Gapless biosynthetic pathway enables sustainable paclitaxel production.

A recent leading-edge study by Jiang et al. identified two enzymes that are responsible for key reactions in the biosynthesis of baccatin III. The authors successfully reconstructed the baccatin III synthesis pathway with a minimal number of synthetic enzymes in tobacco leaves, laying the foundation for industrial-scale sustainable production of the anticancer drug paclitaxel.

Strigolactones shape the assembly of root-associated microbiota in response to phosphorus availability.

Plants rely on strigolactones (SLs) to regulate their development and form symbiotic relationships with microbes as part of the adaptive phosphorus (P) efficiency strategies. However, the impact of SLs on root-associated microbial communities in response to P availability remains unknown. Here, root microbiota of SL biosynthesis (max3-11) and perception (d14-1) were compared to wild-type Col-0 plants under different P concentrations. Using high-throughput sequencing, the relationship between SLs, P concentrations, and the root-associated microbiota was investigated to reveal the variation in microbial diversity, composition, and interaction. Plant genotypes and P availability played important but different roles in shaping the root-associated microbial community. Importantly, SLs were found to attract Acinetobacter in low P conditions, which included an isolated CP-2 (Acinetobacter soli) that could promote plant growth in cocultivation experiments. Moreover, SLs could change the topologic structure within co-occurrence networks and increase the number of keystone taxa (e.g., Rhizobiaceae and Acidobacteriaceae) to enhance microbial community stability. This study reveals the key role of SLs in mediating root-associated microbiota interactions.IMPORTANCEStrigolactones (SLs) play a crucial role in plant development and their symbiotic relationships with microbes, particularly in adapting to phosphorus levels. Using high-throughput sequencing, we compared the root microbiota of plants with SL biosynthesis and perception mutants to wild-type plants under different phosphorus concentrations. These results found that SLs can attract beneficial microbes in low phosphorus conditions to enhance plant growth. Additionally, SLs affect microbial network structures, increasing the stability of microbial communities. This study highlights the key role of SLs in shaping root-associated microbial interactions, especially in response to phosphorus availability.

SMXL5 attenuates strigolactone signaling in Arabidopsis thaliana by inhibiting SMXL7 degradation.

Hormone-activated proteolysis is a recurring theme of plant hormone signaling mechanisms. In strigolactone signaling, the enzyme receptor DWARF14 (D14) and an F-box protein, MORE AXILLARY GROWTH2 (MAX2), mark SUPPRESSOR OF MAX2 1-LIKE (SMXL) family proteins SMXL6, SMXL7, and SMXL8 for rapid degradation. Removal of these transcriptional corepressors initiates downstream growth responses. The homologous proteins SMXL3, SMXL4, and SMXL5, however, are resistant to MAX2-mediated degradation. We discovered that the smxl4 smxl5 mutant has enhanced responses to strigolactone. SMXL5 attenuates strigolactone signaling by interfering with AtD14-SMXL7 interactions. SMXL5 interacts with AtD14 and SMXL7, providing two possible ways to inhibit SMXL7 degradation. SMXL5 function is partially dependent on an ethylene-responsive-element binding-factor-associated amphiphilic repression (EAR) motif, which typically mediates interactions with the TOPLESS family of transcriptional corepressors. However, we found that loss of the EAR motif reduces SMXL5-SMXL7 interactions and the attenuation of strigolactone signaling by SMXL5. We hypothesize that integration of SMXL5 into heteromeric SMXL complexes reduces the susceptibility of SMXL6/7/8 proteins to strigolactone-activated degradation and that the EAR motif promotes the formation or stability of these complexes. This mechanism may provide a way to spatially or temporally fine-tune strigolactone signaling through the regulation of SMXL5 expression or translation.

Dual-Effect Coupling for Superior Dielectric and Thermal Conductivity of Polyimide Composite Films Featuring "Crystal-Like Phase" Structure.

To match the increasing miniaturization and integration of electronic devices, higher requirements are put on the dielectric and thermal properties of the dielectrics to overcome the problems of delayed signal transmission and heat accumulation. Here, a 3D  porous thermal conductivity network is successfully constructed inside the polyimide (PI) matrix by the combination of ionic liquids (IL) and calcium fluoride (CaF2 ) nanofillers, motivated by the bubble-hole forming orientation force. Benefiting from the 3D thermal network formed by IL as a porogenic template and "crystal-like phase" structures induced by CaF2 - polyamide acid charge transfer, IL-10 vol% CaF2 /PI porous film exhibits a low permittivity of 2.14 and a thermal conductivity of 7.22 W m-1 K-1 . This design strategy breaks the bottleneck that low permittivity and high thermal conductivity in microelectronic systems are difficult to be jointly controlled, and provides a feasible solution for the development of intelligent microelectronics.

On-Particle Hyperbranched Rolling Circle Amplification-Scaffolded Magnetic Nanoactuator Assembly for Ferromagnetic Resonance Detection of MicroRNA.

Inspired by natural molecular machines, scientists are devoted to designing nanomachines that can navigate in aqueous solutions, sense their microenvironment, actuate, and respond. Among different strategies, magnetically driven nanoactuators can easily be operated remotely in liquids and thus are valuable in biosensing. Here we report a magnetic nanoactuator swarm with rotating-magnetic-field-controlled conformational changes for reaction acceleration and target quantification. By grafting nucleic acid amplification primers, magnetic nanoparticle (MNP) actuators can assemble and be fixed with a flexible DNA scaffold generated by surface-localized hyperbranched rolling circle amplification in response to the presence of a target microRNA, osa-miR156. Net magnetic anisotropy changes of the system induced by the MNP assembly can be measured by ferromagnetic resonance spectroscopy as shifts in the resonance field. With a total assay time of ca. 120 min, the proposed biosensor offers a limit of detection of 6 fM with a dynamic detection range spanning 5 orders of magnitude. The specificity of the system is validated by testing different microRNAs and salmon sperm DNA. Endogenous microRNAs extracted from Oryza sativa leaves are tested with both quantitative reverse transcription-PCR and our approach, showing comparable performances with a Pearson correlation coefficient >0.9 (n = 20).

Mechanism of sphingolipid homeostasis revealed by structural analysis of Arabidopsis SPT-ORM1 complex.

The serine palmitoyltransferase (SPT) complex catalyzes the first and rate-limiting step in sphingolipid biosynthesis in all eukaryotes. ORM/ORMDL proteins are negative regulators of SPT that respond to cellular sphingolipid levels. However, the molecular basis underlying ORM/ORMDL-dependent homeostatic regulation of SPT is not well understood. We determined the cryo-electron microscopy structure of Arabidopsis SPT-ORM1 complex, composed of LCB1, LCB2a, SPTssa, and ORM1, in an inhibited state. A ceramide molecule is sandwiched between ORM1 and LCB2a in the cytosolic membrane leaflet. Ceramide binding is critical for the ORM1-dependent SPT repression, and dihydroceramides and phytoceramides differentially affect this repression. A hybrid ß sheet, formed by the amino termini of ORM1 and LCB2a and induced by ceramide binding, stabilizes the amino terminus of ORM1 in an inhibitory conformation. Our findings provide mechanistic insights into sphingolipid homeostatic regulation via the binding of ceramide to the SPT-ORM/ORMDL complex that may have implications for plant-specific processes such as the hypersensitive response for microbial pathogen resistance.

Magnetic DNA Nanomachine for On-Particle Cascade Amplification-Based Ferromagnetic Resonance Detection of Plant MicroRNA.

Plant microRNAs play critical roles in post-transcriptional gene regulation of many processes, thus motivating the development of accurate and user-friendly microRNA detection methods for better understanding of, e.g., plant growth, development, and abiotic/biotic stress responses. By integrating the capture probe, fuel strand, primer, and template onto the surface of a magnetic nanoparticle (MNP), we demonstrated a magnetic DNA nanomachine that could conduct an on-particle cascade amplification reaction in response to the presence of target microRNA. The cascade amplification consists of an exonuclease III-assisted target recycling step and a rolling circle amplification step, leading to changes in the MNP arrangement that can be quantified by ferromagnetic resonance spectroscopy. After a careful investigation of the exonuclease III side reaction, the biosensor offers a detection limit of 15 fM with a total assay time of ca. 70 min. Moreover, our magnetic DNA nanomachine is capable of discriminating the target microRNA from its family members. Our biosensor has also been tested on total endogenous microRNAs extracted from Arabidopsis thaliana leaves, with a performance comparable to qRT-PCR.

Hypoxia and TNF-α Synergistically Induce Expression of IL-6 and IL-8 in Human Fibroblast-like Synoviocytes via Enhancing TAK1/NF-κB/HIF-1α Signaling.

Hypoxia and increased levels of inflammatory cytokines in the joints are characteristics of rheumatoid arthritis (RA). However, the effects of hypoxia and tumor necrosis factor-α (TNF-α) on interleukin (IL)-6 and IL-8 production on fibroblast-like synoviocytes (FLSs) remain to be clarified. This study aimed to explore how hypoxia and TNF-α affect the expression of IL-6 and IL-8 in human FLSs isolated from RA patients. Hypoxia or TNF-α treatment alone significantly increased the expression and promoter activity of IL-6, IL-8, and hypoxia-inducible factor-1α (HIF-1α). Treatment of hypoxic FLSs with TNF-α further significantly elevated the expression of these cytokines and enhanced promoter activity of HIF-1α, which was abrogated by treatment with the HIF-1α inhibitor YC-1. Similarly, TNF-α alone elevated the phosphorylation and promoter activity of nuclear factor-κBp65 (NF-κBp65) in the FLSs. These effects were further enhanced by the combined treatment of hypoxia and TNFα but were attenuated by the NF-κB inhibitor BAY11-7082. NF-κB-p65 inhibition decreased the effect of TNF-α on HIF-1α upregulation in the FLSs in response to hypoxia. The combination of hypoxia and TNF-α also significantly upregulated transforming growth factor-ß-activated kinase 1 (TAK1) expression, and silencing TAK1 dramatically decreased NF-κB-p65, HIF-1α, IL-6, and IL-8 expression under the same conditions. Our results indicate that hypoxia and TNF-α synergistically increase IL-6 and IL-8 expression in human FLSs via enhancing TAK1/NF-κB/HIF-1α signaling.

TcJAV3-TcWRKY26 Cascade Is a Missing Link in the Jasmonate-Activated Expression of Taxol Biosynthesis Gene DBAT in Taxus chinensis.

Jasmonates (JAs) are the most effective inducers for the biosynthesis of various secondary metabolites. Currently, jasmonate ZIM domain (JAZ) and its interactors, such as MYC2, constitute the main JA signal transduction cascade, and such a cascade fails to directly regulate all the taxol biosynthesis genes, especially the rate-limit gene, DBAT. Another JA signaling branch, JAV and WRKY, would probably fill the gap. Here, TcJAV3 was the closest VQ-motif-containing protein in Taxus chinensis to AtJAV1. Although TcJAV3 was overexpressed in AtJAV1 knockdown mutant, JAVRi17, the enhanced disease resistance to Botrytis cinerea caused by silencing AtJAV1 was completely recovered. The results indicated that TcJAV3 indeed transduced JA signal as AtJAV1. Subsequently, TcWRKY26 was screened out to physically interact with TcJAV3 by using a yeast two-hybrid system. Furthermore, bimolecular fluorescence complementation and luciferase complementary imaging also confirmed that TcJAV3 and TcWRKY26 could form a protein complex in vivo. Our previous reports showed that transient TcWRKY26 overexpression could remarkably increase DBAT expression. Yeast one-hybrid and luciferase activity assays revealed that TcWRKY26 could directly bind with the wa-box of the DBAT promoter to activate downstream reporter genes. All of these results indicated that TcWRKY26 acts as a direct regulator of DBAT, and the TcJAV3−TcWRKY26 complex is actually another JA signal transduction mode that effectively regulates taxol biosynthesis in Taxus. Our results revealed that JAV−WRKY complexes directly regulated DBAT gene in response to JA stimuli, providing a novel model for JA-regulated secondary metabolism. Moreover, JAV could also transduce JA signal and function non-redundantly with JAZ during the regulation of secondary metabolisms.

Strigolactone signaling complex formation in yeast: A paradigm for studying hormone-induced receptor interaction with multiple downstream proteins.

Strigolactones (SLs) are bioactive carotenoid derivatives which function as signaling molecules to regulate plant architecture, nutrient absorption and communication with other organisms. The α/ß-fold hydrolase, D14, hydrolyzes SLs, and the hydrolysis product activates D14 to bind to downstream signaling partners, including an E3 ubiquitin ligase MAX2 and SMXL6/7/8 proteins. What was not known was whether binding with one downstream partner would alter the affinity of D14 for other binding partners. Here, we developed an efficient yeast four-hybrid (Y4H) detection system and demonstrate that SL induces the interaction of D14 with both SMXL7 and MAX2 in a dose-dependent manner. Moreover, using our newly established yeast four-hybrid system, we found that the SL-induced D14 interaction with SMXL7 was strengthened by MAX2 while SMXL7 weakened the SL-induced D14 interaction with MAX2. Our findings provide novel insights into the regulatory effects of these signaling components and shed light on the molecular mechanism controlling the core SL signaling pathway. Furthermore, the heterologous yeast platform used for investigating SL complex formation has great potential to explore dynamic interactions in other signaling pathways or elucidate the unknown complex formation for biosynthesis of the parent carotenoids of SLs.

Probing strigolactone perception mechanisms with rationally designed small-molecule agonists stimulating germination of root parasitic weeds.

The development of potent strigolactone (SL) agonists as suicidal germination inducers could be a useful strategy for controlling root parasitic weeds, but uncertainty about the SL perception mechanism impedes real progress. Here we describe small-molecule agonists that efficiently stimulate Phelipanchce aegyptiaca, and Striga hermonthica, germination in concentrations as low as 10-8 to 10-17 M. We show that full efficiency of synthetic SL agonists in triggering signaling through the Striga SL receptor, ShHTL7, depends on the receptor-catalyzed hydrolytic reaction of the agonists. Additionally, we reveal that the stereochemistry of synthetic SL analogs affects the hydrolytic ability of ShHTL7 by influencing the probability of the privileged conformations of ShHTL7. Importantly, an alternative ShHTL7-mediated hydrolysis mechanism, proceeding via nucleophilic attack of the NE2 atom of H246 to the 2'C of the D-ring, is reported. Together, our findings provide insight into SL hydrolysis and structure-perception mechanisms, and potent suicide germination stimulants, which would contribute to the elimination of the noxious parasitic weeds.

Orchestrating plant direct and indirect phosphate uptake pathways.

A recent groundbreaking study by Shi et al. reveals an extensive transcriptional regulatory network for arbuscular mycorrhizal (AM) symbiosis in rice. The finding that phosphate starvation response (PHR) transcription factors centrally orchestrate the direct and indirect AM pathways for inorganic phosphate (Pi) uptake in rice opens a wealth of opportunities for plant breeding to enhance nutrient acquisition.

Identification of Conserved and Divergent Strigolactone Receptors in Sugarcane Reveals a Key Residue Crucial for Plant Branching Control.

Strigolactones (SLs) are a class of important plant hormones mainly regulating plant architecture such as branching, which is crucial for crop yield. It is valuable to study SL signaling pathway and its physiological function in sugarcane, the most important sugar crop, for further molecular breeding. Here, two putative SL receptors SsD14a/b and the interacting F-box protein SsMAX2 were identified in Saccharum spontaneum. SL induced both SsD14a and SsD14b to interact with SsMAX2 in yeast. SsD14a, but not SsD14b, could bind with AtMAX2 and AtSMXL7/SsSMXL7. Overexpression of SsD14a or SsMAX2 rescued the increased branching phenotypes of Arabidopsis thaliana d14-1 or max2-3 mutants, respectively. Moreover, the crystal structure of N-terminal truncated SsD14a was solved, with an overall structure identical to AtD14 and OsD14 in the open state, consistent with its conserved branching suppression capacity in Arabidopsis. In line with the biochemical observations, SsD14b could not completely complement in d14-1 although these two SsD14 proteins have almost identical primary sequences except for very few residues. Complement with the combination of SsD14b and SsMAX2 still failed to rescue the d14-1 max2-3 double mutant multi-branching phenotype, indicating SsD14b-AtSMXL7 complex formation is required for regulating branching. Mutagenesis analyses revealed that residue R310 at α10 helix of SsD14a was crucial for the binding with SsSMXL7/AtSMXL7 but not SsMAX2. The site-equivalent single-residue P304R substitution enabled SsD14b to bind with AtMAX2 and AtSMXL7/SsSMXL7 and to rescue the phenotype of d14-1 max2-3 together with SsMAX2. Moreover, this conserved Arg residue across species including rice and Arabidopsis determined the activity of SL receptors through maintaining their interaction with SMXL repressors. Taken together, our work identified conserved and divergent strigolactone receptors in sugarcane core SL signaling pathway and revealed a key residue crucial for plant branching control.

Lectin receptor-like kinase LecRK-VIII.2 is a missing link in MAPK signaling-mediated yield control.

The energy allocation for vegetative and reproductive growth is regulated by developmental signals and environmental cues, which subsequently affects seed output. However, the molecular mechanism underlying how plants coordinate yield-related traits to control yield in changing source-sink relationships remains largely unknown. Here, we discovered the lectin receptor-like kinase LecRK-VIII.2 as a specific receptor-like kinase that coordinates silique number, seed size, and seed number to determine seed yield in Arabidopsis (Arabidopsis thaliana). The lecrk-VIII.2 mutants develop smaller seeds, but more siliques and seeds, leading to increased yield. In contrast, the plants overexpressing LecRK-VIII.2 form bigger seeds, but less siliques and seeds, which results in similar yield to that of wild-type plants. Interestingly, LecRK-VIII.2 promotes the growth of the rosette, root, and stem by coordinating the source-sink relationship. Additionally, LecRK-VIII.2 positively regulates cell expansion and proliferation in the seed coat, and maternally controls seed size. The genetic and biochemical analyses demonstrated that LecRK-VIII.2 acts upstream of the mitogen-activated protein kinase (MAPK) gene MPK6 to regulate silique number, seed size, and seed number. Collectively, these findings uncover LecRK-VIII.2 as an upstream component of the MAPK signaling pathway to control yield-related traits and suggest its potential for crop improvement aimed at developing plants with stable yield, a robust root system, and improved lodging resistance.

Trirelaxor Ferroelectric Material with Giant Dielectric Permittivity over a Wide Temperature Range.

Advanced ferroelectrics with a combination of large dielectric response and good temperature stability are crucial for many technologically important electronic devices and electrical storage/power equipment. However, the two key factors usually do not go hand in hand, and achieving high permittivity is normally at the expense of sacrificing temperature stability. This trade-off relation is eased but not fundamentally remedied using relaxor-type materials which are known to have a diffuse permittivity peak at their relaxor transition temperatures. Here, we report an anomalous trirelaxor phenomenon in a barium titanate system and show that it can lead to a giant dielectric permittivity (εr ≈ 18 000) over a wide temperature range (Tspan ≈ 34K), which successfully overcomes a long-standing permittivity-stability trade-off. Moreover, the enhancement in the dielectric properties also yields a desired temperature-insensitive electrocaloric performance for the trirelaxor ferroelectrics. Microstructure characterization and phase-field simulations reveal a mixture of tetragonal, orthorhombic, and rhombohedral polar nanoregions over a broad temperature window in trirelaxor ferroelectrics, which is responsible for this combination of giant dielectric permittivity and good temperature stability. This finding provides an effective approach in designing advanced ferroelectrics with high performance and thermal stability.

Molecular basis for high ligand sensitivity and selectivity of strigolactone receptors in Striga.

Seeds of the root parasitic plant Striga hermonthica can sense very low concentrations of strigolactones (SLs) exuded from host roots. The S. hermonthica hyposensitive to light (ShHTL) proteins are putative SL receptors, among which ShHTL7 reportedly confers sensitivity to picomolar levels of SL when expressed in Arabidopsis thaliana. However, the molecular mechanism underlying ShHTL7 sensitivity is unknown. Here we determined the ShHTL7 crystal structure and quantified its interactions with various SLs and key interacting proteins. We established that ShHTL7 has an active-site pocket with broad-spectrum response to different SLs and moderate affinity. However, in contrast to other ShHTLs, we observed particularly high affinity of ShHTL7 for F-box protein AtMAX2. Furthermore, ShHTL7 interacted with AtMAX2 and with transcriptional regulator AtSMAX1 in response to nanomolar SL concentration. ShHTL7 mutagenesis analyses identified surface residues that contribute to its high-affinity binding to AtMAX2 and residues in the ligand binding pocket that confer broad-spectrum response to SLs with various structures. Crucially, yeast-three hybrid experiments showed that AtMAX2 confers responsiveness of the ShHTL7-AtSMAX1 interaction to picomolar levels of SL in line with the previously reported physiological sensitivity. These findings highlight the key role of SL-induced MAX2-ShHTL7-SMAX1 complex formation in determining the sensitivity to SL. Moreover, these data suggest a strategy to screen for compounds that could promote suicidal seed germination at physiologically relevant levels.

HbCOI1 perceives jasmonate to trigger signal transduction in Hevea brasiliensis.

Natural rubber, a strategically essential raw material used in manufacturing throughout the world, is produced from coagulated and refined latex of rubber tree (Hevea brasiliensis). It is known that phytohormone jasmonate (JA) plays an essential role in regulating latex biosynthesis. However, it is unclear how the JA signal is sensed in a rubber tree. Here, we showed that H. brasiliensis CORONATINE-INSENSITIVE 1 (HbCOI1) acts as a receptor that perceives JA to recruit H. brasiliensis JASMONATE ZIM DOMAIN1 (HbJAZ1) for signal transduction. We found that HbCOI1 restores male sterility and JA responses of the coi1-1 mutant in Arabidopsis. The identification of a JA receptor in the rubber tree is essential for elucidating the molecular mechanisms underlying JA-regulated latex biosynthesis. Our results elucidate the mechanism of JA perception in H. brasiliensis and also provide an efficient strategy to identify JA receptors in woody plants.

Dynamic Perception of Jasmonates by the F-Box Protein COI1.

Jasmonates (JAs) are cyclic fatty acid-derived phytohormones that regulate diverse aspects of plant defense and development. The endogenous active JA molecule (+)-7-iso-JA-L-Ile (JA-Ile) and its analog coronatine trigger formation of a complex with the F-box protein COI1 and JAZ repressors to induce degradation of the JAZs through the 26S proteasome pathway in a COI1-dependent manner. To reveal the formation process of COI1-JA-JAZ ternary complex, we employed several biochemical approaches to examine how JA is dynamically perceived. These analyses showed that the COI1 proteins of Arabidopsis and rice bind JA with appreciable binding affinity and revealed the kinetics and thermodynamics of the COI1-JA-JAZ ternary complex. Our results suggest that COI1 is the primary receptor perceiving the active JA molecule to initially form a COI1-JA complex that subsequently recruits JAZs for further signal transduction.