6 months to 6.1 months. The expression of GFP-tagged AcWRKY28 was observed in the nuclei of transgenic pineapple root cells. This method allows easy, non-destructive expression detection of transgenic constructs at the organelle level. These findings on pineapple transformation will help accelerate pineapple molecular breeding efforts to introduce new desirable traits.

Morphological dissection and cellular and transcriptome characterizations of bamboo pith cavity formation reveal a pivotal role of genes related to programmed cell death

Pith cavity formation is critical for bamboo to overcome the bending force during its fast growth; however, the underlying molecular mechanisms remain largely unknown. Multiple approaches, including anatomical dissection, mathematical modelling and transcriptome profiling, were employed in this study to investigate the biology of pith cavity formation in bamboo Pseudosasa japonica. We found that the corruption of pith tissue occurred sequentially and asymmetrically from the top-centre of the internode down to the bottom, which might be caused by the combined effects of asymmetrical radial and axial tensile forces during shoot-wall cell elongation and spiral growth of bamboo internodes. Programmed cell death (PCD) in pitch manifested by TUNEL positive nuclei, DNA cleavage and degraded organelles, and potentially regulated by ethylene and calcium signalling pathway, ROS burst, cell wall modification, proteolysis and nutrient recycle genes, might be responsible for pith tissue corruption of Ps. japonica. Although similar physiological changes and transcriptome profiles were found in different bamboo species, different formation rates of pith cavity were observed, which might be caused by different pith cells across the internode that were negatively correlated with the culm diameter. These findings provided a systematical view on the formation of bamboo pith cavity and revealed that PCD plays an important role in the bamboo pith cavity formation.

Overexpression of a MYB Family Gene, OsMYB6, Increases Drought and Salinity Stress Tolerance in Transgenic Rice

MYB transcription factors have been demonstrated to play key regulatory roles in plant growth, development and abiotic stress response. However, knowledge concerning the involvement of rice MYB genes in salinity and drought stress resistance are largely unknown. In the present study, we cloned and characterized the OsMYB6 gene, which was induced by drought and salinity stress. Subcellular localization of OsMYB6-YFP fusion protein in protoplast cells indicated that OsMYB6 was localized in the nucleus. Overexpression of OsMYB6 in rice did not suggest a negative effect on the growth and development of transgenic plants, but OsMYB6-overexpressing plants showed increased tolerance to drought and salt stress compared with wild-type plants, as are evaluated by higher proline content, higher CAT and SOD activities, lower REL and MDA content in transgenic plants under drought and salt stress conditions. In addition, the expression of abiotic stress-responsive genes were significantly higher in OsMYB6 transgenic plants than that in wild-type plants under drought and salt stress conditions. These results indicate that OsMYB6 gene functions as a stress-responsive transcription factor which plays a positive regulatory role in response to drought and salt stress resistance, and may be used as a candidate gene for molecular breeding of salt-tolerant and drought-tolerant crop varieties.

Overexpression of PvCO1, a bamboo CONSTANS-LIKE gene, delays flowering by reducing expression of the FT gene in transgenic Arabidopsis

BACKGROUND

In Arabidopsis, a long day flowering plant, CONSTANS (CO) acts as a transcriptional activator of flowering under long day (LD) condition. In rice, a short day flowering plant, Hd1, the ortholog of CO, plays dual functions in respond to day-length, activates flowering in short days and represses flowering in long days. In addition, alleles of Hd1 account for ~ 44% of the variation in flowering time observed in cultivated rice and sorghum. How does it work in bamboo? The function of CO in bamboo is similar to that in Arabidopsis?

RESULTS

Two CO homologous genes, PvCO1 and PvCO2, in Phyllostachys violascens were identified. Alignment analysis showed that the two PvCOLs had the highest sequence similarity to rice Hd1. Both PvCO1 and PvCO2 expressed in specific tissues, mainly in leaf. The PvCO1 gene had low expression before flowering, high expression during the flowering stage, and then declined to low expression again after flowering. In contrast, expression of PvCO2 was low during the flowering stage, but rapidly increased to a high level after flowering. The mRNA levels of both PvCOs exhibited a diurnal rhythm. Both PvCO1 and PvCO2 proteins were localized in nucleus of cells. PvCO1 could interact with PvGF14c protein which belonged to 14-3-3 gene family through B-box domain. Overexpression of PvCO1 in Arabidopsis significantly caused late flowering by reducing the expression of AtFT, whereas, transgenic plants overexpressing PvCO2 showed a similar flowering time with WT under LD conditions. Taken together, these results suggested that PvCO1 was involved in the flowering regulation, and PvCO2 may either not have a role in regulating flowering or act redundantly with other flowering regulators in Arabidopsis. Our data also indicated regulatory divergence between PvCOLs in Ph. violascens and CO in Arabidopsis as well as Hd1 in Oryza sativa. Our results will provide useful information for elucidating the regulatory mechanism of COLs involved in the flowering.

CONCLUSIONS

Unlike to the CO gene in Arabidopsis, PvCO1 was a negative regulator of flowering in transgenic Arabidopsis under LD condition. It was likely that long period of vegetative growth of this bamboo species was related with the regulation of PvCO1.

Use of a temporary immersion bioreactor system for the sustainable production of thapsigargin in shoot cultures of Thapsia garganica

BACKGROUND

Thapsigargin and nortrilobolide are sesquiterpene lactones found in the Mediterranean plant Thapsia garganica L. Thapsigargin is a potent inhibitor of the sarco/endoplasmic reticulum calcium ATPase pump, inducing apoptosis in mammalian cells. This mechanism has been used to develop a thapsigargin-based cancer drug first by GenSpera and later Inspyr Therapeutics (Westlake Village, California). However, a stable production of thapsigargin is not established.

RESULTS

In vitro regeneration from leaf explants, shoot multiplication and rooting of T. garganica was obtained along with the production of thapsigargins in temporary immersion bioreactors (TIBs). Thapsigargin production was enhanced using reduced nutrient supply in combination with methyl jasmonate elicitation treatments. Shoots grown in vitro were able to produce 0.34% and 2.1% dry weight of thapsigargin and nortrilobolide, respectively, while leaves and stems of wild T. garganica plants contain only between 0.1 and 0.5% of thapsigargin and below detectable levels of nortrilobolide. In addition, a real-time reverse transcription PCR (qRT-PCR) study was performed to study the regulatory role of the biosynthetic genes HMG-CoA reductase (HMGR), farnesyl diphosphate synthase (FPPS), epikunzeaol synthase (TgTPS2) and the cytochrome P450 (TgCYP76AE2) of stem, leaf and callus tissues. Nadi staining showed that the thapsigargins are located in secretory ducts within these tissues.

CONCLUSIONS

Shoot regeneration, rooting and biomass growth from leaf explants of T. garganica were achieved, together with a high yield in vitro production of thapsigargin in TIBs.