PagPXYs improve drought tolerance by regulating reactive oxygen species homeostasis in the cambium of Populus alba × P. glandulosa

PXY (Phloem intercalated with xylem) is a receptor kinase required for directional cell division during the development of plant vascular tissue. Drought stress usually affects plant stem cell division and differentiation thereby limiting plant growth. However, the role of PXY in cambial activities of woody plants under drought stress is unclear. In this study, we analyzed the biological functions of two PXY genes (PagPXYa and PagPXYb) in poplar growth and development and in response to drought stress in a hybrid poplar (Populus alba × P. glandulosa, '84K'). Expression analysis indicated that PagPXYs, similar to their orthologs PtrPXYs in Populus trichocarpa, are mainly expressed in the stem vascular system, and related to drought. Interestingly, overexpression of PagPXYa and PagPXYb in poplar did not have a significant impact on the growth status of transgenic plants under normal condition. However, when treated with 8 % PEG6000 or 100 mM H2O2, PagPXYa and PagPXYb overexpressing lines consistently exhibited more cambium cell layers, fewer xylem cell layers, and enhanced drought tolerance compared to the non-transgenic control '84K'. In addition, PagPXYs can alleviate the damage caused by H2O2 to the cambium under drought stress, thereby maintaining the cambial division activity of poplar under drought stress, indicating that PagPXYs play an important role in plant resistance to drought stress. This study provides a new insight for further research on the balance of growth and drought tolerance in forest trees.

PagWOX11/12a from hybrid poplar enhances drought tolerance by modulating reactive oxygen species

WOX11/12 is a homeobox gene of WOX11 and WOX12 in Arabidopsis that plays important roles in crown root development and growth. It has been reported that WOX11/12 participates in adventitious root (AR) formation and different abiotic stress responses, but the downstream regulatory network of WOX11/12 in poplar remains to be further investigated. In this study, we found that PagWOX11/12a is strongly induced by PEG-simulated drought stress. PagWOX11/12a-overexpressing poplar plantlets showed lower oxidative damage levels, greater antioxidant enzyme activities and reactive oxygen species (ROS) scavenging capacity than non-transgenic poplar plants, whereas PagWOX11/12a dominant repression weakened root biomass accumulation and drought tolerance in poplar. RNA-seq analysis revealed that several differentially expressed genes (DEGs) regulated by PagWOX11/12a are involved in redox metabolism and drought stress response. We used RT-qPCR and yeast one-hybrid (Y1H) assays to validate the downstream target genes of PagWOX11/12a. These results provide new insights into the biological function and molecular regulatory mechanism of WOX11/12 in the abiotic resistance processes of poplar.

Profiling of the gene expression and alternative splicing landscapes of Eucalyptus grandis

Eucalyptus is a widely planted hardwood tree species due to its fast growth, superior wood properties and adaptability. However, the post-transcriptional regulatory mechanisms controlling tissue development and stress responses in Eucalyptus remain poorly understood. In this study, we performed a comprehensive analysis of the gene expression profile and the alternative splicing (AS) landscape of E. grandis using strand-specific RNA-Seq, which encompassed 201 libraries including different organs, developmental stages, and environmental stresses. We identified 10 416 genes (33.49%) that underwent AS, and numerous differentially expressed and/or differential AS genes involved in critical biological processes, such as primary-to-secondary growth transition of stems, adventitious root formation, aging and responses to phosphorus- or boron-deficiency. Co-expression analysis of AS events and gene expression patterns highlighted the potential upstream regulatory role of AS events in multiple processes. Additionally, we highlighted the lignin biosynthetic pathway to showcase the potential regulatory functions of AS events in the KNAT3 and IRL3 genes within this pathway. Our high-quality expression atlas and AS landscape serve as valuable resources for unravelling the genetic control of woody plant development, long-term adaptation, and understanding transcriptional diversity in Eucalyptus. Researchers can conveniently access these resources through the interactive ePlant browser (https://bar.utoronto.ca/eplant_eucalyptus).

Growth-regulating factor 15-mediated vascular cambium differentiation positively regulates wood formation in hybrid poplar (Populus alba × P. glandulosa)

Introduction

Hybrid poplars are industrial trees in China. An understanding of the molecular mechanism underlying wood formation in hybrid poplars is necessary for molecular breeding. Although the division and differentiation of vascular cambial cells is important for secondary growth and wood formation, the regulation of this process is largely unclear.

Methods

In this study, mPagGRF15 OE and PagGRF15-SRDX transgenic poplars were generated to investigate the function of PagGRF15. RNA-seq and qRT-PCR were conducted to analyze genome-wide gene expression, while ChIP‒seq and ChIP-PCR were used to identified the downstream genes regulated by PagGRF15.

Results and discussion

We report that PagGRF15 from hybrid poplar (Populus alba × P. glandulosa), a growth-regulating factor, plays a critical role in the regulation of vascular cambium activity. PagGRF15 was expressed predominantly in the cambial zone of vascular tissue. Overexpression of mPagGRF15 (the mutated version of GRF15 in the miR396 target sequence) in Populus led to decreased plant height and internode number. Further stem cross sections showed that the mPagGRF15 OE plants exhibited significant changes in vascular pattern with an increase in xylem and a reduction in phloem. In addition, cambium cell files were decreased in the mPagGRF15 OE plants. However, dominant suppression of the downstream genes of PagGRF15 using PagGRF15-SRDX showed an opposite phenotype. Based on the RNA-seq and ChIP-seq results, combining qRT-PCR and ChIP-PCR analysis, candidate genes, such as WOX4b, PXY and GID1.3, were obtained and found to be mainly involved in cambial activity and xylem differentiation. Accordingly, we speculated that PagGRF15 functions as a positive regulator mediating xylem differentiation by repressing the expression of the WOX4a and PXY genes to set the pace of cambial activity. In contrast, PagGRF15 mediated the GA signaling pathway by upregulating GID1.3 expression to stimulate xylem differentiation. This study provides valuable information for further studies on vascular cambium differentiation mechanisms and genetic improvement of the specific gravity of wood in hybrid poplars.

Woody plant cell walls: Fundamentals and utilization

Cell walls in plants, particularly forest trees, are the major carbon sink of the terrestrial ecosystem. Chemical and biosynthetic features of plant cell walls were revealed early on, focusing mostly on herbaceous model species. Recent developments in genomics, transcriptomics, epigenomics, transgenesis, and associated analytical techniques are enabling novel insights into formation of woody cell walls. Here, we review multilevel regulation of cell wall biosynthesis in forest tree species. We highlight current approaches to engineering cell walls as potential feedstock for materials and energy and survey reported field tests of such engineered transgenic trees. We outline opportunities and challenges in future research to better understand cell type biogenesis for more efficient wood cell wall modification and utilization for biomaterials or for enhanced carbon capture and storage.

Overexpression of REDUCED WALL ACETYLATION C increases xylan acetylation and biomass recalcitrance in Populus

Plant lignocellulosic biomass, i.e. secondary cell walls of plants, is a vital alternative source for bioenergy. However, the acetylation of xylan in secondary cell walls impedes the conversion of biomass to biofuels. Previous studies have shown that REDUCED WALL ACETYLATION (RWA) proteins are directly involved in the acetylation of xylan but the regulatory mechanism of RWAs is not fully understood. In this study, we demonstrate that overexpression of a Populus trichocarpa PtRWA-C gene increases the level of xylan acetylation and increases the lignin content and S/G ratio, ultimately yielding poplar woody biomass with reduced saccharification efficiency. Furthermore, through gene coexpression network and expression quantitative trait loci (eQTL) analysis, we found that PtRWA-C was regulated not only by the secondary cell wall hierarchical regulatory network but also by an AP2 family transcription factor HARDY (HRD). Specifically, HRD activates PtRWA-C expression by directly binding to the PtRWA-C promoter, which is also the cis-eQTL for PtRWA-C. Taken together, our findings provide insights into the functional roles of PtRWA-C in xylan acetylation and consequently saccharification and shed light on synthetic biology approaches to manipulate this gene and alter cell wall properties. These findings have substantial implications for genetic engineering of woody species, which could be used as a sustainable source of biofuels, valuable biochemicals, and biomaterials.

Insights into cryptochrome modulation of ABA signaling to mediate dormancy regulation in Marchantia polymorpha

The acquisition of dormancy capabilities has enabled plants to survive in adverse terrestrial environmental conditions. Dormancy accumulation and release is coupled with light signaling, which is well studied in Arabidopsis, but it is unclear in the distant nonvascular relative. We study the characteristics and function on dormancy regulation of a blue light receptor cryptochrome in Marchantia polymorpha (MpCRY). Here, we identified MpCRY via bioinformatics and mutant complement analysis. The biochemical characteristics were assessed by multiple protein-binding assays. The function of MpCRY in gemma dormancy was clarified by overexpression and mutation of MpCRY, and its mechanism was analyzed via RNA sequencing and quantitative PCR analyses associated with hormone treatment. We found that the unique MpCRY protein in M. polymorpha undergoes both blue light-promoted interaction with itself (self-interaction) and blue light-dependent phosphorylation. MpCRY has the specific characteristics of blue light-induced nuclear localization and degradation. We further demonstrated that MpCRY transcriptionally represses abscisic acid (ABA) signaling-related gene expression to suppress gemma dormancy, which is dependent on blue light signaling. Our findings indicate that MpCRY possesses specific biochemical and molecular characteristics, and modulates ABA signaling under blue light conditions to regulate gemma dormancy in M. polymorpha.

PagERF81 regulates lignin biosynthesis and xylem cell differentiation in poplar

Lignin is a major component of plant cell walls and is essential for plant growth and development. Lignin biosynthesis is controlled by a hierarchical regulatory network involving multiple transcription factors. In this study, we showed that the gene encoding an APETALA 2/ethylene-responsive element binding factor (AP2/ERF) transcription factor, PagERF81, from poplar 84 K (Populus alba × P. glandulosa) is highly expressed in expanding secondary xylem cells. Two independent homozygous Pagerf81 mutant lines created by gene editing, produced significantly more but smaller vessel cells and longer fiber cells with more lignin in cell walls, while PagERF81 overexpression lines had less lignin, compared to non-transgenic controls. Transcriptome and reverse transcription quantitative PCR data revealed that multiple lignin biosynthesis genes including Cinnamoyl CoA reductase 1 (PagCCR1), Cinnamyl alcohol dehydrogenase 6 (PagCAD6), and 4-Coumarate-CoA ligase-like 9 (Pag4CLL9) were up-regulated in Pagerf81 mutants, but down-regulated in PagERF81 overexpression lines. In addition, a transient transactivation assay revealed that PagERF81 repressed the transcription of these three genes. Furthermore, yeast one hybrid and electrophoretic mobility shift assays showed that PagERF81 directly bound to a GCC sequence in the PagCCR1 promoter. No known vessel or fiber cell differentiation related genes were differentially expressed, so the smaller vessel cells and longer fiber cells observed in the Pagerf81 lines might be caused by abnormal lignin deposition in the secondary cell walls. This study provides insight into the regulation of lignin biosynthesis, and a molecular tool to engineer wood with high lignin content, which would contribute to the lignin-related chemical industry and carbon sequestration.

[Investigate of the etiology and prevention status of liver cirrhosis]

Objective: To investigate the etiology, prevention and treatment status, and their corresponding regional differences of the patients with liver cirrhosis in China, in order to provide scientific basis for the development of diagnosis and control strategies in China. Methods: Clinical data of patients diagnosed with liver cirrhosis for the first time through January 1, 2018 to December 31, 2020 from 50 hospitals in seven different regions of China were collected and analyzed retrospectively, and the difference of etiology, treatment, and their differences in various regions were analyzed. Results: A total of 11 861 cases with liver cirrhosis were included in the study. Thereinto, 5 093 cases (42.94%) were diagnosed as compensated cirrhosis, and 6 768 cases (57.06%) had decompensated cirrhosis. Notably, 8 439 cases (71.15%) were determined as chronic hepatitis B-caused cirrhosis, 1 337 cases (11.27%) were alcoholic liver disease, 963 cases (8.12%) were chronic hepatitis C, 698 cases (5.88%) were autoimmune liver disease, 367 cases (3.09%) were schistosomiasis, 177 cases (1.49%) were nonalcoholic fatty liver, and 743 cases (6.26%) of other types of liver disease. There were significant differences in the incidence of chronic hepatitis B, chronic hepatitis C, alcoholic liver disease, fatty liver, schistosomiasis liver disease, and autoimmune liver disease among the seven regions (P<0.001). Only 1 139 cases (9.60%) underwent endoscopic therapy, thereinto, 718 cases (6.05%) underwent surgical therapy, and 456 cases (3.84%) underwent interventional therapy treatment. In patients with compensated liver cirrhosis, 60 cases (0.51%) underwent non-selective β receptor blockers(NSBB), including 59 cases (0.50%) underwent propranolol and 1 case (0.01%) underwent carvedilol treatment. In patients with decompensated liver cirrhosis, 310 cases (2.61%) underwent NSBB treatment, including 303 cases (2.55%) underwent propranolol treatment and 7 cases (0.06%) underwent carvedilol treatment. Interestingly, there were significant differences in receiving endoscopic therapy, interventional therapy, NSBB therapy, splenectomy and other surgical treatments among the seven regions (P<0.001). Conclusion: Currently, chronic hepatitis B is the main cause (71.15%) of liver cirrhosis in several regions of China, and alcoholic liver disease has become the second cause (11.27%) of liver cirrhosis in China. The three-level prevention and control of cirrhosis in China should be further strengthened.

PagWOX11/12a positively regulates the PagSAUR36 gene that enhances adventitious root development in poplar

Adventitious root (AR) development is an extremely complex biological process that is affected by many intrinsic factors and extrinsic stimuli. Some WUSCHEL-related homeobox (WOX) transcription factors have been reported to play important roles in AR development, but their functional relationships with auxin signaling are poorly understood, especially the developmental plasticity of roots in response to adversity stress. Here, we identified that the WOX11/12a-SMALL AUXIN UP RNA36 (SAUR36) module mediates AR development through the auxin pathway in poplar, as well as under salt stress. PagWOX11/12a displayed inducible expression during AR development, and overexpression of PagWOX11/12a significantly promoted AR development and increased salt tolerance in poplar, whereas dominant repression of PagWOX11/12a produced the opposite phenotype. PagWOX11/12a proteins directly bind to the SAUR36 promoter to regulate SAUR36 transcription, and this binding was enhanced during salt stress. Genetic modification of PagWOX11/12a-PagSAUR36 expression revealed that the PagWOX11/12a-PagSAUR36 module is crucial for controlling AR development via the auxin pathway. Overall, our results indicate that a novel WOX11-SAUR-auxin signaling regulatory module is required for AR development in poplar. These findings provide key insights and a better understanding of the involvement of WOX11 in root developmental plasticity in saline environments.

PdeHCA2 affects biomass in Populus by regulating plant architecture, the transition from primary to secondary growth, and photosynthesis

PdeHCA2 regulates the transition from primary to secondary growth, plant architecture, and affects photosynthesis by targeting PdeBRC1 and controlling the anatomy of the mesophyll, and intercellular space, respectively. Branching, secondary growth, and photosynthesis are vital developmental processes of woody plants that determine plant architecture and timber yield. However, the mechanisms underlying these processes are unknown. Here, we report that the Populus transcription factor High Cambium Activity 2 (PdeHCA2) plays a role in the transition from primary to secondary growth, vascular development, and branching. In Populus, PdeHCA2 is expressed in undifferentiated provascular cells during primary growth, in phloem cells during secondary growth, and in leaf veins, which is different from the expression pattern of its homolog in Arabidopsis. Overexpression of PdeHCA2 has pleiotropic effects on shoot and leaf development; overexpression lines showed delayed growth of shoots and leaves, reduced photosynthesis, and abnormal shoot branching. In addition, auxin-, cytokinin-, and photosynthesis-related genes were differentially regulated in these lines. Electrophoretic mobility shift assays and transcriptome analysis indicated that PdeHCA2 directly up-regulates the expression of BRANCHED1 and the MADS-box gene PdeAGL9, which regulate plant architecture, by binding to cis-elements in the promoters of these genes. Taken together, our findings suggest that HCA2 regulates several processes in woody plants including vascular development, photosynthesis, and branching by affecting the proliferation and differentiation of parenchyma cells.

The role of senescence-associated gene101 (PagSAG101a) in the regulation of secondary xylem formation in poplar

Wood is produced by the accumulation of secondary xylem via proliferation and differentiation of the cambium cells in woody plants. Identifying the regulators involved in this process remains a challenging task. In this study, we isolated PagSAG101a, the homolog of Arabidopsis thaliana SAG101, from a hybrid poplar (Populus alba × Populus glandulosa) clone 84K and investigated its role in secondary xylem development. PagSAG101a was expressed predominantly in lignified stems and localized in the nucleus. Compared with non-transgenic 84K plants, transgenic plants overexpressing PagSAG101a displayed increased plant height, internode number, stem diameter, xylem width, and secondary cell wall thickness, while opposite phenotypes were observed for PagSAG101a knock-out plants. Transcriptome analyses revealed that differentially expressed genes were enriched for those controlling cambium cell division activity and subsequent secondary cell wall deposition during xylem formation. In addition, the tandem CCCH zinc finger protein PagC3H17, which positively regulates secondary xylem width and secondary wall thickening in poplar, could bind to the promoter of PagSAG101a and mediate the regulation of xylem differentiation. Our results support that PagSAG101a, downstream of PagC3H17, functions in wood development.

PagGRF12a interacts with PagGIF1b to regulate secondary xylem development through modulating PagXND1a expression in Populus alba × P. glandulosa

Growth-regulating factors (GRFs) are important regulators of plant development and growth, but their possible roles in xylem development in woody plants remain unclear. Here, we report that Populus alba × Papulus glandulosa PagGRF12a negatively regulates xylem development in poplar. PagGRF12a is expressed in vascular tissues. Compared to non-transgenic control plants, transgenic poplar plants overexpressing PagGRF12a exhibited reduced xylem width and plants with repressed expression of PagGRF12a exhibited increased xylem width. Xylem NAC domain 1 (XND1) encodes a NAC domain transcription factor that regulates xylem development and transcriptional analyses revealed that PagXND1a is highly upregulated in PagGRF12a-overexpressing plants and downregulated in PagGRF12a-suppressed plants, indicating that PagGRF12a may regulate xylem development through PagXND1a. Transient transcriptional assays and chromatin immunoprecipitation-polymerase chain reaction assays confirmed that PagGRF12a directly upregulates PagXND1a. In addition, PagGRF12a interacts with the GRF-Interacting Factor (GIF) PagGIF1b, and this interaction enhances the effects of PagGRF12a on PagXND1a. Our results indicate that PagGRF12a inhibits xylem development by upregulating the expression of PagXND1a.

Transcriptional Regulation and Signaling of Developmental Programmed Cell Death in Plants

Developmental programmed cell death (dPCD) has multiple functions in plant growth and development, and is of great value for industrial production. Among them, wood formed by xylem dPCD is one of the most widely used natural materials. Therefore, it is crucial to explore the molecular mechanism of plant dPCD. The dPCD process is tightly regulated by genetic networks and is involved in the transduction of signaling molecules. Several key regulators have been identified in diverse organisms and individual PCD events. However, complex molecular networks controlling plant dPCD remain highly elusive, and the original triggers of this process are still unknown. This review summarizes the recent progress on the transcriptional regulation and signaling of dPCD during vegetative and reproductive development. It is hoped that this review will provide an overall view of the molecular regulation of dPCD in different developmental processes in plants and identify specific mechanisms for regulating these dPCD events. In addition, the application of plants in industrial production can be improved by manipulating dPCD in specific processes, such as xylogenesis.

The transcription factor KNAT2/6b mediates changes in plant architecture in response to drought via down-regulating GA20ox1 in Populus alba × P. glandulosa

Plant architecture is genetically controlled, but is influenced by environmental factors. Plants have evolved adaptive mechanisms that allow changes in their architecture under stress, in which phytohormones play a central role. However, the gene regulators that connect growth and stress signals are rarely reported. Here, we report that a class I KNOX gene, PagKNAT2/6b, can directly inhibit the synthesis of gibberellin (GA), altering plant architecture and improving drought resistance in Populus. Expression of PagKNAT2/6b was significantly induced under drought conditions, and transgenic poplars overexpressing PagKNAT2/6b exhibited shorter internode length and smaller leaf size with short or even absent petioles. Interestingly, these transgenic plants showed improved drought resistance under both short- and long-term drought stress. Histological observations indicated that decreased internode length and leaf size were mainly caused by the inhibition of cell elongation and expansion. GA content was reduced, and the GA20-oxidase gene PagGA20ox1 was down-regulated in overexpressing plants. Expression of PagGA20ox1 was negatively related to that of PagKNAT2/6b under drought stress. ChIP and transient transcription activity assays revealed that PagGA20ox1 was directly targeted by PagKNAT2/6b. Therefore, this study provides evidence that PagKNAT2/6b mediates stress signals and changes in plant architecture via GA signaling by down-regulating PagGA20ox1.

WUSCHEL-related homeobox gene PagWOX11/12a is involved in drought tolerance through modulating reactive oxygen species scavenging in poplar

WUSCHEL-related homeobox (WOX) transcription factors play essential roles in key developmental processes and in response to different abiotic stresses. In a recent study, we have refined a molecular regulation mechanism that drought-induced PagERF35 directly activates the expression of PagWOX11/12a thus to promote root elongation and biomass, especially under drought conditions, and resulting in enhanced drought tolerance in poplar. In this study, we further found that PagWOX11/12a overexpression significantly enhanced drought tolerance and improved survival rate. Interestingly, transgenic poplars overexpressing PagWOX11/12a exhibited higher ability in scavenging reactive oxygen species (ROS) under drought stress. Combined with these and previous findings, we proposed the mechanism that PagWOX11/12a could not only promote root elongation and biomass growth to increase drought tolerance but also improve plant drought tolerance by regulating ROS level through possibly modulating the expression of ROS scavenging related genes.

Recent Advances in the Roles of HSFs and HSPs in Heat Stress Response in Woody Plants

A continuous increase in ambient temperature caused by global warming has been considered a worldwide threat. As sessile organisms, plants have evolved sophisticated heat shock response (HSR) to respond to elevated temperatures and other abiotic stresses, thereby minimizing damage and ensuring the protection of cellular homeostasis. In particular, for perennial trees, HSR is crucial for their long life cycle and development. HSR is a cell stress response that increases the number of chaperones including heat shock proteins (HSPs) to counter the negative effects on proteins caused by heat and other stresses. There are a large number of HSPs in plants, and their expression is directly regulated by a series of heat shock transcription factors (HSFs). Therefore, understanding the detailed molecular mechanisms of woody plants in response to extreme temperature is critical for exploring how woody species will be affected by climate changes. In this review article, we summarize the latest findings of the role of HSFs and HSPs in the HSR of woody species and discuss their regulatory networks and cross talk in HSR. In addition, strategies and programs for future research studies on the functions of HSFs and HSPs in the HSR of woody species are also proposed.

Evolutionary network genomics of wood formation in a phylogenetic survey of angiosperm forest trees

Wood formation was present in early angiosperms, but has been highly modified through evolution to generate the anatomical diversity seen in extant angiosperm lineages. In this project, we modeled changes in gene coexpression relationships associated with the evolution of wood formation in a phylogenetic survey of 13 angiosperm tree species. Gravitropic stimulation was used as an experimental treatment to alter wood formation and also perturb gene expression. Gene transcript abundances were determined using RNA sequencing of developing wood tissues from upright trees, and from the top (tension wood) and bottom (opposite wood) tissues of gravistimulated trees. A network-based approach was employed to align gene coexpression networks across species based on orthologous relationships. A large-scale, multilayer network was modeled that identified both lineage-specific gene coexpression modules and modules conserved across multiple species. Functional annotation and analysis of modules identified specific regulatory processes associated with conserved modules, including regulation of hormones, protein phosphorylation, meristem development and epigenetic processes. Our results provide novel insights into the evolution and development of wood formation, and demonstrate the ability to identify biological processes and genes important for the evolution of a foundational trait in nonmodel, undomesticated forest trees.

Characterization of poplar growth-regulating factors and analysis of their function in leaf size control

BACKGROUND

Growth-regulating factors (GRFs) are plant-specific transcription factors that control organ size. Nineteen GRF genes were identified in the Populus trichocarpa genome and one was reported to control leaf size mainly by regulating cell expansion. In this study, we further characterize the roles of the other poplar GRFs in leaf size control in a similar manner.

RESULTS

The 19 poplar GRF genes were clustered into six groups according to their phylogenetic relationship with Arabidopsis GRFs. Bioinformatic analysis, degradome, and transient transcription assays showed that 18 poplar GRFs were regulated by miR396, with GRF12b the only exception. The functions of PagGRF6b (Pag, Populus alba × P. glandulosa), PagGRF7a, PagGRF12a, and PagGRF12b, representing three different groups, were investigated. The results show that PagGRF6b may have no function on leaf size control, while PagGRF7a functions as a negative regulator of leaf size by regulating cell expansion. By contrast, PagGRF12a and PagGRF12b may function as positive regulators of leaf size control by regulating both cell proliferation and expansion, primarily cell proliferation.

CONCLUSIONS

The diversity of poplar GRFs in leaf size control may facilitate the specific, coordinated regulation of poplar leaf development through fine adjustment of cell proliferation and expansion.

WUSCHEL-related homeobox gene PagWOX11/12a responds to drought stress by enhancing root elongation and biomass growth in poplar

In plants, a large root system improves the uptake of water and nutrients, and is important for responding to drought stress. The poplar WUSCHEL-related homeobox (WOX) transcription factor promotes adventitious rooting, but its regulation of root growth in response to drought stress remains elusive. In this study, we found that PagWOX11/12a from hybrid poplar 84K (Populus alba×Populus glandulosa) is expressed predominantly in the roots and is strongly induced by drought stress. Compared with non-transgenic 84K plants, transgenic poplar plants overexpressing PagWOX11/12a displayed increased root biomass and enhanced drought tolerance, while opposite phenotypes were observed for PagWOX11/12a dominant repression plants. PagWOX11/12a functions as a nuclear transcriptional activator with a transactivation domain at the C-terminus. In addition, PagERF35 was found to specifically bind to a dehydration-responsive element (DRE) within the PagWOX11/12a promoter and activate PagWOX11/12a gene expression. These results indicate that PagERF35 may activate PagWOX11/12a expression in response to drought stress by promoting root elongation and biomass, thereby increasing drought tolerance of poplar.

KNAT2/6b, a class I KNOX gene, impedes xylem differentiation by regulating NAC domain transcription factors in poplar

Wood formation is the terminal differentiation of xylem mother cells derived from cambial initials, and negative regulators play important roles in xylem differentiation. The molecular mechanism of the negative regulator of xylem differentiation PagKNAT2/6b was investigated. PagKNAT2/6b is an ortholog of Arabidopsis KNAT2 and KNAT6 that is highly expressed in phloem and xylem. Compared to nontransgenic control plants, transgenic poplar plants overexpressing PagKNAT2/6b present with altered vascular patterns, characterized by decreased secondary xylem with thin cell walls containing less cellulose, xylose and lignin. RNA sequencing analyses revealed that differentially expressed genes are enriched in xylem differentiation and secondary wall synthesis functions. Expression of NAM/ATAF/CUC (NAC) domain genes including PagSND1-A1, PagSND1-A2, PagSND1-B2 and PagVND6-C1 is downregulated by PagKNAT2/6b, while PagXND1a is directly upregulated. Accordingly, the dominant repression form of PagKNAT2/6b leads to increased xylem width per stem diameter through downregulation of PagXND1a. PagKNAT2/6b can inhibit cell differentiation and secondary wall deposition during wood formation in poplar by modulating the expression of NAC domain transcription factors. Direct activation of PagXND1a by PagKNAT2/6b is a key node in the negative regulatory network of xylem differentiation by KNOXs.

Brassinosteroid regulation of wood formation in poplar

Brassinosteroids have been implicated in the differentiation of vascular cell types in herbaceous plants, but their roles during secondary growth and wood formation are not well defined. Here we pharmacologically and genetically manipulated brassinosteroid levels in poplar trees and assayed the effects on secondary growth and wood formation, and on gene expression within stems. Elevated brassinosteroid levels resulted in increases in secondary growth and tension wood formation, while inhibition of brassinosteroid synthesis resulted in decreased growth and secondary vascular differentiation. Analysis of gene expression showed that brassinosteroid action is positively associated with genes involved in cell differentiation and cell-wall biosynthesis. The results presented here show that brassinosteroids play a foundational role in the regulation of secondary growth and wood formation, in part through the regulation of cell differentiation and secondary cell wall biosynthesis.

[Circulating MicroRNA in diagnosis of nasopharyngeal carcinoma:a Meta-analysis]

Objective:To evaluate the diagnostic value of circulating microRNAs in nasopharyngeal carcinoma by Meta-analysis. Method:A number of databases in Chinese and English were searched, and the clinical studies published from the day the datebases were set up to July 2018 on detecting microRNAs as biomarkers in the diagnosis of nasopharyngeal carcinoma were collected. Literature selection, data extraction and literature quality evaluation were carried out according to the criteria of exclusion and inclusion.Then Meta-disc,Stata,and other softwares were used for the Meta-analysis. Result:Eighteen eligible articles were collected for systematic review, of which 7 independent case-control studies from 6 articles including 706 NPC patients and 353 controls were selected in the Meta-analysis. Since the obvious heterogeneity among the studies was observed,we conducted this Meta-analysis by the random effect model. The pool sensitivity, specificity, positive likelihood ratio, negative likelihood ratio and area under curve of circulating microRNAs in the diagnosis of nasopharyngeal carcinoma were 0.78（95%CI: 0.75-0.81, 0.81(95%CI: 0.77-0.85), 5.71(95%CI: 2.49-13.11), 0.23(95%CI: 0.13-0.42), 30.88(95%CI: 7.91-120.59) and 0.913 1,which illustrated the high diagnostic accuracy and significant clinical utility of microRNAs in the diagnosis of nasopharyngeal carcinoma.Subgroup analysis showed that the source of samples,the number of cases,the amount of the detecting microRNAs and the type of control groups were the main reasons contributing to the significant heterogeneity. Conclusion:MicroRNAs as biomarkers in the diagnosis of nasopharyngeal carcinoma possess significant potential value. .

[The expressions of CTLA-4 and PD-1 on CD(4)(+) T cells and the level of plasma VEGF in patients with obstructive sleep apnea hypopnea syndrome]

Objective: CD(4)(+)T cells, cytotoxic T-lymphocyte antigen 4 (CTLA-4), programmed cell death-1 (PD-1) and vascular endothelial growth factor (VEGF) are associated with cancer development. The aim of the present study was to investigate the expression of CTLA-4, PD-1 and VEGF in patients with obstructive sleep apnea hypopnea syndrome (OSAHS). Methods: From January 2017 to January 2018, a total of 47 first-visit outpatients were recruited in the Sleep and Respiratory Disorder Center of Guangdong Provincial People's Hospital, and were divided into control group (N=17, mean age 54±12 years), mild-to-moderate OSAHS group (N=15, mean age 54±12 years) and severe OSAHS group (N=15, mean age 56±13 years). Venous blood was collected, plasma and cells were isolated, the expressions of PD-1 and CTLA-4 on the surface of CD(4)(+)T cells were detected by flow cytometry, and plasma VEGF was measured by enzyme linked immunosorbent assay. Results: The proportion of CD(4)(+)T cells in control group, mild-to-moderate OSAHS group and severe OSAHS group were respectively(38±8)%, (35±8)% and (38±6)% (F=1.228, P>0.05). The expression of CTLA-4 on CD(4)(+)T cells were respectively [1.13 (0.59~1.78)]%, [0.45 (0.16~1.43)]% and [0.87(0.47~1.46)]% (H=2.205, P>0.05). The expression of PD-1 on CD(4)(+)T cells were respectively [4.24 (2.12~6.03)]%, [3.54(2.69~5.09)]% and [3.31(1.67~8.25)]% (H=0.541, P>0.05). The concentrations of VEGF in control group, mild-to-moderate OSAHS group and severe OSAHS group were statistically different [(395.16±87.78) ng/L vs (452.85±107.97) ng/L vs (546.42±199.27) ng/L, F=4.827, P=0.013]. Compared with the control group, VEGF concentration was significantly increased in the severe OSAHS group(P<0.01). VEGF concentration was correlated negatively with the lowest SpO(2) (r (s)=-0.480,P=0.001), but positively with apnea-hypopnea index(r (s)=0.403, P=0.005), oxygen desaturation index (r (s)=0.378, P=0.010) and proportion of SpO(2) less than or equal to 90% of total sleep time(r (s)=0.547, P=0.000 3). Conclusion: There was no significant difference of PD-1 and CTLA-4 expression on CD(4)(+)T cells in patients with and without OSAHS. The expression of VEGF was elevated in OSAHS patients, and increased with the severity of OSAHS and hypoxia.

Retraction Note to: An assessment of transgenomics as a tool for gene discovery in Populus euphratica Oliv

This article (Zhou et al. 2018) has been retracted by the authors because the sequence BIBAC 002A111F06 was incorrectly assigned to the wrong bacterial species. The BIBAC 002A111F06 sequence (GenBank Accession KC129717) reported in the paper was attributed to Populus euphratica Oliv. The BLAST search of this KC129717 sequence against the nr database at NCBI showed that it has very high similarity to a genomic sequence from the gram-negative bacteria Stenotrophomonas maltophilia. The bacterium associates with Populus euphratica Oliv. and DNA isolated from Populus euphratica Oliv. for the construction of the BIBAC clone library inlcuded DNA from Stenotrophomonas maltophilia. Therefore, the phenotype of the transgenic Arabidopsis line carrying the KC129717 sequence cannot be attributed to genes from Populus euphratica Oliv. The authors apologize for the confusion and misinterpretation of our data resulting from the incorrect sequence assignment. All authors agree to this retraction.

An assessment of transgenomics as a tool for gene discovery in Populus euphratica Oliv

Transgenomics for gene discovery in Populus euphratica. Transgenomics, a member of the omics family of methodologies, is characterized as the introduction of DNA from one organism into another on a genome-wide scale followed by the identification of recipients with altered phenotypes. This strategy allows investigators to identify the gene(s) involved in these phenotypic changes. It is particularly promising for woody plants that have a long life cycle and for which molecular tools are limited. In this study, we constructed a large-insert binary bacterial artificial chromosome library of Populus euphratica, a stress-tolerant poplar species, which included 55,296 clones with average insert sizes of about 127 kb. To date, 1077 of the clones have been transformed into Arabidopsis thaliana via Agrobacterium by the floral dip method. Of these, 69 transgenic lines showed phenotypic changes represented by diverse aspects of plant form and development, 22 of which were reproducibly associated with the same phenotypic change. One of the clones conferring transgenic plants with increased salt tolerance, 002A1F06, was further analyzed and the 127,284 bp insert in this clone harbored eight genes that have been previously reported to be involved in stress resistance. This study demonstrates that transgenomics is useful in the study of functional genomics of woody plants and in the identification of novel gene(s) responsible for economically important traits. Thus, transgenomics can also be used for validation of quantitative trait loci mapped by molecular markers.

Genomic risk variants at 3q22.3 are associated with keloids in a Chinese Han population

A keloid is the process of skin healing, collagen synthesis and metabolism of the loss of normal control in a sustained hyperactive state, resulting in excessive proliferation of collagen fibers. A large-scale genome-wide association study (GWAS) has identified multiple single nucleotide polymorphisms (SNPs) in the 3q22.3 loci that are associated with keloids in a Japanese population. However, the associations of SNPs in 3q22.3 with keloids were not confirmed in a selected Chinese population by a replication study. Thus, in the present study, the relationships between keloids and 3q22.3 were assessed in another independent Chinese Han population, including 309 keloid patients and 1080 control subjects. The results displayed that rs940187 was associated with keloids (OR=1.88, 95% CI 1.27-2.78, P=1.35E^-3) and remained significant after Bonferroni's correction for multiple testing, while rs1511412 showed only a trend association (OR=2.23, 95% CI 1.09-4.55, P=0.02) with keloids. In addition, we subsequently checked the annotation datasets for rs940187 with eQTLs and obtained two hits, trans-proteins SLC7A9 and LEMD3, with significant P values less than 1e-4. In summary, genomic risk variants at 3q22.3 are associated with keloids in a Chinese Han population and contribute to the development and deterioration of the keloids, together with environmental factors.

[Efficacy and safety of tiotropium Respimat in the treatment of chronic obstructive pulmonary disease: systematic review]

Objective: To evaluate the efficacy and safety of tiotropium Respimat in the treatment of chronic obstructive pulmonary disease (COPD) according to the Cochrane systematic evaluation. Methods: The Cochrane Library, PubMed, EMbase, CNKI, VIP and CBM, Wanfang Data were searched(from the foundation date to Jan. 2016) for the randomized controlled trials (RCTs) of tiotropium Respimat in the treatment of patients with COPD. Two reviewers independently retrieved the RCTs according to the inclusion and exclusion criteria, assessed the methodological quality of the included trials.and performed statistical analysis on the data using RevMan 5.3 software. Results: Totally 11 RCTs on efficacy were finally included.The results of the combined analysis showed that FEV(1) was significantly improved in the tiotropium Respimat group than that in the placebo group[MD=0.12, 95%CI(0.10-0.14), P<0.000 01], while FEV(1) was similar between the tiotropium Respimat group and the tiotropium HandiHaler group[5 μg: MD=0.00, 95%CI(-0.04-0.04), P=0.94; 2.5 μg: MD=-0.04, 95%CI(-0.10-0.01), P=0.12; 10 μg: MD=0.02, 95%CI(-0.06-0.09), P=0.66]. FVC was significantly improved in the tiotropium Respimat group than that in the placebo group[MD=0.18, 95%CI(0.09-0.28), P=0.0002], while FVC was similar between the tiotropium Respimat group and the HandiHaler group[2.5 μg: MD=-0.06, 95%CI(-0.16-0.04), P=0.24; 5 μg: MD=-0.00, 95%CI(-0.08-0.08), P=1.00; 10 μg: MD=0.02, 95%CI(-0.14-0.19), P=0.78]. The risk of acute exacerbations was lower in the tiotropium Respimat group (5 μg / kg) than in the placebo group [OR=0.72, 95%CI(0.60-0.86), P=0.000 3]. It was similar in the tiotropium Respimat group (5 μg) and the HandiHaler group[OR=1.01, 95%CI(0.94-1.09), P=0.71]. The SGRQ total score of the tiotropium Respimat group (5 μg) was significantly different from that of the placebo group[MD=-3.6, 95%CI(-3.88--3.32), P<0.000 01]. C(max, ss) and AUC(0-6 h, ss) were also similar between the tiotropium Respimat group and the HandiHaler group[MD=0.2, 95%CI(-5.1-5.5), P=0.94]; MD=-1.01, 95%CI(-11.78-9.77), P=0.85]. Nine RCTs were included in the evaluation of the incident rates of adverse drug reactions(ADR). There was no significant difference between the tiotropium Respimat group HandiHaler group and the placebo group[RR=0.95, 95%CI(0.89-1.00), P=0.05], [OR=1.07, 95%CI(1.00-1.16), P=0.06]. Conclusions: The efficacy and safety of tiotropium Respimat was similar to tiotropium HandiHaler in the treatment of COPD. They can effectively improve the pulmonary function and clinical symptoms of patients. But the long-term efficacy and safety of tiotropium Respimat still need to be confirmed by higher quality and larger RCTs with long-term follow-up.

Comparative Proteomic Analysis of Mature Pollen in Triploid and Diploid Populus deltoides

Ploidy affects plant growth vigor and cell size, but the relative effects of pollen fertility and allergenicity between triploid and diploid have not been systematically examined. Here we performed comparative analyses of fertility, proteome, and abundances of putative allergenic proteins of pollen in triploid poplar ‘ZhongHuai1’ (‘ZH1’, triploid) and ‘ZhongHuai2’ (‘ZH2’, diploid) generated from the same parents. The mature pollen was sterile in triploid poplar ‘ZH1’. By applying two-dimensional gel electrophoresis (2-DE), a total of 72 differentially expressed protein spots (DEPs) were detected in triploid poplar pollen. Among them, 24 upregulated and 43 downregulated proteins were identified in triploid poplar pollen using matrix-assisted laser desorption/ionisation coupled with time of-flight tandem mass spectrometer analysis (MALDI-TOF/TOF MS/MS). The main functions of these DEPs were related with “S-adenosylmethionine metabolism”, “actin cytoskeleton organization”, or “translational elongation”. The infertility of triploid poplar pollen might be related to its abnormal cytoskeletal system. In addition, the abundances of previously identified 28 putative allergenic proteins were compared among three poplar varieties (‘ZH1’, ‘ZH2’, and ‘2KEN8‘). Most putative allergenic proteins were downregulated in triploid poplar pollen. This work provides an insight into understanding the protein regulation mechanism of pollen infertility and low allergenicity in triploid poplar, and gives a clue to improving poplar polyploidy breeding and decreasing the pollen allergenicity.

NEDD4 single nucleotide polymorphism rs2271289 is associated with keloids in Chinese Han population

Keloids are abnormally raised fibroproliferative lesions that usually occur following cutaneous traumas. Recently, a large-scale genome-wide association study (GWAS) has identified multiple single nucleotide polymorphisms (SNPs) in three genetic loci that are associated with keloids in Japanese population. Subsequently, two reported loci 1q41 (rs873549 and rs1442440) and 15q21.3 (rs2271289) for keloids were confirmed in selected Chinese population. The association of these SNPs with clinical features of keloids, has not yet been studied. To explore the role of these SNPs in the pathogenesis of keloids, we performed a case-controlled study in another independent Chinese Han population to analyze the correlation between 4 SNPs (rs873549, rs2118610, rs1511412, rs2271289) and keloids phenotypes. 309 keloids patients and 1080 control subjects were included. The results showed that, in the dominant mode of inheritance, the minor allele T of SNP rs2271289 had significantly higher odd ratios (ORs) in the severe keloid group compared with both the controls and the mild keloid group. The ORs were maintained after Bonferroni's correction (OR: 4.09, 95% CI: 1.78-9.37, P-value 3.25E-04). The ratio of the severe: mild OR for rs2271289 (dominant model) is (4.73/1.84=2.57). Similar associations in SNP rs2271289 were seen for groups with no family history and multiplesite compared with the control groups. No associations between keloid number, family history or severity relative to the controls were observed for the other three SNPs. Our data support that rs2271289 is strongly associated with severe keloids and might contribute to the complexity of clinical features of keloids.

Proteomic analysis and candidate allergenic proteins in Populus deltoides CL. "2KEN8" mature pollen

Proteomic analysis was used to generate a map of Populus deltoides CL. "2KEN8" mature pollen proteins. By applying 2-D electrophoresis, we resolved 403 protein spots from mature pollen. Using the matrix-assisted laser desorption/ionization time time-of-flight/time-of-flight tandem mass spectrometry method, we identified 178 distinct proteins from 218 protein spots expressed in mature pollen. Moreover, out of these, 28 proteins were identified as putative allergens. The expression patterns of these putative allergen genes indicate that several of these genes are highly expressed in pollen. In addition, the members of profilin allergen family were analyzed and their expression patterns were compared with their homologous genes in Arabidopsis and rice. Knowledge of these identified allergens has the potential to improve specific diagnosis and allergen immunotherapy treatment for patients with poplar pollen allergy.

The heat shock factor gene family in Salix suchowensis: a genome-wide survey and expression profiling during development and abiotic stresses

Heat shock transcription factors (Hsfs), which act as important transcriptional regulatory proteins, play crucial roles in plant developmental processes, and stress responses. Recently, the genome of the shrub willow Salix suchowensis was fully sequenced. In this study, a total of 27 non-redundant Hsf genes were identified from the S. suchowensis genome. Phylogenetic analysis revealed that the members of the SsuHsf family can be divided into three groups (class A, B, and C) based on their structural characteristics. Promoter analysis indicated that the SsuHsfs promoters included various cis-acting elements related to hormone and/or stress responses. Furthermore, the expression profiles of 27 SsuHsfs were analyzed in different tissues and under various stresses (heat, drought, salt, and ABA treatment) using RT-PCR. The results demonstrated that the SsuHsfs were involved in abiotic stress responses. Our results contribute to a better understanding of the complexity of the SsuHsf gene family, and will facilitate functional characterization in future studies.

Evaluation of gene association methods for coexpression network construction and biological knowledge discovery

BACKGROUND

Constructing coexpression networks and performing network analysis using large-scale gene expression data sets is an effective way to uncover new biological knowledge; however, the methods used for gene association in constructing these coexpression networks have not been thoroughly evaluated. Since different methods lead to structurally different coexpression networks and provide different information, selecting the optimal gene association method is critical.

METHODS AND RESULTS

In this study, we compared eight gene association methods - Spearman rank correlation, Weighted Rank Correlation, Kendall, Hoeffding's D measure, Theil-Sen, Rank Theil-Sen, Distance Covariance, and Pearson - and focused on their true knowledge discovery rates in associating pathway genes and construction coordination networks of regulatory genes. We also examined the behaviors of different methods to microarray data with different properties, and whether the biological processes affect the efficiency of different methods.

CONCLUSIONS

We found that the Spearman, Hoeffding and Kendall methods are effective in identifying coexpressed pathway genes, whereas the Theil-sen, Rank Theil-Sen, Spearman, and Weighted Rank methods perform well in identifying coordinated transcription factors that control the same biological processes and traits. Surprisingly, the widely used Pearson method is generally less efficient, and so is the Distance Covariance method that can find gene pairs of multiple relationships. Some analyses we did clearly show Pearson and Distance Covariance methods have distinct behaviors as compared to all other six methods. The efficiencies of different methods vary with the data properties to some degree and are largely contingent upon the biological processes, which necessitates the pre-analysis to identify the best performing method for gene association and coexpression network construction.

The Ca2+ -dependent DNases are involved in secondary xylem development in Eucommia ulmoides

Secondary xylem development has long been recognized as a typical case of programmed cell death (PCD) in plants. During PCD, the degradation of genomic DNA is catalyzed by endonucleases. However, to date, no endonuclease has been shown to participate in secondary xylem development. Two novel Ca(2+) -dependent DNase genes, EuCaN1 and EuCaN2, were identified from the differentiating secondary xylem of the tree Eucommia ulmoides Oliv., their functions were studied by DNase activity assay, in situ hybridization, protein immunolocalization and virus-induced gene silencing experiments. Full-length cDNAs of EuCaN1 and EuCaN2 contained an open reading frame of 987 bp, encoding two proteins of 328 amino acids with SNase-like functional domains. The genomic DNA sequence for EuCaN1 had no introns, while EuCaN2 had 8 introns. EuCaN1 and EuCaN2 digested ssDNA and dsDNA with Ca(2+) -dependence at neutral pH. Their expression was confined to differentiating secondary xylem cells and the proteins were localized in the nucleus. Their activity dynamics was closely correlated with secondary xylem development. Secondary xylem cell differentiation is influenced by RNAi of endonuclease genes. The results provide evidence that the Ca(2+) -dependent DNases are involved in secondary xylem development.

Changes in freezing tolerance in hybrid poplar caused by up- and down-regulation of PtFAD2 gene expression

In plant species, the level of polyunsaturated fatty acids (PUFAs) is essential for cold acclimation. To test whether changes in PUFA levels can lead to the alteration of freezing tolerance in poplar trees, we up- and down-regulated a Populus tomentosa Delta-12 fatty acid desaturase gene (PtFAD2) in the hybrid poplar (P. alba x P. glandulosa) clone 84 K. Real-time PCR results demonstrated that compared to untransformed control lines, the transcriptional level of PtFAD2 increased by up to 90% in over-expressing poplar lines (line OE-1) and decreased in down-regulated RNAi lines by up to 64% (line DR-1). As a result, the content of linoleic (C18:2) and linolenic (C18:3) unsaturated fatty acids (FAs) in total FAs increased by 7.5 and 3.9%, respectively, in the OE-1 line and decreased by 14.4 and 5.4% in the DR-2 line when compared to non-transgenic lines. After freezing treatment at -4 degrees C for 3 h without pre-cold acclimation, the survival rates of the PtFAD2-over-expressing cuttings were significantly higher (60% for OE-1) than those of non-transgenic plants (36.7%) and down-regulated lines (10% for DR-2). These results clearly demonstrate that the expression level of PUFAs substantially affected the freezing tolerance of hybrid poplar cuttings and could thus be utilized as an effective strategy to improve poplar anti-freezing traits through genetic engineering biotechnology.

Dynamic changes in transcripts during regeneration of the secondary vascular system in Populus tomentosa Carr. revealed by cDNA microarrays

BACKGROUND

Wood is the end product of secondary vascular system development, which begins from the cambium. The wood formation process includes four major stages: cell expansion, secondary wall biosynthesis, lignification, and programmed cell death. Transcriptional profiling is a rapid way to screen for genes involved in these stages and their transitions, providing the basis for understanding the molecular mechanisms that control this process.

RESULTS

In this study, cDNA microarrays were prepared from a subtracted cDNA library (cambium zone versus leaf) of Chinese white poplar (Populus tomentosa Carr.) and employed to analyze the transcriptional profiles during the regeneration of the secondary vascular system, a platform established in our previous study. Two hundred and seven genes showed transcript-level differences at the different regeneration stages. Dramatic transcriptional changes were observed at cambium initiation, cambium formation and differentiation, and xylem development, suggesting that these up- or downregulated genes play important roles in these stage transitions. Transcription factors such as AUX/IAA and PINHEAD, which were previously shown to be involved in meristem and vascular tissue differentiation, were strongly transcribed at the stages when cambial cells were initiated and underwent differentiation, whereas genes encoding MYB proteins and several small heat shock proteins were strongly transcribed at the stage when xylem development begins.

CONCLUSION

Employing this method, we observed dynamic changes in gene transcript levels at the key stages, including cambium initiation, cambium formation and differentiation, and xylem development, suggesting that these up- or downregulated genes are strongly involved in these stage transitions. Further studies of these genes could help elucidate their roles in wood formation.

[Development of nano-scale genic carriers in biomedicine]

Nano biotechnology is a developing field of science and technology in the 21st century. The emergence of nanomaterials provides a new way for gene carriers. This paper demonstrates the advantages and types of nano-scale genic carriers and the methods for introducing it into the body, and reviewed the application of nano-scale genic carriers in gene therapy and in breeding.

Regeneration of the secondary vascular system in poplar as a novel system to investigate gene expression by a proteomic approach

Wood formation is a complex process composing many biological events. To access its key developmental stages, we have established a regeneration system that can mimic the initiation and differentiation of cambium cells for Chinese white poplar. Anatomical studies showed that new cambium and xylem re-appeared in sequence within a few weeks after being debarked. This provides the opportunity to follow key stages of wood formation by sampling clonal trees at different regeneration times. We used this system in combination with a proteomic approach to analyze proteins expressed in different regeneration stages. PMFs for 244 proteins differentially displayed were obtained and queried against public databases. Putative functions of 199 of these proteins were assigned and classified. Regulatory genes for cell cycle progression, differentiation and cell fate were expressed in the formation of cambial tissue, while 27 genes involved in secondary wall formation were predominantly found in the xylem developing stage. This indicates that the change of gene expression pattern is corresponding to the progression of second vascular system regeneration when and where the key events of wood development occur. Further exploration of these interesting genes may provide insight into the molecular mechanisms of wood formation.

The cry3Aa gene of Bacillus thuringiensis Bt886 encodes a toxin against long-horned beetles

This report describes the identification of a new toxigenic strain of Bacillus thuringiensis specific for long-horned beetles. B. thuringiensis Bt866 encodes a cry3Aa-like gene (Bt886cry3Aa) that is 1,956 bp in length and is predicted to encode an 85.78-kDa protein. The gene is highly similar to cry3Aa1, differing in only six nucleotides and four amino acids. The four disparate amino acids occur within the conserved domains of the Cry3Aa toxin. The expression of Bt866cry3A in Escherichia coli cells resulted in a high level of toxicity toward Apriona germari Hope larvae. More than 75% of the larvae were killed; and the remaining survivors exhibited slower growth. These results indicate that the toxigenic strain Bt886cry3Aa encodes a protein that is specific against long-horned beetles. Genetic engineering of the Bt866cry3Aa gene into poplar plantations may provide resistance to long-horned beetles.

Cell encapsulation with alginate and alpha-phenoxycinnamylidene-acetylated poly(allylamine)

In general, microcapsules prepared from alginate and polycations lack mechanical strength because the interaction between alginate and polycations is ionic instead of covalent, which represents a much stronger bond. To increase the mechanical strength of the capsule, we prepared photosensitive microcapsules that could form covalent bonds between polymers in the capsular membrane by light irradiation. Two types of photosensitive poly(allylamine), with 5% and 10% of amino groups modified by alpha-phenoxycinnamylidene acetylchloride, were synthesized. Both photopolymers exhibited an absorption maximum at 325 nm and were capable of crosslinking upon light exposure. These photosensitive polymers were used for the preparation of microcapsules. The capsules formed from this photosensitive poly(allylamine) and alginate were strengthened significantly by light irradiation. Only 28% of the microcapsules prepared from the 5%-modified photopolymer fractured after 48 h of shaking at 150 rpm. This fracture percentage is much lower when compared with the 60% of capsules fractured when prepared from the untreated poly(allylamine). By using poly(allylamine) at 10% modification, the mechanical strength was improved only slightly, with 26% of capsules fractured. Analysis of the permeability test indicated that the photo-crosslinked capsular membrane was freely permeable to cytochrome c and myoglobin, but less permeable to serum albumin. The encapsulation method was used to entrap and culture IW32 mouse leukemia cells. The cells proliferated to a density of about 1.1 x 10(7) cells/mL in the capsules after 7 days of cultivation. Concurrently, the concentration of erythropoietin in the microcapsules increased to 800 mU/mL. This new encapsulation technique has great potential in the application of a bioindustrial cell-culturing process.

A novel cell encapsulation method using photosensitive poly(allylamine alpha-cyanocinnamylideneacetate)

A photosensitive alpha-cyanocinnamylideneacetyl group was coupled to poly(allylamine) to obtain a photosensitive polymer. This photosensitive poly(allylamine alpha-cyanocinnamylideneacetate) can cross-link upon light exposure. Microcapsules were fabricated from alginate in contact with Ca+2 ion, followed by coating with the photosensitive poly(allylamine alpha-cyanocinnamylideneacetate). The microcapsules, thus formed, can be strengthened significantly by the light-induced cross-linking of poly(allylamine alpha-cyanocinnamylideneacetate). Only 16 capsules (out of 50) prepared from the photosensitive poly(allylamine alpha-cyanocinnamylideneacetate) fractured after 48 h of agitation. For microcapsules prepared from the unmodified poly(allylamine), 32 capsules fractured. The photo cross-linked capsular membrane was permeable to cytochrome C, moderately permeable to myoglobin, and least permeable to serum albumin. IW32 (a mouse leukaemia cell line) cells were entrapped and cultured within these microcapsules. The cells proliferated to a density of about 9 x 10(6) cells/ml in the capsules after 7 days of cultivation.