全反式维甲酸对骺软骨细胞生物学行为及其功能影响的研究

该研究主要探讨了体外高浓度全反式维甲酸(all-trans retinoic acid,ATRA)对SD大鼠骺软骨细胞生物学性状和功能的影响以及体内ATRA对SD大鼠胫骨生长板的影响。以SD大鼠骺软骨细胞为研究对象、ATRA为干预因素,采用CCK-8、细胞流式术、HE染色、Annexin V-FITC细胞凋亡流式检测术、Hoechst染色、细胞划痕、Transwell实验分别评估ATRA处理后细胞的增殖、周期、形态、凋亡及迁移情况,Western blot检测蛋白聚糖、Ⅱ型胶原、X型胶原等相关功能蛋白的变化;以3周雄性SD大鼠为实验对象,分为对照组、60 mg/kg·d ATRA组、80 mg/kg·d ATRA组,进行10天连续ATRA灌胃处理,测量每只SD大鼠灌胃第1天、第10天的头尾长,处理10天后对胫骨生长板进行HE染色。结果表明,ATRA作用SD大鼠骺软骨细胞后,增殖能力减弱且细胞周期被阻滞在S期(P<0.01),细胞形态由三角形、多边形变为长条状,凋亡的发生增多(P<0.01),迁移能力受到抑制(P<0.05)以及Western blot结果显示蛋白聚糖、Ⅱ型胶原、X型胶原等功能相关蛋白较对照组表达均明显降低(P<0.01);对SD大鼠进行ATRA灌胃处理后,与对照组比较,60 mg/kg·d ATRA组和80 mg/kg·d ATRA组的头尾长均变短(P<0.01);胫骨生长板HE染色显示,ATRA灌胃组的生长板变窄甚至闭合。该研究证实了体外高浓度ATRA能够对SD大鼠骺软骨细胞的增殖、迁移起抑制作用,同时能够诱导凋亡,降低相关功能蛋白的表达,在SD大鼠体内证实,过量ATRA可影响生长板软骨内成骨过程,最终使生长板部分或全部提前闭合,进而影响SD大鼠身长的增长。     

Elevated intracellular cyclic-di-GMP level in Shewanella oneidensis increases expression of c-type cytochromes

Electrochemically active biofilms are capable of exchanging electrons with solid electron acceptors and have many energy and environmental applications such as bioelectricity generation and environmental remediation. The performance of electrochemically active biofilms is usually dependent on c-type cytochromes, while biofilm development is controlled by a signal cascade mediated by the intracellular secondary messenger bis-(3ʹ-5ʹ) cyclic dimeric guanosine monophosphate (c-di-GMP). However, it is unclear whether there are any links between the c-di-GMP regulatory system and the expression of c-type cytochromes. In this study, we constructed a S. oneidensis MR-1 strain with a higher cytoplasmic c-di-GMP level by constitutively expressing a c-di-GMP synthase and it exhibited expected c-di-GMP-influenced traits, such as lowered motility and increased biofilm formation. Compared to MR-1 wild-type strain, the high c-di-GMP strain had a higher Fe(III) reduction rate (21.58 vs 11.88 pM of Fe(III)/h cell) and greater expression of genes that code for the proteins involved in the Mtr pathway, including CymA, MtrA, MtrB, MtrC and OmcA. Furthermore, single-cell Raman microspectroscopy (SCRM) revealed a great increase of c-type cytochromes in the high c-di-GMP strain as compared to MR-1 wild-type strain. Our results reveal for the first time that the c-di-GMP regulation system indirectly or directly positively regulates the expression of cytochromes involved in the extracellular electron transport (EET) in S. oneidensis, which would help to understand the regulatory mechanism of c-di-GMP on electricity production in bacteria.     

Depth‐dependent soil organic carbon dynamics of croplands across the Chengdu Plain of China from the 1980s to the 2010s

Agricultural soils have tremendous potential to sequester soil organic carbon (SOC) and mitigate global climate change. However, agricultural land use has a profound impact on SOC dynamics, and few studies have explored how agricultural land use combined with soil conditions affect SOC changes throughout the soil profile. Based on a paired soil resampling campaign in the 1980s and 2010s, this study investigated the SOC changes of the soil profile caused by agricultural land use and the correlations with parent material and topography across the Chengdu Plain of China. The results showed that the SOC content increased by 3.78 g C/kg in the topsoil (0–20 cm), but decreased in the 20–40 cm and 40–60 cm soil layers by 0.90 and 1.26 g C/kg respectively. SOC increases in topsoil were observed for all types of agricultural land. Afforestation on former agricultural land also caused SOC decreases in the 20–60 cm soil layers, while SOC decreases only occurred in the 40–60 cm soil layer for agricultural land using a traditional crop rotation (i.e. traditional rice–wheat/rapeseed rotation) and with rice–vegetable rotations converted from the traditional rotations. For each agricultural land use, SOC decreases in deep soils only occurred in high relief areas and in soils formed from Q4 (Quaternary Holocene) grey‐brown alluvium and Q4 grey alluvium that had a relatively low soil bulk density and clay content. The results indicated that SOC change caused by agricultural land use was depth dependent and that the effects of agricultural land use on soil profile SOC dynamics varied with soil characteristics and topography. Subsoil SOC decreases were more likely to occur in high relief areas and in soils with low soil bulk density and low clay content.     

Quorum sensing regulation confronts the development of a viable but non-culturable state in Vibrio cholerae

Vibrio cholerae can enter a viable but non-culturable (VBNC) state when it encounters unfavourable environments; VBNC cells serve as important reservoirs and still pose threats to public health. The genetic regulation of V. cholerae entering its VBNC state is not well understood. Here, we show a confrontation strategy adapted by V. cholerae O1 in which it utilizes a quorum sensing (QS) system to prevent transition into a VBNC state under low nutrition and temperature conditions. The upregulation of hapR resulted in a prolonged culturable state of V. cholerae in artificial sea water at 4°C, whereas the mutation of hapR led to fast entry into the VBNC state. We also observed that different V. cholerae O1 natural isolates with distinct QS functions present a variety of abilities to maintain culturability during the transition to a VBNC state. The strain groups with higher or constitutive expression of QS genes exhibit a greater tendency to maintain the culturable state during VBNC induction than those lacking QS functional groups. In summary, HapR-mediated QS regulation is associated with the transition to the VBNC state in V. cholerae. HapR expression causes V. cholerae to resist VBNC induction and become dominant over competitors in changing environments.     

Soil and root nutrient chemistry structure root-associated fungal assemblages in temperate forests

Root-associated fungi (RAF) link nutrient fluxes between soil and roots and thus play important roles in ecosystem functioning. To enhance our understanding of the factors that control RAF, we fitted statistical models to explain variation in RAF community structure using data from 150 temperate forest sites covering a broad range of environmental conditions and chemical root traits. We found that variation in RAF communities was related to both root traits (e.g., cations, carbohydrates, NO₃⁻) and soil properties (pH, cations, moisture, C/N). The identified drivers were the combined result of distinct response patterns of fungal taxa (determined at the rank of orders) to biotic and abiotic factors. Our results support that RAF community variation is related to evolutionary adaptedness of fungal lineages and consequently, drivers of RAF communities are context-dependent.     

The auxin-inducible phosphate transporter AsPT5 mediates phosphate transport and is indispensable for arbuscule formation in Chinese milk vetch at moderately high phosphate supply

Phosphorus is a macronutrient that is essential for plant survival. Most land plants have evolved the ability to form a mutualistic symbiosis with arbuscular mycorrhizal (AM) fungi, which enhances phosphate (Pi) acquisition. Modulation of Pi transporter systems is the master strategy used by mycorrhizal plants to adapt to ambient Pi concentrations. However, the specific functions of PHOSPHATE TRANSPORTER 1 (PHT1) genes, which are Pi transporters that are responsive to high Pi availability, are largely unknown. Here, we report that AsPT5, an Astragalus sinicus (Chinese milk vetch) member of the PHT1 gene family, is conserved across dicotyledons and is constitutively expressed in a broad range of tissues independently of Pi supply, but is remarkably induced by indole-3-acetic acid (auxin) treatment under moderately high Pi conditions. Subcellular localization experiments indicated that AsPT5 localizes to the plasma membrane of plant cells. Using reverse genetics, we showed that AsPT5 not only mediates Pi transport and remodels root system architecture but is also essential for arbuscule formation in A. sinicus under moderately high Pi concentrations. Overall, our study provides insight into the function of AsPT5 in Pi transport, AM development and the cross-talk between Pi nutrition and auxin signalling in mycorrhizal plants.     

PagR mediates the precise regulation of Salmonella pathogenicity island 2 gene expression in response to magnesium and phosphate signals in Salmonella Typhimurium

To establish systemic infections, Salmonella enterica serovar Typhimurium (S. Typhimurium) requires Salmonella pathogenicity island 2 (SPI‐2) to survive and replicate within macrophages. High expression of many SPI‐2 genes during the entire intracellular growth period within macrophages is essential, as it contributes to the formation of Salmonella‐containing vacuole and bacterial replication. However, the regulatory mechanisms underlying the sustained induction of SPI‐2 within macrophages are not fully understood. Here, we revealed a time‐dependent regulation of SPI‐2 expression mediated by a novel regulator PagR (STM2345) in response to the low Mg²⁺ and low phosphate (P_i) signals, which ensured the high induction of SPI‐2 during the entire intramacrophage growth period. Deletion of pagR results in reduced bacterial replication in macrophages and attenuation of systemic virulence in mice. The effects of pagR on virulence are dependent on upregulating the expression of slyA, a regulator of SPI‐2. At the early (0–4 hr) and later (after 4 hr) stage post‐infection of macrophages, pagR is induced by the low P_i via PhoB/R two‐component systems and low Mg²⁺ via PhoP/Q systems, respectively. Collectively, our findings revealed that the PagR‐mediated regulatory mechanism contributes to the precise and sustained activation of SPI‐2 genes within macrophages, which is essential for S. Typhimurium systemic virulence.