Biology subjects

Guan, R.

Publications and source records attributed to Guan, R..

28 records · Page 2Linked to original sources

bioRxiv2023

Structural mechanism of LIN28B nucleosome targeting by OCT4 for pluripotency

Pioneer transcription factors are essential for cell fate changes by targeting closed chromatin. OCT4 is a crucial pioneer factor that can induce cell reprogramming. However, the structural basis of how pioneer factors recognize the in vivo nucleosomal DNA targets is unknown. Here, we determine the high-resolution structures of the nucleosome containing human LIN28B DNA and its complexes with the OCT4 DNA binding region. Three OCT4s bind the pre-positioned nucleosome by recognizing non-canonical DNA motifs. Two use their POUS domains by forming extensive hydrogen bonds. The other uses the POUS-loop-POUHD region; POUHD serves as a wedge to unwrap [~]25 base pair DNA. Biochemical studies suggest that multiple OCT4s cooperatively open the H1-condensed nucleosome array containing the LIN28B nucleosome. Our study suggests a mechanism whereby OCT4s target the LIN28B nucleosome by forming multivalent interactions with nucleosomal motifs, unwrapping nucleosomal DNA, evicting H1, and cooperatively open closed chromatin to initiate cell reprogramming.

biophysics↗

bioRxiv2022

Tryptophan specialized metabolism and ER body-resident myrosinases modulate root microbiota assembly

Indole glucosinolates (IGs) are tryptophan (Trp)-derived sulfur-containing specialized metabolites that play a crucial role in plant-microbe interactions in plants of the order Brassicales, including Arabidopsis thaliana. Despite the growing body of evidence implicating IG biosynthetic pathways in root-microbiota interactions, how myrosinases, the enzymes that convert inert IGs into bioactive intermediate/terminal products, contribute to this process remains unknown. Here, we describe the roles of the PYK10 and BGLU21 myrosinases in root-microbiota assembly partly via metabolites secreted from roots into the rhizosphere. PYK10 and BGLU21 localize to the endoplasmic reticulum (ER) body, an ER-derived organelle observed in plants of the family Brassicaceae. We investigated the root microbiota structure of mutants defective in the Trp metabolic (cyp79b2b3 and myb34/51/122) and ER body (nai1 and pyk10bglu21) pathways and found that these factors together contribute to the assembly of root microbiota. Microbial community composition in soils as well as in bacterial synthetic communities (SynComs) treated with root exudates axenically collected from pyk10bglu21 and cyp79b2b3 differed significantly from those treated with exudates derived from wild-type plants, pointing to a direct role of root-exuded compounds. We also show that growth of the pyk10bglu21 and cyp79b2b3 mutants was severely inhibited by fungal endophytes isolated from healthy A. thaliana plants. Overall, our findings demonstrate that root ER body-resident myrosinases influencing the secretion of Trp-derived specialized metabolites represent a lineage-specific innovation that evolved in Brassicaceae to regulate root microbiota structure. SignificanceER bodies were first identified in roots of Brassicaceae plants more than 50 years ago, but their physiological functions have remained uncharacterized. A series of previous studies have suggested their possible role in root-microbe interactions. Here, we provide clear experimental evidence showing a role for ER bodies in root-microbiota interactions, which overlaps with that of root-exuded Trp-derived metabolites. Our findings delineate a plant lineage-specific innovation involving intracellular compartments and metabolic enzymes that evolved to regulate plant-microbe interactions at the root-soil interface.

plant biology↗

bioRxiv2022

Genome-wide signatures of geographic expansion and breeding process in soybean

The clarification of genomic signatures left during evolutionary histories of crops is crucial for breeding varieties adapting to changing climate. Soybean, a leguminous crop, provides both plant oil and protein. Here, we analyzed genome sequences of 2,214 soybeans and proposed its evolutionary route, which includes four geographic paths, expansion of annual wild soybean (Glycine soja Sieb. & Zucc.) from Southern China, domestication in Central China, expansion of landrace (G. max (L.) Merr.), and local breeding. We observed that local adaptation of the wild and cultivated soybeans was largely independent, and that genetic introgression was mostly derived from sympatric rather than allopatric wild populations during the range expansion of soybean landraces. Range expansion and breeding processes were accompanied with positive selection of flowering-time genes including GmSPA3c as validated by knock-out mutants. Our study shed lights on the evolutionary history of soybean and provides valuable genetic resources for future breeding. TeaserThe expansion and selection history of soybean

genomics↗

bioRxiv2021

GmSALT3 expression improves reactive oxygen species detoxification in salt-stressed soybean roots

Soybean plants are salinity (NaCl) sensitive, with their yield significantly decreased under moderately saline conditions. GmSALT3 is the dominant gene underlying a major QTL for salt tolerance in soybean. GmSALT3 encodes a transmembrane protein belonging to the plant cation/proton exchanger (CHX) family. It is currently unknown through which molecular mechanism(s) the ER-localised GmSALT3 contributes to salinity tolerance, as its localisation excludes direct involvement in ion exclusion. In order to gain insights into potential molecular mechanism(s), we used RNA-seq analysis of roots from two soybean NILs (Near Isogenic Lines); NIL-S (salt-sensitive, Gmsalt3) and NIL-T (salt-tolerant, GmSALT3), grown under control and saline conditions (200 mM NaCl) at three time points (0h, 6h, and 3 days). Gene ontology (GO) analysis showed that NIL-T has greater responses aligned to oxidation reduction. ROS were shown less abundant and scavenging enzyme activity was higher in NIL-T, consistent with the RNA-seq data. Further analysis indicated that genes related to calcium signalling, vesicle trafficking and Casparian strip (CS) development were upregulated in NIL-T following salt treatment. We propose that GmSALT3 improves the ability of NIL-T to cope with saline stress through preventing ROS overaccumulation in roots, and potentially modulating Ca2+ signalling, vesicle trafficking and formation of diffusion barriers. HighlightRNA-seq analysis revealed that GmSALT3, which confers improved salt tolerance on soybean, improves reactive oxygen species detoxification in roots.

plant biology↗

bioRxiv2021

Characterization of the Chlamydomonas reinhardtii phycosphere reveals conserved features of the plant microbiota

Microscopic algae release organic compounds to the region immediately surrounding their cells, known as the phycosphere, constituting a niche for colonization by heterotrophic bacteria. These bacteria take up algal photoassimilates and provide beneficial functions to their host, in a process that resembles the establishment of microbial communities associated with the roots and rhizospheres of land plants. Here, we characterize the microbiota of the model alga Chlamydomonas reinhardtii and reveal extensive taxonomic and functional overlap with the root microbiota of land plants. Reconstitution experiments using synthetic communities derived from C. reinhardtii and Arabidopsis thaliana show that phycosphere and root bacteria assemble into taxonomically equivalent communities on either host. We show that provision of diffusible metabolites is not sufficient for phycosphere community establishment, which additionally requires physical proximity to the host. Our data suggests that the microbiota of photosynthetic organisms, including green algae and flowering plants, assembles according to core ecological principles.

microbiology↗

bioRxiv2021

Host preference and invasiveness of commensals in the Lotus and Arabidopsis root microbiota

Healthy plants are colonized by microorganisms from the surrounding environment, which form stable communities and provide beneficial services to the host. Culture-independent profiling of the bacterial root microbiota shows that different plant species are colonized by distinct bacterial communities, even if they share the same habitat. It is, however, not known to what extent the host actively selects these communities and whether commensal bacteria are adapted to a specific plant species. Here, we report a sequence-indexed culture collection from roots and nodules of the model legume Lotus japonicus that contains representatives from the majority of species found in culture-independent profiles. Using taxonomically paired synthetic communities from L. japonicus and the crucifer Arabidopsis thaliana in a multi-species gnotobiotic system, we detect clear signatures of host preference among commensal bacteria in a community context, but not in mono-associations. Sequential inoculation of either host reveals strong priority effects during the assembly of the root microbiota, where established communities are resilient to invasion by late-comers. However, we found that host preference by commensal bacteria confers a competitive advantage in their native host. We reveal that host preference is prevalent in commensal bacteria from diverse taxonomic groups and that this trait is directly linked to their invasiveness into standing root-associated communities.

plant biology↗

bioRxiv2020

GmSALT3 confers shoot Na+ and Cl- exclusion in soybean via two distinct processes.

Soybean (Glycine max) yields are threatened by multiple stresses including soil salinity. GmSALT3 confers net shoot exclusion for both Na+ and Cl- and improves salt tolerance of soybean; however, how the ER-localised GmSALT3 achieves this is unknown. Here, GmSALT3s function was investigated in heterologous systems and near-isogenic lines that contained the full-length GmSALT3 (NIL-T; salt-tolerant) or a truncated transcript Gmsalt3 (NIL-S; salt-sensitive). GmSALT3 restored growth of K+-uptake-defective E. coli and contributed toward net influx and accumulation of Na+, K+, and Cl- in Xenopus laevis oocytes, while Gmsalt3 was non-functional. A time-course analysis of the NILs confirmed that shoot Cl- exclusion breaks down prior to Na+ exclusion, while grafting showed that shoot Na+ exclusion occurs via a root xylem-based mechanism. In contrast, NIL-T plants exhibited significantly greater Cl- content in both the stem xylem and phloem sap compared to NIL-S, indicating that shoot Cl- exclusion likely depends upon novel phloem-based Cl- recirculation. NIL-T shoots grafted on NIL-S roots contained low shoot Cl-, which confirmed that Cl- recirculation is dependent on the presence of GmSALT3 in shoots. Overall, these findings provide new insights on GmSALT3s impact on salinity tolerance and reveal a novel mechanism for shoot Cl- exclusion in plants. HighlightGmSALT3 improves soybean salt tolerance. Here, using heterologous expression, we found GmSALT3 is a functional ion transporter, and, in planta that it confers shoot salt exclusion through root-based Na+ xylem exclusion and shoot-based Cl- exclusion via phloem derived Cl- recirculation.

plant biology↗

bioRxiv2019

Protocol development for discovery of angiogenesis inhibitors via automated methods using zebrafish

Their optical clarity as larvae and embryos, small size, and high fecundity make zebrafish ideal for whole animal high throughput screening. A high-throughput drug discovery platform (HTP) has been built to perform fully automated screens of compound libraries with zebrafish embryos. A Tg(Flk1:EGFP) line, marking endothelial cell cytoplasm, was used in this work to help develop protocols and functional algorithms for the system, with the intent of screening for angiogenesis inhibitors. Indirubin 3 Monoxime (I3M), a known angiogenesis inhibitor, was used at various concentrations to validate the protocols. Consistent with previous studies, a dose dependant inhibitory effect of I3M on angiogenesis was confirmed. The methods and protocols developed here could significantly increase the throughput of drug screens, while limiting human errors. These methods are expected to facilitate the discovery of novel anti-angiogenesis compounds and can be adapted for many other applications in which samples have a good fluorescent signal.

developmental biology↗

bioRxiv2018

Comparison of antioxidant activity between cyanidin-3-O-glucoside (C3G) liposome and cyanidin-3-O-glucoside (C3G) in 2D and 3D cell cultures

The 2D cell culture is the predominant in vitro model for numerous studies. However, 2D cell cultures may not accurately reflect the functions of three-dimensional (3D) tissues, which have extensive cell-cell and cell-matrix interactions; thus, using 2D cell cultures may lead to inaccurate experimental results. Therefore, to obtain adequate and detailed information about the antioxidant activity of cyanidin-3-O-glucoside (C3G) and C3G liposomes in the 2D and 3D cell culture models, we used in this study H2O2 to construct the cell damage model and assess the antioxidant activity of C3G and C3G liposomes on Caco-2 cells cultured in the 3D model. We also measured the cell viability, cell morphology, and activity of glutathione (GSH), superoxide dismutase (SOD), total antioxidant capacity (T-AOC), and malondialdehyde (MDA) content of Caco-2 cells treated with H2O2, C3G, and C3G liposomes. Results showed that cells cultured in the 3D culture model formed a 3D structure and tight spheroids and showed increased cell activity and IC50. The C3G and C3G liposomes can enhance the activity of GSH, SOD, and T-AOC but decrease the MDA content. At the same time, the effect was more obvious in the 3D cell culture model than in the cells cultured in the 2D model. This study revealed that the results obtained from the 2D cell model may be inaccurate compared with the results obtained from the 3D cell model. A realistic mechanism study of antioxidant activity of C3G and C3G liposomes in the 3D cell model, which acts as an intermediate stage bridging the in vitro 2D and in vivo models, was observed.

cell biology↗

bioRxiv2018

Super-resolution tracking of mitochondrial dynamics with a third-row transition metal complex dye

Combining luminescent transition metal complex (LTMC) with super-resolution microscopy is an excellent strategy for the long-term visualization of the dynamics of subcellular structures in living cells. However, it remains unclear whether iridium(III) complexes are applicable for a particular type of super-resolution technique, structured illumination microscopy (SIM), to image subcellular structures.\n\nAs described herein, we developed an iridium(III) dye, to track mitochondrial dynamics in living cells under SIM. The dye demonstrated excellent specificity and photostability and satisfactory cell permeability. While using SIM to image mitochondria, we achieved an approximately 80-nm resolution that allowed the clear observation of the structure of mitochondrial cristae. We used the dye to monitor and quantify mitochondrial dynamics relative to lysosomes, including fusion involved in mitophagy, and newly discovered mitochondria-lysosome contact (MLC) under different conditions. MLC remained intact and fusion vanished when five receptors, p62, NDP52, OPTN, NBR1, and TAX1BP1, were knocked out, suggesting that these two processes are independence.

biophysics↗