Low CO2 concentration, a key environmental factor for developing plateau adapted rapeseed.

BACKGROUND: Photosynthesis is a fundamental process that underlies the formation of crop yield, wherein light serves as the driving force and carbon dioxide (CO2) as the raw material. These two factors have a direct influence on the progress and efficiency of photosynthesis in crops. Rapeseed is one of the four major oilseed crops worldwide. Plateau rapeseed has now become a research hotspot. However, the lack of high-yielding rapeseed germplasm resources on the plateau and the highly efficient strategy for screening them severely affect the development of rapeseed industry in plateau. RESULTS: In the rapeseed experimental fields located on the plateau (Lhasa, Tibet), we measured abundant sunlight, characterized by an average daily photosynthetically active radiation (PAR) of 1413 µmol m-2 s-1. In addition, the atmospheric CO2 concentrations range from 300 to 400 ppm, which is only two-thirds of that in the plain (Chengdu, Sichuan). We found that under different measurement conditions of light intensity and CO2 concentration, different rapeseed genotypes showed significant differences in leaf photosynthetic efficiency during the seedling stage. Moreover, the rapeseed materials with high photosynthetic efficiency under low CO2 concentrations rather than high light intensity, exhibited significant advantages in biomass, yield, and oil content when cultivated on the plateau, indicating that the CO2 is the key environmental factor which limited rapeseed production in plateau. Based on photosynthetic efficiency screening under low CO2 concentrations, six rapeseed varieties SC3, SC10, SC25, SC27, SC29 and SC37, shown significantly higher yields in plateau environment compared to local control variety were obtained. In addition, the adaptability of rapeseed to plateau was found to be related to the activities of key Calvin cycle enzymes and the accumulation of photosynthetic products. CONCLUSIONS: This study established a screening strategy for plateau high-yielding rapeseed materials, obtained six varieties which were suitable for plateau cultivation, explored the mechanism of rapeseed response to the plateau environment, and thus provides a feasible strategy for plateau-adapted rapeseed breeding.

A plant cytorhabdovirus modulates locomotor activity of insect vectors to enhance virus transmission.

Transmission of many plant viruses relies on phloem-feeding insect vectors. However, how plant viruses directly modulate insect behavior is largely unknown. Barley yellow striate mosaic virus (BYSMV) is transmitted by the small brown planthopper (SBPH, Laodelphax striatellus). Here, we show that BYSMV infects the central nervous system (CNS) of SBPHs, induces insect hyperactivity, and prolongs phloem feeding duration. The BYSMV accessory protein P6 interacts with the COP9 signalosome subunit 5 (LsCSN5) of SBPHs and suppresses LsCSN5-regulated de-neddylation from the Cullin 1 (CUL1), hereby inhibiting CUL1-based E3 ligases-mediated degradation of the circadian clock protein Timeless (TIM). Thus, virus infection or knockdown of LsCSN5 compromises TIM oscillation and induces high insect locomotor activity for transmission. Additionally, expression of BYSMV P6 in the CNS of transgenic Drosophila melanogaster disturbs circadian rhythm and induces high locomotor activity. Together, our results suggest the molecular mechanisms whereby BYSMV modulates locomotor activity of insect vectors for transmission.

A Bayesian joint model for compositional mediation effect selection in microbiome data.

Analyzing multivariate count data generated by high-throughput sequencing technology in microbiome research studies is challenging due to the high-dimensional and compositional structure of the data and overdispersion. In practice, researchers are often interested in investigating how the microbiome may mediate the relation between an assigned treatment and an observed phenotypic response. Existing approaches designed for compositional mediation analysis are unable to simultaneously determine the presence of direct effects, relative indirect effects, and overall indirect effects, while quantifying their uncertainty. We propose a formulation of a Bayesian joint model for compositional data that allows for the identification, estimation, and uncertainty quantification of various causal estimands in high-dimensional mediation analysis. We conduct simulation studies and compare our method's mediation effects selection performance with existing methods. Finally, we apply our method to a benchmark data set investigating the sub-therapeutic antibiotic treatment effect on body weight in early-life mice.

Editing of a Novel Cd Uptake-Related Gene CUP1 Contributes to Reducing Cd Accumulations in Arabidopsis thaliana and Brassica napus.

Brassica napus is a Cd hyperaccumulator, which is a serious threat to food and fodder safety. However, no related studies on developing Cd-safe B. napus have been reported yet. Here, we screened out a novel Cd uptake-related gene, AtCUP1, from the major facilitator superfamily in Arabidopsis thaliana. The mutation of AtCUP1 decreased Cd accumulation, both in roots and shoots of A. thaliana. Furthermore, the disruption of the AtCUP1 gene by the CRISPR/Cas9 system significantly reduced Cd accumulation in A. thaliana. Interestingly, the disruption of the BnCUP1 gene, an orthologous gene of AtCUP1, by the CRISPR/Cas9 system also diminished Cd accumulation in both roots and shoots of B. napus based on the hydroponics assay. Furthermore, for the field experiment, the Cd accumulations of BnCUP1-edited lines were reduced by 52% in roots and 77% in shoots compared to that of wild-type (WT) lines, and the biomass and yield of BnCUP1-edited lines increased by 42% and 47% of that of WT, respectively. Noteworthily, agronomic characteristics of B. napus were not apparently affected by BnCUP1-editing. Thus, BnCUP1-edited lines are excellent non-transgenic germplasm resources for reducing Cd accumulation without a distinct compromise in yield, which could be applied to agricultural production in Cd-contaminated soils.

Nine-fold symmetry of centriole: The joint efforts of its core proteins.

The centriole is a widely conserved organelle required for the assembly of centrosomes, cilia, and flagella. Its striking feature - the nine-fold symmetrical structure, was discovered over 70 years ago by transmission electron microscopy, and since elaborated mostly by cryo-electron microscopy and super-resolution microscopy. Here, we review the discoveries that led to the current understanding of how the nine-fold symmetrical structure is built. We focus on the recent findings of the centriole structure in high resolution, its assembly pathways, and its nine-fold distributed components. We propose a model that the assembly of the nine-fold symmetrical centriole depends on the concerted efforts of its core proteins. Also see the video abstract here: https://youtu.be/m4h_3II_WJo.

Bone health in spacefaring rodents and primates: systematic review and meta-analysis.

Animals in space exploration studies serve both as a model for human physiology and as a means to understand the physiological effects of microgravity. To quantify the microgravity-induced changes to bone health in animals, we systematically searched Medline, Embase, Web of Science, BIOSIS, and NASA Technical reports. We selected 40 papers focusing on the bone health of 95 rats, 61 mice, and 9 rhesus monkeys from 22 space missions. The percentage difference from ground control in rodents was -24.1% [Confidence interval: -43.4, -4.9] for trabecular bone volume fraction and -5.9% [-8.0, -3.8] for the cortical area. In primates, trabecular bone volume fraction was lower by -25.2% [-35.6, -14.7] in spaceflight animals compared to GC. Bone formation indices in rodent trabecular and cortical bone were significantly lower in microgravity. In contrast, osteoclast numbers were not affected in rats and were variably affected in mice. Thus, microgravity induces bone deficits in rodents and primates likely through the suppression of bone formation.

Superresolution characterization of core centriole architecture.

The centrosome is the main microtubule-organizing center in animal cells. It comprises of two centrioles and the surrounding pericentriolar material. Protein organization at the outer layer of the centriole and outward has been studied extensively; however, an overall picture of the protein architecture at the centriole core has been missing. Here we report a direct view of Drosophila centriolar proteins at ∼50-nm resolution. This reveals a Sas6 ring at the C-terminus, where it overlaps with the C-terminus of Cep135. The ninefold symmetrical pattern of Cep135 is further conveyed through Ana1-Asterless axes that extend past the microtubule wall from between the blades. Ana3 and Rcd4, whose termini are close to Cep135, are arranged in ninefold symmetry that does not match the above axes. During centriole biogenesis, Ana3 and Rcd4 are sequentially loaded on the newly formed centriole and are required for centriole-to-centrosome conversion through recruiting the Cep135-Ana1-Asterless complex. Together, our results provide a spatiotemporal map of the centriole core and implications of how the structure might be built.

CEP290 is essential for the initiation of ciliary transition zone assembly.

Cilia play critical roles during embryonic development and adult homeostasis. Dysfunction of cilia leads to various human genetic diseases, including many caused by defects in transition zones (TZs), the "gates" of cilia. The evolutionarily conserved TZ component centrosomal protein 290 (CEP290) is the most frequently mutated human ciliopathy gene, but its roles in ciliogenesis are not completely understood. Here, we report that CEP290 plays an essential role in the initiation of TZ assembly in Drosophila. Mechanistically, the N-terminus of CEP290 directly recruits DAZ interacting zinc finger protein 1 (DZIP1), which then recruits Chibby (CBY) and Rab8 to promote early ciliary membrane formation. Complete deletion of CEP290 blocks ciliogenesis at the initiation stage of TZ assembly, which can be mimicked by DZIP1 deletion mutants. Remarkably, expression of the N-terminus of CEP290 alone restores the TZ localization of DZIP1 and subsequently ameliorates the defects in TZ assembly initiation in cep290 mutants. Our results link CEP290 to DZIP1-CBY/Rab8 module and uncover a previously uncharacterized important function of CEP290 in the coordination of early ciliary membrane formation and TZ assembly.

Aurora B regulates PP1γ-Repo-Man interactions to maintain the chromosome condensation state.

The mitotic kinase Aurora B regulates the condensation of chromatin into chromosomes by phosphorylating chromatin proteins during early mitosis, whereas the phosphatase PP1γ performs the opposite function. The roles of Aurora B and PP1γ must be tightly coordinated to maintain chromosomes at a high phosphorylation state, but the precise mechanisms regulating their function remain largely unclear. Here, mainly through immunofluorescence microscopy and co-immunoprecipitation assays, we find that dissociation of PP1γ from chromosomes is essential for maintaining chromosome phosphorylation. We uncover that PP1γ is recruited to mitotic chromosomes by its regulatory subunit Repo-Man in the absence of Aurora B activity and that Aurora B regulates dissociation of PP1γ by phosphorylating and disrupting PP1γ-Repo-Man interactions on chromatin. Overexpression of Repo-Man mutants that cannot be phosphorylated or inhibition of Aurora B kinase activity resulted in the retention of PP1γ on chromatin and prolonged the chromatin condensation process; a similar outcome was caused by the ectopic targeting of PP1γ to chromatin. Together, our findings reveal a novel regulation mechanism of chromatin condensation in which Aurora B counteracts PP1γ activity by releasing PP1γ from Repo-Man and may have important implications for understanding the regulations of dynamic structural changes of the chromosomes in mitosis.

DNA replication licensing factor Cdc6 and Plk4 kinase antagonistically regulate centrosome duplication via Sas-6.

Centrosome number is tightly controlled during the cell cycle to ensure proper spindle assembly and cell division. However, the underlying mechanism that controls centrosome number remains largely unclear. We show herein that the DNA replication licensing factor Cdc6 is recruited to the proximal side of the centrioles via cyclin A to negatively regulate centrosome duplication by binding and inhibiting the cartwheel protein Sas-6 from forming a stable complex with another centriole duplication core protein, STIL. We further demonstrate that Cdc6 colocalizes with Plk4 at the centrosome, and interacts with Plk4 during S phase. Plk4 disrupts the interaction between Sas-6 and Cdc6, and suppresses the inhibitory role of Cdc6 on Sas-6 by phosphorylating Cdc6. Overexpressing wild-type Cdc6 or Plk4-unphosphorylatable Cdc6 mutant 2A reduces centrosome over-duplication caused by Plk4 overexpression or hydroxyurea treatment. Taken together, our data demonstrate that Cdc6 and Plk4 antagonistically control proper centrosome duplication during the cell cycle.

Conserved molecular interactions in centriole-to-centrosome conversion.

Centrioles are required to assemble centrosomes for cell division and cilia for motility and signalling. New centrioles assemble perpendicularly to pre-existing ones in G1-S and elongate throughout S and G2. Fully elongated daughter centrioles are converted into centrosomes during mitosis to be able to duplicate and organize pericentriolar material in the next cell cycle. Here we show that centriole-to-centrosome conversion requires sequential loading of Cep135, Ana1 (Cep295) and Asterless (Cep152) onto daughter centrioles during mitotic progression in both Drosophila melanogaster and human. This generates a molecular network spanning from the inner- to outermost parts of the centriole. Ana1 forms a molecular strut within the network, and its essential role can be substituted by an engineered fragment providing an alternative linkage between Asterless and Cep135. This conserved architectural framework is essential for loading Asterless or Cep152, the partner of the master regulator of centriole duplication, Plk4. Our study thus uncovers the molecular basis for centriole-to-centrosome conversion that renders daughter centrioles competent for motherhood.

TPX2 phosphorylation maintains metaphase spindle length by regulating microtubule flux.

A steady-state metaphase spindle maintains constant length, although the microtubules undergo intensive dynamics. Tubulin dimers are incorporated at plus ends of spindle microtubules while they are removed from the minus ends, resulting in poleward movement. Such microtubule flux is regulated by the microtubule rescue factors CLASPs at kinetochores and depolymerizing protein Kif2a at the poles, along with other regulators of microtubule dynamics. How microtubule polymerization and depolymerization are coordinated remains unclear. Here we show that TPX2, a microtubule-bundling protein and activator of Aurora A, plays an important role. TPX2 was phosphorylated by Aurora A during mitosis. Its phospho-null mutant caused short metaphase spindles coupled with low microtubule flux rate. Interestingly, phosphorylation of TPX2 regulated its interaction with CLASP1 but not Kif2a. The effect of its mutant in shortening the spindle could be rescued by codepletion of CLASP1 and Kif2a that abolished microtubule flux. Together we propose that Aurora A-dependent TPX2 phosphorylation controls mitotic spindle length through regulating microtubule flux.

Spatial Compartmentalization Specializes the Function of Aurora A and Aurora B.

Aurora kinase A and B share great similarity in sequences, structures, and phosphorylation motif, yet they show different localizations and play distinct crucial roles. The factors that determine such differences are largely unknown. Here we targeted Aurora A to the localization of Aurora B and found that Aurora A phosphorylates the substrate of Aurora B and substitutes its function in spindle checkpoint. In return, the centrosome targeting of Aurora B substitutes the function of Aurora A in the mitotic entry. Expressing the chimera proteins of the Auroras with exchanged N termini in cells indicates that the divergent N termini are also important for their spatiotemporal localizations and functions. Collectively, we demonstrate that functional divergence of Aurora kinases is determined by spatial compartmentalization, and their divergent N termini also contribute to their spatial and functional differentiation.

The centrosome and its duplication cycle.

The centrosome was discovered in the late 19th century when mitosis was first described. Long recognized as a key organelle of the spindle pole, its core component, the centriole, was realized more than 50 or so years later also to comprise the basal body of the cilium. Here, we chart the more recent acquisition of a molecular understanding of centrosome structure and function. The strategies for gaining such knowledge were quickly developed in the yeasts to decipher the structure and function of their distinctive spindle pole bodies. Only within the past decade have studies with model eukaryotes and cultured cells brought a similar degree of sophistication to our understanding of the centrosome duplication cycle and the multiple roles of this organelle and its component parts in cell division and signaling. Now as we begin to understand these functions in the context of development, the way is being opened up for studies of the roles of centrosomes in human disease.

Plk4 phosphorylates Ana2 to trigger Sas6 recruitment and procentriole formation.

Centrioles are 9-fold symmetrical structures at the core of centrosomes and base of cilia whose dysfunction has been linked to a wide range of inherited diseases and cancer. Their duplication is regulated by a protein kinase of conserved structure, the C. elegans ZYG-1 or its Polo-like kinase 4 (Plk4) counterpart in other organisms. Although Plk4's centriolar partners and mechanisms that regulate its stability are known, its crucial substrates for centriole duplication have never been identified. Here we show that Drosophila Plk4 phosphorylates four conserved serines in the STAN motif of the core centriole protein Ana2 to enable it to bind and recruit its Sas6 partner. Ana2 and Sas6 normally load onto both mother and daughter centrioles immediately after their disengagement toward the end of mitosis to seed procentriole formation. Nonphosphorylatable Ana2 still localizes to the centriole but can no longer recruit Sas6 and centriole duplication fails. Thus, following centriole disengagement, recruitment of Ana2 and its phosphorylation by Plk4 are the earliest known events in centriole duplication to recruit Sas6 and thereby establish the architecture of the new procentriole engaged with its parent.

Spindle formation in the mouse embryo requires Plk4 in the absence of centrioles.

During the first five rounds of cell division in the mouse embryo, spindles assemble in the absence of centrioles. Spindle formation initiates around chromosomes, but the microtubule nucleating process remains unclear. Here we demonstrate that Plk4, a protein kinase known as a master regulator of centriole formation, is also essential for spindle assembly in the absence of centrioles. Depletion of maternal Plk4 prevents nucleation and growth of microtubules and results in monopolar spindle formation. This leads to cytokinesis failure and, consequently, developmental arrest. We show that Plk4 function depends on its kinase activity and its partner protein, Cep152. Moreover, tethering Cep152 to cellular membranes sequesters Plk4 and is sufficient to trigger spindle assembly from ectopic membranous sites. Thus, the Plk4-Cep152 complex has an unexpected role in promoting microtubule nucleation in the vicinity of chromosomes to mediate bipolar spindle formation in the absence of centrioles.

Structured illumination of the interface between centriole and peri-centriolar material.

The increase in centrosome size in mitosis was described over a century ago, and yet it is poorly understood how centrioles, which lie at the core of centrosomes, organize the pericentriolar material (PCM) in this process. Now, structured illumination microscopy reveals in Drosophila that, before clouds of PCM appear, its proteins are closely associated with interphase centrioles in two tube-like layers: an inner layer occupied by centriolar microtubules, Sas-4, Spd-2 and Polo kinase; and an outer layer comprising Pericentrin-like protein (Dplp), Asterless (Asl) and Plk4 kinase. Centrosomin (Cnn) and γ-tubulin associate with this outer tube in G2 cells and, upon mitotic entry, Polo activity is required to recruit them together with Spd-2 into PCM clouds. Cnn is required for Spd-2 to expand into the PCM during this maturation process but can itself contribute to PCM independently of Spd-2. By contrast, the centrioles of spermatocytes elongate from a pre-existing proximal unit during the G2 preceding meiosis. Sas-4 is restricted to the microtubule-associated, inner cylinder and Dplp and Cnn to the outer cylinder of this proximal part. γ-Tubulin and Asl associate with the outer cylinder and Spd-2 with the inner cylinder throughout the entire G2 centriole. Although they occupy different spatial compartments on the G2 centriole, Cnn, Spd-2 and γ-tubulin become diminished at the centriole upon entry into meiosis to become part of PCM clouds.

Chromatin-bound NLS proteins recruit membrane vesicles and nucleoporins for nuclear envelope assembly via importin-α/ß.

The mechanism for nuclear envelope (NE) assembly is not fully understood. Importin-ß and the small GTPase Ran have been implicated in the spatial regulation of NE assembly process. Here we report that chromatin-bound NLS (nuclear localization sequence) proteins provide docking sites for the NE precursor membrane vesicles and nucleoporins via importin-α and -ß during NE assembly in Xenopus egg extracts. We show that along with the fast recruitment of the abundant NLS proteins such as nucleoplasmin and histones to the demembranated sperm chromatin in the extracts, importin-α binds the chromatin NLS proteins rapidly. Meanwhile, importin-ß binds cytoplasmic NE precursor membrane vesicles and nucleoporins. Through interacting with importin-α on the chromatin NLS proteins, importin-ß targets the membrane vesicles and nucleoporins to the chromatin surface. Once encountering Ran-GTP on the chromatin generated by RCC1, importin-ß preferentially binds Ran-GTP and releases the membrane vesicles and nucleoporins for NE assembly. NE assembly is disrupted by blocking the interaction between importin-α and NLS proteins with excess soluble NLS proteins or by depletion of importin-ß from the extract. Our findings reveal a novel molecular mechanism for NE assembly in Xenopus egg extracts.

Klp10A, a microtubule-depolymerizing kinesin-13, cooperates with CP110 to control Drosophila centriole length.

Klp10A is a kinesin-13 of Drosophila melanogaster that depolymerizes cytoplasmic microtubules. In interphase, it promotes microtubule catastrophe; in mitosis, it contributes to anaphase chromosome movement by enabling tubulin flux. Here we show that Klp10A also acts as a microtubule depolymerase on centriolar microtubules to regulate centriole length. Thus, in both cultured cell lines and the testes, absence of Klp10A leads to longer centrioles that show incomplete 9-fold symmetry at their ends. These structures and associated pericentriolar material undergo fragmentation. We also show that in contrast to mammalian cells where depletion of CP110 leads to centriole elongation, in Drosophila cells it results in centriole length diminution that is overcome by codepletion of Klp10A to give longer centrioles than usual. We discuss how loss of centriole capping by CP110 might have different consequences for centriole length in mammalian and insect cells and also relate these findings to the functional interactions between mammalian CP110 and another kinesin-13, Kif24, that in mammalian cells regulates cilium formation.