Allelic variation in transcription factor PtoWRKY68 contributes to drought tolerance in Populus.

Drought stress limits woody species productivity and influences tree distribution. However, dissecting the molecular mechanisms that underpin drought responses in forest trees can be challenging due to trait complexity. Here, using a panel of 300 Chinese white poplar (Populus tomentosa) accessions collected from different geographical climatic regions in China, we performed a genome-wide association study (GWAS) on seven drought-related traits and identified PtoWRKY68 as a candidate gene involved in the response to drought stress. A 12-bp insertion and/or deletion and three nonsynonymous variants in the PtoWRKY68 coding sequence categorized natural populations of P. tomentosa into two haplotype groups, PtoWRKY68hap1 and PtoWRKY68hap2. The allelic variation in these two PtoWRKY68 haplotypes conferred differential transcriptional regulatory activities and binding to the promoters of downstream abscisic acid (ABA) efflux and signaling genes. Overexpression of PtoWRKY68hap1 and PtoWRKY68hap2 in Arabidopsis (Arabidopsis thaliana) ameliorated the drought tolerance of two transgenic lines and increased ABA content by 42.7% and 14.3% compared to wild-type plants, respectively. Notably, PtoWRKY68hap1 (associated with drought tolerance) is ubiquitous in accessions in water-deficient environments, whereas the drought-sensitive allele PtoWRKY68hap2 is widely distributed in well-watered regions, consistent with the trends in local precipitation, suggesting that these alleles correspond to geographical adaptation in Populus. Moreover, quantitative trait loci analysis and an electrophoretic mobility shift assay showed that SHORT VEGETATIVE PHASE (PtoSVP.3) positively regulates the expression of PtoWRKY68 under drought stress. We propose a drought tolerance regulatory module in which PtoWRKY68 modulates ABA signaling and accumulation, providing insight into the genetic basis of drought tolerance in trees. Our findings will facilitate molecular breeding to improve the drought tolerance of forest trees.

Ba6RE2Ti4O17 (RE = Nd, Sm, Gd, Dy-Yb): A Family of Rare-Earth-Based Layered Triangular Lattice Magnets.

The exploration of new rare-earth (RE)-based triangular-lattice materials plays a significant role in motivating the discovery of exotic magnetic states. Herein, we report a family of hexagonal perovskite compounds Ba6RE2Ti4O17 (RE = Nd, Sm, Gd, Dy-Yb) with a space group of P63/mmc, where magnetic RE3+ ions are distributed on the parallel triangular-lattice layers within the ab-plane and stacked in an 'AA'-type fashion along the c-axis. The low-temperature magnetic characterizations indicate that all synthesized Ba6RE2Ti4O17 compounds exhibit dominant antiferromagnetic (AFM) interactions and the absence of magnetic order down to 1.8 K. The isothermal magnetization and electron spin resonance results reveal the distinct magnetic anisotropy for the compounds with different RE ions. Moreover, the as-grown Ba6Nd2Ti4O17 single crystals exhibit Ising-like magnetic anisotropy with a magnetic easy-axis perpendicular to the triangle-lattice plane and no long-range magnetic order down to 80 mK, as the quantum spin liquid candidate with dominant Ising-type interactions.

Local diversity of drought resistance and resilience in Populus tomentosa correlates with the variation of DNA methylation.

Little information is known about DNA methylation variation in shaping environment-specific drought resistance and resilience for tree adaptation. In this study, we leveraged RNA sequencing and whole-genome bisulfite sequencing data to dissect the distinction of epigenetic regulation under drought stress and rewater condition of Populus tomentosa accessions from three geographical regions. We demonstrated low resistance and high resilience for accessions from South. Non-CG methylation levels in promoter regions of Southern accessions were lower than accessions from higher latitudes and negatively regulated gene expression. CHH context methylation was more sensitive to drought stress, and the geographical-specific differentially methylated regions were scarcely changed by environmental fluctuation. We identified 60 conserved hub genes within the co-expression networks that correlate with photosynthetic and stomatal morphological traits. Epigenome-wide association studies and genome-wide association studies of these 60 hub genes revealed the interdependency between genetic and epigenetic variation in GATA9 and LECRK-VIII.2, which was associated with stomatal morphology and chlorophyll content. The natural epigenetic variation in GATA9 was also faithfully transmitted to progenies in two family-based F1 populations. This study indicates a functional relationship of DNA methylation diversity with drought resistance and resilience which offers new insights into plants' local adaptation to a stressful environment.

Leaf physiology variations are modulated by natural variations that underlie stomatal morphology in Populus.

Stomata are essential for photosynthesis and abiotic stress tolerance. Here, we used multiomics approaches to dissect the genetic architecture and adaptive mechanisms that underlie stomatal morphology in Populus tomentosa juvenile natural population (303 accessions). We detected 46 candidate genes and 15 epistatic gene-pairs, associated with 5 stomatal morphologies and 18 leaf development and photosynthesis traits, through genome-wide association studies. Expression quantitative trait locus mapping revealed that stomata-associated gene loci were significantly associated with the expression of leaf-related genes; selective sweep analysis uncovered significant differentiation in the allele frequencies of genes that underlie stomatal variations. An allelic regulatory network operating under drought stress and adequate precipitation conditions, with three key regulators (DUF538, TRA2 and AbFH2) and eight interacting genes, was identified that might regulate leaf physiology via modulation of stomatal shape and density. Validation of candidate gene variations in drought-tolerant and F1 hybrid populations of P. tomentosa showed that the DUF538, TRA2 and AbFH2 loci cause functional stabilisation of spatiotemporal regulatory, whose favourable alleles can be faithfully transmitted to offspring. This study provides insights concerning leaf physiology and stress tolerance via the regulation of stomatal determination in perennial plants.

Ba9RE2(SiO4)6 (RE = Ho-Yb): A Family of Rare-Earth-Based Honeycomb-Lattice Magnets.

Rare-earth (RE)-based honeycomb-lattice materials with strong spin-orbit coupled Jeff = 1/2 moments have attracted great interest as a platform to realize the Kitaev quantum spin liquid (QSL) state. Herein, we report the discovery of a family of RE-based honeycomb-lattice magnets Ba9RE2(SiO4)6 (RE = Ho-Yb), which crystallize into the rhombohedral structure with the space group R3̅. In these serial compounds, magnetic RE3+ ions are arranged on a perfect honeycomb lattice within the ab-plane and stacked in the "ABCABC"-type fashion along the c-axis. All synthesized Ba9RE2(SiO4)6 (RE = Ho-Yb) polycrystals exhibit the dominant antiferromagnetic interaction and absence of magnetic order down to 2 K. In combination with the magnetization and electron spin resonance results, magnetic behaviors are discussed for the compounds with different RE ions. Moreover, the as-grown Ba9Yb2(SiO4)6 single crystals show large magnetic frustration with frustration index f = θCW/TN > 8 and no long-range magnetic ordering down to 0.15 K, being a possible QSL candidate material. These series of compounds are attractive for exploring the exotic magnetic phases of Kitaev materials with 4f electrons.

Transcriptome analysis and association mapping reveal the genetic regulatory network response to cadmium stress in Populus tomentosa.

Long non-coding RNAs (lncRNAs) play essential roles in plant abiotic stress responses, but the response of lncRNA-mediated genetic networks to cadmium (Cd) treatment remain elusive in trees, the promising candidates for phytoremediation of Cd contamination. We identified 172 Cd-responsive lncRNAs and 295 differentially expressed target genes in the leaves of Cd-treated Populus tomentosa. Functional annotation revealed that these lncRNAs were involved in various processes, including photosynthesis, hormone regulation, and phenylalanine metabolism. Association studies identified 78 significant associations, representing 14 Cd-responsive lncRNAs and 28 target genes for photosynthetic and leaf physiological traits. Epistasis uncovered 83 pairwise interactions among these traits, revealing Cd-responsive lncRNA-mediated genetic networks for photosynthesis and leaf physiology in P. tomentosa. We focused on the roles of two Cd-responsive lncRNA-gene pairs, MSTRG.22608.1-PtoMYB73 and MSTRG.5634.1-PtoMYB27, in Cd tolerance of Populus, and detected insertions/deletions within lncRNAs as polymorphisms driving target gene expression. Genotype analysis of lncRNAs and heterologous overexpression of PtoMYB73 and PtoMYB27 in Arabidopsis indicated their effects on enhancing Cd tolerance, photosynthetic rate, and leaf growth, and the potential interaction mechanisms of PtoMYB73 with abiotic stresses. Our study identifies the genetic basis for the response of Populus to Cd treatment, facilitating genetic improvement of Cd tolerance in trees.

Genetic Architecture Underlying the Metabolites of Chlorogenic Acid Biosynthesis in Populus tomentosa.

Chlorogenic acid (CGA) plays a crucial role in defense response, immune regulation, and the response to abiotic stress in plants. However, the genetic regulatory network of CGA biosynthesis pathways in perennial plants remains unclear. Here, we investigated the genetic architecture for CGA biosynthesis using a metabolite-based genome-wide association study (mGWAS) and expression quantitative trait nucleotide (eQTN) mapping in a population of 300 accessions of Populus tomentosa. In total, we investigated 204 SNPs which were significantly associated with 11 metabolic traits, corresponding to 206 genes, and were mainly involved in metabolism and cell growth processes of P. tomentosa. We identified 874 eQTNs representing 1066 genes, in which the expression and interaction of causal genes affected phenotypic variation. Of these, 102 genes showed significant signatures of selection in three geographical populations, which provided insights into the adaptation of CGA biosynthesis to the local environment. Finally, we constructed a genetic network of six causal genes that coordinately regulate CGA biosynthesis, revealing the multiple regulatory patterns affecting CGA accumulation in P. tomentosa. Our study provides a multiomics strategy for understanding the genetic basis underlying the natural variation in the CGA biosynthetic metabolites of Populus, which will enhance the genetic development of abiotic-resistance varieties in forest trees.

Genetic Architecture and Genome-Wide Adaptive Signatures Underlying Stem Lenticel Traits in Populus tomentosa.

The stem lenticel is a highly specialized tissue of woody plants that has evolved to balance stem water retention and gas exchange as an adaptation to local environments. In this study, we applied genome-wide association studies and selective sweeping analysis to characterize the genetic architecture and genome-wide adaptive signatures underlying stem lenticel traits among 303 unrelated accessions of P. tomentosa, which has significant phenotypic and genetic variations according to climate region across its natural distribution. In total, we detected 108 significant single-nucleotide polymorphisms, annotated to 88 candidate genes for lenticel, of which 9 causative genes showed significantly different selection signatures among climate regions. Furthermore, PtoNAC083 and PtoMYB46 showed significant association signals and abiotic stress response, so we overexpressed these two genes in Arabidopsis thaliana and found that the number of stem cells in all three overexpression lines was significantly reduced by PtoNAC083 overexpression but slightly increased by PtoMYB46 overexpression, suggesting that both genes are involved in cell division and expansion during lenticel formation. The findings of this study demonstrate the successful application of an integrated strategy for dissecting the genetic basis and landscape genetics of complex adaptive traits, which will facilitate the molecular design of tree ideotypes that may adapt to future climate and environmental changes.

Mechanistically Driven Control over Cubane Oxo Cluster Catalysts.

Predictive and mechanistically driven access to polynuclear oxo clusters and related materials remains a grand challenge of inorganic chemistry. We here introduce a novel strategy for synthetic control over highly sought-after transition metal {M4O4} cubanes. They attract interest as molecular water oxidation catalysts that combine features of both heterogeneous oxide catalysts and nature's cuboidal {CaMn4O5} center of photosystem II. For the first time, we demonstrate the outstanding structure-directing effect of straightforward inorganic counteranions in solution on the self-assembly of oxo clusters. We introduce a selective counteranion toolbox for the controlled assembly of di(2-pyridyl) ketone (dpk) with M(OAc)2 (M = Co, Ni) precursors into different cubane types. Perchlorate anions provide selective access to type 2 cubanes with the characteristic {H2O-M2(OR)2-OH2} edge-site, such as [Co4(dpy-C{OH}O)4(OAc)2(H2O)2](ClO4)2. Type 1 cubanes with separated polar faces [Co4(dpy-C{OH}O)4(L2)4] n+ (L2 = OAc, Cl, or OAc and H2O) can be tuned with a wide range of other counteranions. The combination of these counteranion sets with Ni(OAc)2 as precursor selectively produces type 2 Co/Ni-mixed or {Ni4O4} cubanes. Systematic mechanistic experiments in combination with computational studies provide strong evidence for type 2 cubane formation through reaction of the key dimeric building block [M2(dpy-C{OH}O)2(H2O)4]2+ with monomers, such as [Co(dpy-C{OH}O)(OAc)(H2O)3]. Furthermore, both experiments and DFT calculations support an energetically favorable type 1 cubane formation pathway via direct head-to-head combination of two [Co2(dpy-C{OH}O)2(OAc)2(H2O)2] dimers. Finally, the visible-light-driven water oxidation activity of type 1 and 2 cubanes with tuned ligand environments was assessed. We pave the way to efficient design concepts in coordination chemistry through ionic control over cluster assembly pathways. Our comprehensive strategy demonstrates how retrosynthetic analyses can be implemented with readily available assembly directing counteranions to provide rapid access to tuned molecular materials.

{Co4O4} and {CoxNi4-xO4} Cubane Water Oxidation Catalysts as Surface Cut-Outs of Cobalt Oxides.

The future of artificial photosynthesis depends on economic and robust water oxidation catalysts (WOCs). Cobalt-based WOCs are especially promising for knowledge transfer between homogeneous and heterogeneous catalyst design. We introduce the active and stable {CoII4O4} cubane [CoII4(dpy{OH}O)4(OAc)2(H2O)2](ClO4)2 (Co4O4-dpk) as the first molecular WOC with the characteristic {H2O-Co2(OR)2-OH2} edge-site motif representing the sine qua non moiety of the most efficient heterogeneous Co-oxide WOCs. DFT-MD modelings as well as in situ EXAFS measurements indicate the stability of the cubane cage in solution. The stability of Co4O4-dpk under photocatalytic conditions ([Ru(bpy)3]2+/S2O82-) was underscored with a wide range of further analytical methods and recycling tests. FT-IR monitoring and HR-ESI-MS spectra point to a stable coordination of the acetate ligands, and DFT-MD simulations along with 1H/2H exchange experiments highlight a favorable intramolecular base functionality of the dpy{OH}O ligands. All three ligand types enhance proton mobility at the edge site through a unique bioinspired environment with multiple hydrogen-bonding interactions. In situ XANES experiments under photocatalytic conditions show that the {CoII4O4} core undergoes oxidation to Co(III) or higher valent states, which recover rather slowly to Co(II). Complementary ex situ chemical oxidation experiments with [Ru(bpy)3]3+ furthermore indicate that the oxidation of all Co(II) centers of Co4O4-dpk to Co(III) is not a mandatory prerequisite for oxygen evolution. Moreover, we present the [CoIIxNi4-x(dpy{OH}O)4(OAc)2(H2O)2](ClO4)2 (CoxNi4-xO4-dpk) series as the first mixed Co/Ni-cubane WOCs. They newly bridge homogeneous and heterogeneous catalyst design through fine-tuned edge-site environments of the Co centers.

Interlayer sp3 Bonds and Chirality at Bilayer Graphene Oxide/Calcium Silicate Hydrate Abnormally Enhance Its Interlayer Stress Transfer.

Graphene oxide (GO) is an ideal reinforcing material with super design capability, which can achieve the combination of strength and toughness. However, the actual effect of GO is far below the theoretical prediction. This is mainly due to the weak interface between the nanofiller and the matrix. In this paper, a controllable method for improving interlayer stress transfer of double-layer graphene oxide/C-S-H (D-GO-CSH)-layered nanostructures is proposed by using interlayer sp3 bond and chirality. The results show that, compared with the control group, the normalized shear stress and normalized pull-out energy of the OH-sp3 model are increased by 44.93 and 49.25%, respectively, while those of the OO-sp3 model are increased by 32.26 and 31.03%, respectively. The interlayer sp3 bonds lead to a great enhancement (more than 3 times) in normalized interlayer stress transfer of D-GO-CSH-layered nanostructures while exerting a little opposite effect (about 5%). The improvement effects induced by the interlayer sp3 bonds are also strongly dependent on their distributions and the chirality of GO. According to the fracture mechanic theory and molecular dynamics results, the strain energy percentage difference (bond length and bond angle) of the zigzag-cen model is 34.8% lower than that of the control group model, which proves that the interlayer sp3 bonds have a remarkably positive effect on the interlayer stress transfer of D-GO-CSH-layered nanostructures. This provides a new way to further improve the interlayer stress transfer, pull-out energy, and interlayer shear stress of D-GO-CSH-layered nanostructures.

Mechanistic Insights into How the Single Point Mutation Change the Autoantibody Repertoire.

A recent study showed that just one point mutation F33 to Y in the complementarity-determining region 1 of heavy chain (H-CDR1) could lead to the auto-antibody losing its DNA binding ability. However, the potential molecular mechanisms have not been well elucidated. In this study, we investigated how the antibody lost the DNA binding ability caused by mutation F33 to Y in the H-CDR1. We found that the electrostatic force was not the primary driving force for the interaction between anti-DNA antibodies and the antigen single strand DNA (ssDNA), and that the H-CDR2 largely contributed to the binding of antigen ssDNA, even larger than H-CDR1. The H-F33Y mutation could increase the hydrogen-bond interaction but impair the pi-pi stacking interaction between the antibody and ssDNA. We further found that F33H, W98H and Y95L in the wiletype antibody could form the stable pi-pi stacking interaction with the nucleotide bases of ssDNA. However, the Y33 in mutant could not form the parallel sandwich pi-pi stacking interaction with the ssDNA. To further confirm the importance of pi-pi stacking, the wildtype antibody and the mutants (F33YH, F33AH, W98AH and Y95AL) were experimentally expressed in CHO cells and purified, and the results from ELISA clearly showed that all the mutants lost the ssDNA binding ability. Taken together, our findings may not only deepen the understanding of the underlying interaction mechanism between autoantibody and antigen, but also broad implications in the field of antibody engineer.

Preparation and Characterization of Phenolic Acid-Chitosan Derivatives as an Edible Coating for Enhanced Preservation of Saimaiti Apricots.

In this study, caffeic acid (CA) and chlorogenic acid (CGA) were incorporated onto chitosan (CS) using free radical grafting initiated by a hydrogen peroxide/ascorbic acid (H2O2/Vc) redox system. The structural properties of the CA (CA-g-CS) and CGA (CGA-g-CS) derivatives were characterized by UV-Vis absorption, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and thermal stability analysis. Then, the antioxidant and antibacterial properties were evaluated, and the effect of CGA-g-CS on the postharvest quality of Saimaiti apricot was studied. It proved that phenolic acids were successfully grafted onto the CS. The grafting ratios of CA-g-CS and CGA-g-CS were 126.21 mg CAE/g and 148.94 mg CGAE/g. The antioxidation and antibacterial activities of CGA-g-CS were better than those of CA-g-CS. The MICs of CGA-g-CS against E. coli, S. aureus, and B. subtilis were 2, 1, and 2 mg/mL. The inhibitory zones of 20 mg/mL CGA-g-CS against the three bacteria were 19.16 ± 0.35, 16.33 ± 0.91, and 16.24 ± 0.05 mm. The inhibitory effects of 0.5% CGA-g-CS on the firmness, weight loss, SSC, TA, relative conductivity, and respiration rate of the apricot were superior. Our results suggest that CGA-g-CS can be potentially used as an edible coating material to preserve apricots.

Transcriptome and association mapping revealed functional genes respond to drought stress in Populus.

Drought frequency and severity are exacerbated by global climate change, which could compromise forest ecosystems. However, there have been minimal efforts to systematically investigate the genetic basis of the response to drought stress in perennial trees. Here, we implemented a systems genetics approach that combines co-expression analysis, association genetics, and expression quantitative trait nucleotide (eQTN) mapping to construct an allelic genetic regulatory network comprising four key regulators (PtoeIF-2B, PtoABF3, PtoPSB33, and PtoLHCA4) under drought stress conditions. Furthermore, Hap_01PtoeIF-2B, a superior haplotype associated with the net photosynthesis, was revealed through allelic frequency and haplotype analysis. In total, 75 candidate genes related to drought stress were identified through transcriptome analyses of five Populus cultivars (P. tremula × P. alba, P. nigra, P. simonii, P. trichocarpa, and P. tomentosa). Through association mapping, we detected 92 unique SNPs from 38 genes and 104 epistatic gene pairs that were associated with six drought-related traits by association mapping. eQTN mapping unravels drought stress-related gene loci that were significantly associated with the expression levels of candidate genes for drought stress. In summary, we have developed an integrated strategy for dissecting a complex genetic network, which facilitates an integrated population genomics approach that can assess the effects of environmental threats.

Effect of Corroded Surface Morphology on Ultra-Low Cycle Fatigue of Steel Bridge Piers.

Corrosion is a common form of durability degradation of steel bridges. Corrosion morphology affects stress distribution under cyclic loads and causes strain concentrations in pits, thus affecting the mechanical properties of steel structures, including ultra-low cycle fatigue (ULCF). To precisely simulate corrosion morphology and investigate the ULCF failure mechanism of corroded steel piers, a sculpting method was applied to mesh units using three-dimensional surface morphology data of corroded steel specimens. Moreover, the ULCF crack-initiation life was numerically predicted using the finite element model based on the cyclic void growth model (CVGM). The cumulative equivalent plastic strain, cyclic void growth index, and critical void growth index of corroded steel piers with different corroded morphologies were compared. Results reveal that, regardless of whether the pier is corroded, fatigue cracks tend to initiate at the weld toe at corners when exposed to cyclic loads under an oblique direction at the pier top. Additionally, the ULCF crack-initiation life in a corroded pier is less than that in an uncorroded pier, and it is significantly affected by a reduction in the pier wall thickness. Corrosion pits affect the position of ULCF crack initiation in a steel pier and cracks tend to initiate at the bottom of pits with large depth-to-diameter ratios. In the case of minor corrosion, the corrosion morphology affects the seismic performance of piers to a small extent.

OsIAA20, an Aux/IAA protein, mediates abiotic stress tolerance in rice through an ABA pathway.

In plants, auxin and ABA play significant roles in conferring tolerance to environmental abiotic stresses. Earlier studies have been shown that some Aux/IAA genes, with important signaling factors in the auxin pathway, were induced in response to drought and other abiotic stresses. However, the mechanistic links between Aux/IAA expression and general drought response remain largely unknown. In this study, OsIAA20, a rice Aux/IAA protein, shown with important roles in abiotic stress. Phenotypic analyses revealed that OsIAA20 RNAi transgenic rice reduced drought and salt tolerance; whereas, OsIAA20 overexpression plants displayed the opposite phenotype. Physiological analyses of OsIAA20 RNAi rice grown under drought or salt stress showed that proline and chlorophyll content significantly decreased, while malondialdehyde content and the ratio of Na+/ K+ significantly increased. In addition, OsIAA20down-regulation reduced stomatal closure and increased the rate of water loss, while transgenic plants overexpressing OsIAA20 exhibited the opposite physiological responses. Furthermore, an ABA-responsive gene, OsRab21, was down-regulated in OsIAA20 RNAi rice lines and upregulated in OsIAA20 overexpression plants. Those results means OsIAA20 played an important role in plant drought and salt stress responses, by an ABA dependent mechanism, and it will be a candidate target gene used to breed abiotic stress tolerance.

Transcription factors involved in the regulatory networks governing the Calvin-Benson-Bassham cycle.

Transcription factors (TFs) play crucial roles in the regulation of photosynthesis; elucidating these roles will facilitate our understanding of photosynthesis and thus accelerate its improvement for enhancing crop yield. Promoter analysis of 52 nuclear-encoded Populus tomentosa Carr. genes involved in the Calvin-Benson-Bassham (CBB) cycle revealed 706 motifs and 326 potentially interacting TFs. A backward elimination random forest (BWERF) algorithm reduced the number of TFs to 40, involved in a three-layer gene regulatory network (GRN) including 46 photosynthesis genes (bottom layer), 25 TFs (second layer) and 15 TFs (top layer). Phenotype-genotype association identified 248 single-nucleotide polymorphisms (SNPs) within 72 genes associated with 11 photosynthesis traits. Of the regulatory pairs identified by the BWERF (202 pairs), 77 TF-target combinations harbored SNPs associated with the same trait, supporting similar mechanisms of phenotype modulation. We used expression quantitative trait nucleotide (eQTN) analysis to identify causal SNPs affecting gene expression, identifying 1851 eQTN signals for 50 eGenes (genes whose expressions are regulated by eQTNs). Distribution patterns identified 14 eQTNs from seven TFs associated with eight expression levels of their downstream targets (defined in the GRN), whereas seven TF-target pairs were also identified by phenotype-genotype associations. To further validate the roles of TFs at the metabolic level, we selected 6764 SNPs from 55 genes (identified by GRN-association or GRN-eQTN pairs or both) for metabolic association, identifying variants within 10 TFs affecting metabolic processes underlying the CBB cycle. Our study provides new insights into the photosynthesis pathway in poplar and may facilitate understanding of processes underlying photosynthesis improvement.

Photoinduced Oxygen Evolution Catalysis Promoted by Polyoxometalate Salts of Cationic Photosensitizers.

The insoluble salt Cs15K[Co9(H2O)6(OH)3(HPO4)2(PW9O34)3] (CsCo9) is tested as heterogeneous oxygen evolution catalyst in light-induced experiments, when combined with the homogeneous photosensitizer [Ru(bpy)3]2+ and the oxidant Na2S2O8 in neutral pH. Oxygen evolution occurs in parallel to a solid transformation. Post-catalytic essays indicate that the CsCo9 salt is transformed into the corresponding [Ru(bpy)3]2+ salt, upon cesium loss. Remarkably, analogous photoactivated oxygen evolution experiments starting with the [Ru(bpy)3](5+x)K(6-2x)[Co9(H2O)6(OH)3(HPO4)2(PW9O34)3]·(39+x)H2O (RuCo9) salt demonstrate much higher efficiency and kinetics. The origin of this improved performance is at the cation-anion, photosensitizer-catalyst pairing in the solid state. This is beneficial for the electron transfer event, and for the long-term stability of the photosensitizer. The latter was confirmed as the limiting process during these oxygen evolution reactions, with the polyoxometalate catalyst exhibiting robust performance in multiple cycles, upon addition of photosensitizer, and/or oxidant to the reaction mixture.

Association Genetics in Populus Reveal the Allelic Interactions of Pto-MIR167a and Its Targets in Wood Formation.

MicroRNAs (miRNAs) play crucial regulatory roles in plant growth and development by interacting with RNA molecules, including messenger RNAs (mRNAs) and long non-coding RNAs (lncRNAs); however, the genetic networks of miRNAs and their targets influencing the phenotypes of perennial trees remain to be investigated. Here, we integrated expression profiling and association analysis of underlying physiology and expression traits to dissect the allelic variations and genetic interactions of Pto-MIR167a and its targets, sponge lncRNA ARFRL, and Pto-ARF8, in 435 unrelated individuals of Populus tomentosa. Tissue-specific expression analysis in eight tissues, including stem, leaf, root, and shoot apex, revealed negative correlations between Pto-MIR167a and lncRNA ARFRL and Pto-ARF8 (r = -0.60 and -0.61, respectively, P < 0.01), and a positive correlation between sponge lncRNA ARFRL and Pto-ARF8 (r = 0.90, P < 0.01), indicating their potential regulatory roles in tree growth and wood formation. Single nucleotide polymorphism (SNP)-based association studies detected 53 significant associations (P < 0.01, Q < 0.1) representing 41 unique SNPs from the three genes and six traits, suggesting their potential roles in wood formation. Epistasis uncovered 88 pairwise interactions for 10 traits, which provided substantial evidence for genetic interactions among Pto-MIR167a, lncRNA ARFRL, and Pto-ARF8. Using gene expression-based association mapping, we also examined SNPs within the three genes that influence phenotypes by regulating the expression of Pto-ARF8. Interestingly, SNPs in the precursor region of Pto-MIR167a altered its secondary structure stability and transcription, thereby affecting the expression of its targets. In summary, we elucidated the genetic interactions between Pto-MIR167a and its targets, sponge lncRNA ARFRL, and Pto-ARF8, in tree growth and wood formation, and provide a feasible method for further investigation of multi-factor genetic networks influencing phenotypic variation in the population genetics of trees.

Genome-Wide Association Studies to Improve Wood Properties: Challenges and Prospects.

Wood formation is an excellent model system for quantitative trait analysis due to the strong associations between the transcriptional and metabolic traits that contribute to this complex process. Investigating the genetic architecture and regulatory mechanisms underlying wood formation will enhance our understanding of the quantitative genetics and genomics of complex phenotypic variation. Genome-wide association studies (GWASs) represent an ideal statistical strategy for dissecting the genetic basis of complex quantitative traits. However, elucidating the molecular mechanisms underlying many favorable loci that contribute to wood formation and optimizing GWAS design remain challenging in this omics era. In this review, we summarize the recent progress in GWAS-based functional genomics of wood property traits in major timber species such as Eucalyptus, Populus, and various coniferous species. We discuss several appropriate experimental designs for extensive GWAS in a given undomesticated tree population, such as omics-wide association studies and high-throughput phenotyping technologies. We also explain why more attention should be paid to rare allelic and major structural variation. Finally, we explore the potential use of GWAS for the molecular breeding of trees. Such studies will help provide an integrated understanding of complex quantitative traits and should enable the molecular design of new cultivars.