Genome-wide identification and expression pattern analysis of MIKC-Type MADS-box genes in Chionanthus retusus, an androdioecy plant.

BACKGROUND: The MADS-box gene family is widely distributed in the plant kingdom, and its members typically encoding transcription factors to regulate various aspects of plant growth and development. In particular, the MIKC-type MADS-box genes play a crucial role in the determination of floral organ development and identity recognition. As a type of androdioecy plant, Chionanthus retusus have unique gender differentiation. Manifested as male individuals with only male flowers and female individuals with only bisexual flowers. However, due to the lack of reference genome information, the characteristics of MIKC-type MADS-box genes in C. retusus and its role in gender differentiation of C. retusus remain largely unknown. Therefore, it is necessary to identify and characterize the MADS-box gene family within the genome of the C. retusus. RESULTS: In this study, we performed a genome-wide identification and analysis of MIKC-type MADS-box genes in C. retusus (2n = 2x = 46), utilizing the latest reference genome, and studied its expression pattern in individuals of different genders. As a result, we identified a total of 61 MIKC-type MADS-box genes in C. retusus. 61 MIKC-type MADS-box genes can be divided into 12 subfamilies and distributed on 18 chromosomes. Genome collinearity analysis revealed their conservation in evolution, while gene structure, domains and motif analysis indicated their conservation in structure. Finally, based on their expression patterns in floral organs of different sexes, we have identified that CrMADS45 and CrMADS60 may potentially be involved in the gender differentiation of C. retusus. CONCLUSIONS: Our studies have provided a general understanding of the conservation and characteristics of the MIKC-type MADS-box genes family in C. retusus. And it has been demonstrated that members of the AG subfamily, CrMADS45 and CrMADS60, may play important roles in the gender differentiation of C. retusus. This provides a reference for future breeding efforts to improve flower types in C. retusus and further investigate the role of MIKC-type MADS-box genes in gender differentiation.

Transcriptomic and free monoterpene analyses of aroma reveal that isopentenyl diphosphate isomerase inhibits monoterpene biosynthesis in grape (Vitis vinifera L.).

BACKGROUND: Monoterpenes are among the most important volatile aromatic compounds contributing to the flavor and aroma of grapes and wine. However, the molecular basis of monoterpene biosynthesis has not yet been fully elucidated. RESULTS: In our study, transcriptomics and gas chromatography-mass spectrometry (GC-MS) were used to mine candidate genes and transcription factors involved in monoterpene biosynthesis between high-monoterpene and zero-monoterpene table grape cultivars. We found that monoterpene biosynthesis was positively correlated by the expression of five genes encoding 1-deoxy-D-xylulose-5-phosphate synthase (VvDXSs), one encoding 4-hydroxy-3-methylbut-2-enyl diphosphate reductase (VvHDR), three hydroxy-3-methylglutaryl-CoA synthases (VvHMGSs) and one mevalonate kinase (VvMVK), whereas the expression of one isopentenyl diphosphate isomerase (VvIDI) and one 3-hydroxy-3-methylglutaryl-CoA reductase (VvHMGR) negatively correlated monoterpene biosynthesis. Of these genes, VvIDI was selected to validate its function in monoterpene accumulation through a transient overexpression experiment, and was shown to inhibit the biosynthesis of grape linalool and α-terpineol. Meanwhile, we found that a 64-amino acid extension sequence at the N-terminus can guide the VvIDI protein to target the chloroplast. CONCLUSIONS: The findings of this study should help to guide future functional analysis of key genes as well as mining the potential regulatory mechanism of monoterpene biosynthesis in grapes and grape products.

Regulation of Disease-Resistance Genes against CWMV Infection by NbHAG1-Mediated H3K36ac.

Post-translational modification of proteins plays a critical role in plant-pathogen interactions. Here, we demonstrate in Nicotiana benthamiana that knockout of NbHAG1 promotes Chinese wheat mosaic virus (CWMV) infection, whereas NbHAG1 overexpression inhibits infection. Transcriptome sequencing indicated that a series of disease resistance-related genes were up-regulated after overexpression of NbHAG1. In addition, cleavage under targets and tagmentation (Cut&Tag)-qPCR results demonstrated that NbHAG1 may activate the transcription of its downstream disease-resistance genes by facilitating the acetylation level of H3K36ac. Therefore, we suggest that NbHAG1 is an important positive regulator of resistance to CWMV infestation.

Genome-wide identification and analysis of the SUPPRESSOR of MAX2 1-LIKE gene family and its interaction with DWARF14 in poplar.

BACKGROUND: Strigolactones (SLs) are important phytohormones that can regulate branch development in plants. Although SUPPRESSOR of MAX2 1-LIKE proteins (SMXLs) play a crucial role in SL signaling transduction, the SMXL gene family has not been well characterized in poplar. RESULTS: In this study, 12 members of the poplar SMXL gene family were identified and phylogenetically classified into four clades. Motif and 3D structural analyses revealed that PtSMXL proteins are structurally very conserved; however, the P-loop NTPase domain at the C-terminal was found to vary substantially among clades. A genomic collinearity analysis indicated that PtSMXL gene family members have expanded during recent genome doubling events in poplar, with all gene pairs subsequently undergoing purifying selection. According to a Cis-element analysis, PtSMXL promoters contain many light-responsive elements. In an expression pattern analysis, all 12 PtSMXL genes displayed tissue-specific expression, especially PtSMXL8a. PtSMXL7b expression was significantly downregulated after axillary bud growth begins. In addition, the expressions of PtSMXL7b and PtSMXL8a were highly induced by 2 µM GR24, a synthetic SL analog, thus suggesting that these genes are involved in SL-regulated axillary bud growth. In a yeast two-hybrid assay, only PtSMXL7b in clade II was able to interact with the SL receptor PtD14a in an SL dependent manner, which indicates that PtSMXL7b may be the functional homolog of D53/SMXL6/7/8 in poplar. Finally, we established its ability to affect axillary bud growth by constructing poplar overexpressing the PtSMXL7b gene. CONCLUSIONS: Our findings may inform future research on the functions of SMXLs in poplar, especially with respect to branch development.

Source Contributions to PM2.5-Related Mortality and Costs: Evidence for Emission Allocation and Compensation Strategies in China.

The emissions from various pollution sources were not proportional to their contributions to ambient PM2.5 concentrations and associated health burdens. That means even with the same total abatement targets, different abatement allocation strategies across emission sources can have distinct health benefits. Insufficient knowledge of various sources' contributions to health burdens in China, the country suffering substantial PM2.5-related deaths, hindered the government from seeking optimized abatement allocation strategies. In this context, we separated the contributions of 155 emission sources (31 provinces × 5 sectors) to PM2.5-related mortality across China in 2017 by coupling the Comprehensive Air Quality Model with Extensions (CAMx), Weather Research and Forecasting model (WRF), and health impact assessment model. We further identified the priority-control emission sources and quantified interprovincial ecological compensation volumes to alleviate inequality induced by emission allocation strategies. Results showed that PM2.5 pollution caused 899,443 excess deaths and around 127 billion USD costs in 2017. Approximately half of the deaths and costs were attributable to emissions from sources outside the boundary of the regions where the deaths occurred. Twenty-five out of 155 emission sources that contributed to the top 60% mortality burdens and had high marginal abatement efficiencies in China shall be the priority-control emission sources. A 1 µg/m3 decrease of PM2.5 concentration in regions where these key emission sources occur shall be compensated by 76-153 million USD in their receptor regions. Our study sheds light on the sources' contributions to mortality burdens and costs and provides scientific evidence for optimizing the emission allocation and compensation strategies in China. It also has wide implications for other countries suffering similar problems.

Large Virtual Transboundary Hazardous Waste Flows: The Case of China.

The Basel Convention and prior studies mainly focused on the physical transboundary movements of hazardous waste (transporting waste from one region to another for cheaper disposal). Here, we take China, the world's largest waste producer, as an example and reveal the virtual hazardous waste flows in trade (outsourcing waste by importing waste-intensive products) by developing a multiregional input-output model. Our model characterizes the impact of international trade between China and 140 economies and China's interprovincial trade on hazardous waste generated by 161,599 Chinese enterprises. We find that, in 2015, virtual hazardous waste flows in China's trade reached 26.6 million tons (67% of the national total), of which 31% were generated during the production of goods that were ultimately consumed abroad. Trade-related production is much dirtier than locally consumed production, generating 26% more hazardous waste per unit of GDP. Under the impact of virtual flows, 40% of the waste-intensive production and relevant disposal duty is unequally concentrated in three Chinese provinces (including two least-developed ones, Qinghai and Xinjiang). Our findings imply the importance of expanding the scope of transboundary waste regulations and provide a quantitative basis for introducing consumer responsibilities. This may help relieve waste management burdens in less-developed "waste havens".

Co-drivers of Air Pollutant and CO2 Emissions from On-Road Transportation in China 2010-2020.

Co-controlling the emissions of air pollutants and CO2 from automobiles is crucial for addressing the intertwined challenges of air pollution and climate change in China. Here, we analyze the synergetic characteristics of air pollutant and CO2 emissions from China's on-road transportation and identify the co-drivers influencing these trends. Using detailed emission inventories and employing index decomposition analysis, we found that despite notable progress in pollution control, minimizing on-road CO2 emissions remains a formidable task. Over 2010-2020, the estimated sectoral emissions of VOCs, NOx, PM2.5, and CO declined by 49.9%, 25.9%, 75.2%, and 63.5%, respectively, while CO2 emissions increased by 46.1%. Light-duty passenger vehicles and heavy-duty trucks have been identified as the primary contributors to carbon-pollution co-emissions, highlighting the need for tailored policies. The driver analysis indicates that socioeconomic changes are primary drivers of emission growth, while policy controls, particularly advances in emission efficiency, can facilitate co-reductions. Regional disparities emphasize the need for policy refinement, including reducing dependency on fuel vehicles in the passenger subsector and prioritizing co-reduction strategies in high-emission provinces in the freight subsector. Overall, our study confirms the effectiveness of China's on-road control policies and provides valuable insights for future policy makers in China and other similarly positioned developing countries.

Closing the Gap between Carbon Neutrality Targets and Action: Technology Solutions for China's Key Energy-Intensive Sectors.

Facing significant carbon emissions annually, China requires a clear decarbonization strategy to meet its climate targets. This study presents a MESSAGEix-CAEP model to explore Chinese decarbonization pathways and their cost-benefit under two mitigation scenarios by establishing connections between five energy-intensive sectors based on energy and material flows. The results indicated the following: 1) Interaction and feedback between sectors should not be disregarded. The electrification process of the other four sectors was projected to increase electricity production by 206%, resulting in a higher power demand than current forecasts. 2) The marginal abatement cost to achieve carbon neutrality across all five sectors was 2189 CNY/tCO2, notably higher than current Chinese carbon emission trading prices. 3) The cost-benefit analysis indicates that a more ambitious abatement strategy would decrease the marginal abatement cost and result in a higher net carbon abatement benefit. The cumulative net benefit of carbon reduction was 7.8 trillion CNY under ambitious mitigation scenario, 1.3 trillion CNY higher than that under current Chinese mitigation scenario. These findings suggest that policy-makers should focus on the interaction effects of decarbonization pathways between sectors and strengthen their decarbonization efforts to motivate early carbon reduction.

Spatio-temporal evolution and influencing factors of synergizing the reduction of pollution and carbon emissions - Utilizing multi-source remote sensing data and GTWR model.

Grasping current circumstances and influencing components of the synergistic degree regarding reducing pollution and carbon has been recognized as a crucial part of China in response to the protection of the environment and climate mitigation. With the introduction of remote sensing night-time light, CO2 emissions at multi-scale have been estimated in this study. Accordingly, an upward trend of "CO2-PM2.5" synergistic reduction was discovered, which was indicated by an increase of 78.18% regarding the index constructed of 358 cities in China from 2014 to 2020. Additionally, it has been confirmed that the reduction in pollution and carbon emissions could coordinate with economic growth indirectly. Lastly, it has identified the spatial discrepancy of influencing factors and the results have emphasized the rebound effect of technological progress and industrial upgrades, whilst the development of clean energy can offset the increase in energy consumption thus contributing to the synergy of pollution and carbon reduction. Moreover, it has been highlighted that environmental background, industrial structure, and socio-economic characteristics of different cities should be considered comprehensively in order to better achieve the goals of "Beautiful China" and "Carbon Neutrality".

Comparative analysis of visual amenity services valuation: A nationwide assessment through propensity scoring matching and hedonic regression.

Conventional hedonic valuations of environmental amenities and cultural ecosystem services (CES) expose two limitations. First, related studies are unable to fully capture the value of visual amenity services which synergistically contribute and enhance the provision of valuable CES together with recreation, educational and spiritual services. Second, studies using linear hedonic regression cannot address potential bias resulting from multicollinearity in independent variables. We found that popular choices of covariates are correlated with the main amenity variable, which can lead to an undermined estimation precision. Therefore, to address those shortcomings, we first employed a specific proxy dummy variable to assign treatment and control individuals based on the service type. Second, we adopted propensity score matching (PSM) methodology to match treatment and control observations conditional on overlapping baseline covariates in order to avoid collinearity. Then, we carried out a comparative evaluation of a nationwide visual amenity service of the ocean ecosystem in China, via our new PSM-based average treatment effects (ATE) methodology and a conventional linear hedonic regression. Two methodologies showed opposite results, with an 8.3% premium in apartment price via PSM-ATE and a negative 0.9% premium via hedonic linear regression. Via a novel evaluation method and a nationwide case study, we conclude that diversifying and enriching the current methodology should be the priority for environmental amenity and cultural ecosystem services-related valuations.

One-dimensional consolidation of highly saturated abandoned-soil under time-dependent stress: An analytical study.

A thorough knowledge of the consolidation behavior of highly saturated soil under time-dependent stress is essential for the design and construction of abandoned-soil dump sites in the soft soil regions of China. In this study, one-dimensional consolidation analytical solutions are derived for such soil under one-way and two-way drainage conditions, accommodating the time-dependent stress created by various dumping protocols. Representative soil samples are obtained, and consolidation tests are conducted with various saturation degrees (one-way drainage) and loading protocols (two-way drainage), to verify the consolidation equation and determine its range of applicability to various saturation degrees. The effects of layer thickness, dumping type, and compaction degree on the consolidation behaviors of highly saturated abandoned-soil dumps are investigated. The one-dimensional consolidation equation is applicable to soil with saturation degree not lower than 75% under instantaneous stress, stepped stress, and linear stress. The pore pressure distribution with depth is not symmetrical; the eccentric distance of consolidation degree increases with increasing layer thickness in the stress application stage and is approximately zero in the stress keeping stage. The pore pressure at middle of the soil layer increases with increasing layer thickness and decreases with increasing dumping rate from the completion of soil dumping. With increasing compaction degree, the middle pore pressure increases, while the surface settlement decreases. In the premise of the stability of an abandoned-soil dump, where the goals are to reduce post-construction settlement and to shorten the consolidation process of the entire soil layer, the important factors are smaller layer thickness, higher dumping rate, and larger compaction degree.

Mitigating China's Ozone Pollution with More Balanced Health Benefits.

China is confronting the challenge of opposite health benefits (OHBs) during ambient ozone (O3) mitigation because the same reduction scheme might yield opposite impacts on O3 levels and associated public health across different regions. Here, we used a combination of chemical transport modeling, health benefit assessments, and machine learning to capture such OHBs and optimize O3 mitigation pathways based on 121 control scenarios. We revealed that, for the China mainland, Beijing-Tianjin-Hebei and its surroundings ("2 + 26" cities), Yangtze River Delta, and Pearl River Delta, there could be at most 2897, 920, 1247, and 896 additional O3-related deaths in urban areas, respectively, accompanying 21,512, 3442, 5614, and 642 avoided O3-related deaths in rural areas, respectively, at the same control stage. Additionally, potential disbenefits during O3 mitigation were "pro-wealthy", that is, residents in developed regions are more likely to afford additional health risks. In order to avoid OHBs during O3 abatement, we proposed a two-phase control strategy, whereby the reduction ratio of NOX (nitrogen oxide) to VOCs (volatile organic compounds) was adjusted according to health benefit distribution patterns. Our study provided novel insights into China's O3 attainment and references for other countries facing the dual challenges of environmental pollution and associated inequality issues.

Interaction Patterns between Climate Action and Air Cleaning in China: A Two-Way Evaluation Based on an Ensemble Learning Approach.

China will attempt to achieve its simultaneous goals in 2060, whereby carbon neutrality will be accomplished and the PM2.5 (fine particulate matter) level is expected to remain below 10 µg/m3. Identifying interaction patterns between air cleaning and climate action represents an important step to obtain cobenefits. Here, we used a random sampling strategy through the combination of chemical transport modeling and machine learning approach to capture the interaction effects from two perspectives in which the driving forces of both climate action and air cleaning measures were compared. We revealed that climate action where carbon emissions were decreased to 1.9 Bt (billion tons) could lead to a PM2.5 level of 12.4 µg/m3 (95% CI (confidence interval): 10.2-14.6 µg/m3) in 2060, while air cleaning could force carbon emissions to reach 1.93 Bt (95% CI: 0.79-3.19 Bt) to achieve net carbon neutrality based on the potential carbon sinks in 2060. Additional controls targeting primary PM2.5, ammonia, and volatile organic compounds were required as supplements to overcome the partial lack of climate action. Our study provides novel insights into the cobenefits of air-quality improvement and climate change mitigation, indicating that the effect of air cleaning on the simultaneous goals might have been underestimated before.

Drivers of improved PM2.5 air quality in China from 2013 to 2017.

From 2013 to 2017, with the implementation of the toughest-ever clean air policy in China, significant declines in fine particle (PM2.5) concentrations occurred nationwide. Here we estimate the drivers of the improved PM2.5 air quality and the associated health benefits in China from 2013 to 2017 based on a measure-specific integrated evaluation approach, which combines a bottom-up emission inventory, a chemical transport model, and epidemiological exposure-response functions. The estimated national population-weighted annual mean PM2.5 concentrations decreased from 61.8 (95%CI: 53.3-70.0) to 42.0 µg/m3 (95% CI: 35.7-48.6) in 5 y, with dominant contributions from anthropogenic emission abatements. Although interannual meteorological variations could significantly alter PM2.5 concentrations, the corresponding effects on the 5-y trends were relatively small. The measure-by-measure evaluation indicated that strengthening industrial emission standards (power plants and emission-intensive industrial sectors), upgrades on industrial boilers, phasing out outdated industrial capacities, and promoting clean fuels in the residential sector were major effective measures in reducing PM2.5 pollution and health burdens. These measures were estimated to contribute to 6.6- (95% CI: 5.9-7.1), 4.4- (95% CI: 3.8-4.9), 2.8- (95% CI: 2.5-3.0), and 2.2- (95% CI: 2.0-2.5) µg/m3 declines in the national PM2.5 concentration in 2017, respectively, and further reduced PM2.5-attributable excess deaths by 0.37 million (95% CI: 0.35-0.39), or 92% of the total avoided deaths. Our study confirms the effectiveness of China's recent clean air actions, and the measure-by-measure evaluation provides insights into future clean air policy making in China and in other developing and polluting countries.

Identification of heavy metal leaching patterns in municipal solid waste incineration fly ash based on an explainable machine learning approach.

The leaching risk of heavy metal (HM) in municipal solid waste incineration fly ash (MSWI-FA) leads to a big challenge for FA landfilling. In this work, the HM leaching patterns were identified via 6 highly available indices of FA, in which 160 stabilized FA samples were collected from 4 incineration plants in eastern China and an explainable machine learning approach based on boosting and game analysis was conducted to assess the leaching potentials of 6 HMs (Cr, Cd, Cu, Ni, Pb and Zn). We found that, there remained high exceeding risks of Cd and Pb in stabilized FA. In addition, the S-Cl (soluble chlorine) content was the most influential factor of the leaching behaviors of Cd, Cu, Pb and Zn, more important than pH in regard to Cu, Pb and Zn. We quantified the influence of S-Cl on the HM leaching of Cd, Cu, Pb and Zn, whereby their leaching concentrations would increase by 223.5%, 215.2%, 216.5% and 222.6%, respectively, for every 0.5 mol/L order increase in S-Cl concentration. Finally, a fast determination criterion for the FA landfill was proposed, that is, FA of which S-Cl was less than 0.412 mol/L was acceptable.

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.

A comprehensive study on emission of volatile organic compounds for light duty gasoline passenger vehicles in China: Illustration of impact factors and renewal emissions of major compounds.

BACKGROUND: Many volatile organic compounds (VOCs) are efficient precursors for both ozone and secondary organic aerosol (SOA) which are problematic to environmental controls in many global cities. Vehicle emission is one of the most important anthropogenic sources for VOCs. In between, light duty gasoline passenger vehicles (LDGPVs) contributed more than half of the on-road vehicles in China, demonstrating unique emission characteristics and also significant contributions in emission inventory. OBJECTIVES: To illustrate the variation of VOCs emissions from LDGPVs under different conditions, evaluate the sensitivity of the potential influencing factors, such as emission standards, displacement, cumulative mileage, and driving mode, on the VOCs emissions profiles, and to update the emission inventory by taking into account of the most influential factor. METHODS: In this study, seventy-four in-used LDGPVs were examined by the chassis dynamometer. A total of 25 VOCs in the emissions was quantified using an online time of flight mass spectrometer (TOF-MS). Fuel-based emission factors (EF) were calculated. RESULTS: The results showed that the maximum ΣEF (260.4 ± 241.1 mg/L) was seen for LDGPVs at a high acceleration rate (0.9 m/s2). From the technical control emission standard aspect, the total emission factor of VOCs (expressed as ∑EF) was declined for China IV LDGPVs relative to China III vehicles, with the decreasing extent determined as 24.8%. Among LDGPVs with engine capacity of <1.5 L, 1.5-2.5 L and >2.5 L, it is for 1.5-2.5 L that the lowest ∑EF (101.2 ± 70.1 mg/L) was determined. Along with the increasing of cumulative mileage, the EF values of VOCs were uplift, and the ∑VOCs increased almost linearity, while the increasing trend became steady for ∑EF when the cumulative mileage more than 8 × 104 km. As for different driving conditions, the sequence of EFs from high to low are presented as acceleration (239.3 ± 203.5 mg/L) >idle (226.1 ± 195.6 mg/L) >deceleration (218.5 ± 193.1 mg/L)>uniform (218.2 ± 182.5 mg/L)>slide (176.1 ± 165.2 mg/L). While the cruising speeds increased between 15 and 50 km/h, the linearity between ΣEF declined; however, an opposite trend was seen when the acceleration rates increased. In the chemical speciation, the reactive aromatics contributed the largest fraction of the VOCs (>40%). The ratio of benzene to toluene (B/T) was loaded in high interval (0.94-1.33) in this paper. Larger fluctuation of coefficient of variation (CV) was found among different cumulative mileage and displacement. By taking into account the deterioration effect related to cumulative mileage, emissions of butene, pentene, benzene and toluene were 42.9 Gg, 49.7 Gg, 109.6 Gg and 51.9 Gg in respect for LDGPVs that composed of China III and China IV. CONCLUSIONS: Our results demonstrated the necessaries in upgrading the emission control technology. Cumulative mileages and displacements are the two most dominated factors that impacted on the EFs and chemical profiles of VOCs. The higher emission of benzene estimated demonstrated the possible elevation of VOCs in comparison with previous studies.

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.

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.

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.