Spatial Regulation Research Articles

Recent progress in single atomic catalysts for electrochemical N2 fixation

Ammonia (NH3), as an important chemical product, is industrially produced using the traditional energy-intensive Haber-Bosch method at high temperature and pressure. Electrochemical nitrogen reduction reaction (NRR) to synthesize NH3 at ambient conditions has been considered as a promising candidate for replacing Haber-Bosch process. However, major obstacles, such as poor catalytic activity and selectivity and extensive competitive hydrogen evolution reaction, remain in NRR, which urgently need to be addressed. Single atom electrocatalysts (SACs) have attracted wide attention in view of their nearly 100% atomic utilization and outstanding catalytic performance. In this review, recent theoretical and experimental advances on novel atomically dispersed electrocatalysts for NRR are summarized and highlighted. We start with the fundamental reaction mechanism of NRR. Then, different preparation methods and the strategies of boosting catalytic performance of SACs from the aspects of coordination environment, coordination number, metal-support interaction and spatial microenvironment regulation are presented and analyzed in detail. Following this, the extensive applications of SACs in terms of noble metal based-SACs and transition metal-based SACs in NRR are discussed. Finally, we provide a perspective of the challenges of SACs for NRR, aiming to guide the rational design of advanced NRR catalysts.

Mass tourism generated urban land expansion in the catchment of Lake Balaton, Hungary – analysis of long-term changes in characteristic socio-political periods

Understanding changes in land use and land cover (LULC) is a prerequisite for the sustainable management of ecosystems, with implications for regulatory policy. In this study, we use a hierarchical approach to quantify long-term changes in LULC in the catchment of the largest Central-European shallow lake (Lake Balaton, Hungary). We evaluate changes over three centuries at the catchment and different spatial levels of the shoreline. Within this framework, we develop a methodology suitable for analysing land use transformations in the shoreline zone, typically affected by LULC changes stemming from mass tourism. Our findings indicate that LULC transformations at the catchment level were relatively minor compared to those observed along the shoreline, where urbanization driven by mass tourism emerged as a drivers of LULC changes. The dynamics of urbanization closely mirrored socio-political shifts and exhibited a strong dependence on distance from the shore. Temporal trajectories of LULC changes revealed that the most significant alterations occurred within the 0–500 m and 500–1000 m shoreline distance zones during the socialist era when the lake served as a focal point for tourism in Central and Eastern Europe. While the process of mass tourism-induced urbanization has declined significantly since the collapse of the socialist regime, the sprawl of urban (built up) areas into rural territories persist. Given the unregulated nature of urbanization at the forefront, we emphasize the importance for policy makers and local stakeholders to control further transformations of semi-natural and natural areas into built up areas along the shoreline. Achieving sustainable LULC management in lakes affected by mass tourism, such as Lake Balaton, necessitates robust legislative and administrative efforts in spatial planning and regulation. This endeavour should be pursued as a shared interest among residents and tourists alike.

A Ligand-Directed Spatial Regulation to Structural and Functional Tunability in Aggregation-Induced Emission Luminogen-Functionalized Organic-Inorganic Nanoassemblies.

Aggregation-induced emission luminogen (AIEgen)-functionalized organic-inorganic hybrid nanoparticles (OINPs) are an emerging category of multifunctional nanomaterials with vast potential applications. The spatial arrangement and positioning of AIEgens and inorganic compounds in AIEgen-functionalized OINPs determine the structures, properties, and functionalities of the self-assembled nanomaterials. In this work, a facile and general emulsion self-assembly tactic for synthesizing well-defined AIEgen-functionalized OINPs is proposed by coassembling alkane chain-functionalized inorganic nanoparticles with hydrophobic organic AIEgens. As a proof of concept, the self-assembly and structural evolution of plasmonic-fluorescent hybrid nanoparticles (PFNPs) from concentric circle to core shell and then to Janus structures is demonstrated by using alkane chain-modified AuNPs and AIEgens as building blocks. The spatial position of AuNPs in the signal nanocomposite is controlled by varying the alkane ligand length and density on the AuNP surface. The mechanism behind the formation of various PFNP nanostructures is also elucidated through experiments and theoretical simulation. The obtained PFNPs with diverse structures exhibit spatially tunable optical and photothermal properties for advanced applications in multicolor and multimode immunolabeling and photothermal sterilization. This work presents an innovative synthetic approach of constructing AIEgen-functionalized OINPs with diverse structures, compositions, and functionalities, thereby championing the progressive development of these OINPs.

Dynamics of Wnt/β-catenin reporter activity throughout whole life in a naturally short-lived vertebrate.

Wnt/β-catenin signaling plays a major role in regulation of embryogenesis, organogenesis, and adult tissue homeostasis and regeneration. However, the roles played by Wnt/β-catenin and the spatiotemporal regulation of its activity throughout life, including during aging, are not fully understood. To address these issues, we introduced a Wnt/β-catenin signaling sensitive reporter into African turquoise killifish (Nothobranchius furzeri), a naturally ultra-short-lived fish that allows for the analysis of its whole life within a short period of time. Using this reporter killifish, we unraveled the previously unidentified dynamics of Wnt/β-catenin signaling during development and aging. Using the reporter strain, we detected Wnt/β-catenin activity in actively developing tissues as reported in previous reports, but also observed activation and attenuation of Wnt/β-catenin activity during embryonic reaggregation and diapause, respectively. During the aging process, the reporter was activated in the choroidal layer and liver, but its expression decreased in the kidneys. In addition, the reporter also revealed that aging disrupts the spatial regulation and intensity control of Wnt/β-catenin activity seen during fin regeneration, which interferes with precise regeneration. Thus, the employed reporter killifish is a highly useful model for investigating the dynamics of Wnt/β-catenin signaling during both the developmental and aging process.

Drought Offsets the Controls on Colored Dissolved Organic Matter in Lakes

The concentration of colored dissolved organic matter (CDOM) in lakes is strongly influenced by climate, land cover, and topographic settings, but it is not known how drought may affect the relative importance of these controls. Here, we evaluate the controls of CDOM during two summers with strongly contrasting values of the Palmer drought index (PDI), indicating wet vs. dry conditions. We hypothesized that lake CDOM during a wet summer season is regulated mainly by the surrounding land cover to which the lakes are hydrologically connected, while, during drought, the lakes are disconnected from the catchment and CDOM is regulated by climatic and morphometric factors that govern the internal turnover of CDOM in the lakes. A suite of climate, land cover, and morphometric variables was assembled and used to explain remotely sensed CDOM values for 255 boreal lakes distributed across broad environmental and geographic gradients in Sweden and Norway. We found that PDI explained the variability in CDOM among lakes in a dry year, but not in a wet year, and that severe drought strongly decreased CDOM during the dry year. Large lakes, especially, with a presumed high degree of catchment uncoupling, showed low CDOM during the dry year. However, in disagreement with our hypothesis, climate, land cover, and morphometry all showed a stronger impact on lake CDOM in wet vs. dry years. Thus, drought systematically weakened the predictability of CDOM variations at the same time as CDOM was offset toward lower values. Our results show that drought not only has a direct effect on CDOM, but also acts indirectly by changing the spatial regulation of CDOM in boreal lakes.

The influence effect of regional carbon emission reduction under the perspective of fiscal decentralization: Government intervention or market mechanism?

AbstractBased on the perspective of fiscal decentralization, the study focuses on 30 provinces in China and employs various econometric models including the threshold model, spatial econometric model, mediation model, and regulation model. The research findings indicate that fiscal decentralization has a double‐threshold effect on government intervention, market mechanisms, and regional carbon emission reduction. Both government intervention and market mechanisms have inhibiting effects on carbon emission, with significant coefficients of GOVI and MARM at the 1% level. The cooperation between government intervention and the market mechanism effectively limits carbon emissions. Government intervention facilitates regional carbon emission reduction through the construction of new infrastructures and energy structure transformation, yielding a significant intermediary effect. The market mechanism is positively regulated through green finance and technology innovation to promote regional carbon emission reduction. Moreover, government intervention enables the market to achieve carbon emission reduction more effectively, especially in areas with a higher degree of government intervention. Continuous improvement and upgrading of regional and national carbon markets are essential to attain the carbon peak and carbon neutrality goals. Furthermore, attracting more participants to these markets for emission control subjects is necessary to enhance the effectiveness of government–market coordination.

Fine mapping and candidate gene analysis of qSRC3 controlling the silk color in maize (Zea mays L.).

Fine mapping of the maize QTL qSRC3, responsible for red silk, uncovered the candidate gene ZmMYB20, which encodes an R2R3-MYB transcription factor, has light-sensitive expression, and putatively regulates genes expression associated with anthocyanin biosynthesis. Colorless silk is a key characteristic contributing to the visual quality of fresh corn intended for market distribution. Nonetheless, the identification of Mendelian trait loci and associated genes that control silk color has been scarce. In this study, a F2 population arising from the hybridization of the single-segment substitution line qSRC3MT1 with red silk, carrying an introgressed allele from teosinte (Zea mays ssp. mexicana), and the recurrent maize inbred line Mo17, characterized by light green silk, was utilized for fine mapping. We found that the red silk trait is controlled by a semi-dominant genetic locus known as qSRC3, and its expression is susceptible to light-mediated inhibition. Moreover, qSRC3 explained 68.78% of the phenotypic variance and was delimited to a 133.2kb region, which includes three genes. Subsequent expression analyses revealed that ZmMYB20 (Zm00001d039700), which encodes an R2R3-MYB transcription factor, was the key candidate gene within qSRC3. Yeast one-hybrid and dual-luciferase reporter assays provided evidence that ZmMYB20 suppresses the expression of two crucial anthocyanin biosynthesis genes, namely ZmF3H and ZmUFGT, by directly binding to their respective promoter regions. Our findings underscore the significance of light-inhibited ZmMYB20 in orchestrating the spatial and temporal regulation of anthocyanin biosynthesis. These results advance the production of colorless silk in fresh corn, responding to the misconception that fresh corn with withered colored silk is not fresh and providing valuable genetic resources for the improvement of sweet and waxy maize.

A palmitoylation-depalmitoylation relay spatiotemporally controls GSDMD activation in pyroptosis.

Gasdermin D (GSDMD) is the executor of pyroptosis, which is important for host defence against pathogen infection. Following activation, caspase-mediated cleavage of GSDMD releases an amino-terminal fragment (GSDMD-NT), which oligomerizes and forms pores in the plasma membrane, leading to cell death and release of proinflammatory cytokines. The spatial and temporal regulation of this process in cells remains unclear. Here we identify GSDMD as a substrate for reversible S-palmitoylation on C192 during pyroptosis. The palmitoyl acyltransferase DHHC7 palmitoylates GSDMD to direct its cleavage by caspases. Subsequently, palmitoylation of GSDMD-NT promotes its translocation to the plasma membrane, where APT2 depalmitoylates GSDMD-NT to unmask the C192 residue and promote GSDMD-NT oligomerization. Perturbation of either palmitoylation or depalmitoylation suppresses pyroptosis, leading to increased survival of mice with lipopolysaccharide-induced lethal septic shock and increased sensitivity to bacterial infection. Our findings reveal a model through which a palmitoylation-depalmitoylation relay spatiotemporally controls GSDMD activation during pyroptosis.

Realizing Stable Perovskite Solar Cells with Efficiency Exceeding 25.6% Through Crystallization Kinetics and Spatial Orientation Regulation.

Organic-inorganic hybrid perovskites have emerged as highly promising candidates for photovoltaic applications, owing to the exceptional optoelectronic properties and low cost. Nonetheless, the performance and stability of solar cells suffer from the defect states of perovskite films aroused by non-optically active phases and non-centralized crystal orientation. Herein, a versatile organic molecule, Hydantoin, to modulate the crystallization of perovskite, is developed. Benefiting from the diverse functional groups, more spatially oriented perovskite films with high crystallinity are formed. This enhancement is accompanied by a conspicuous reduction in defect density, yielding efficiency of 25.66% (certified 25.15%), with superb environmental stability. Notably, under the standard measurement conditions (ISOS-L-1I), the maximum power point (MPP) output maintains 96.8% of the initial efficiency for 1600 h and exhibits excellent ion migration suppression. The synergistic regulation of crystallization and spatial orientation offers novel avenues for propelling perovskite solar cell (PSC) development.

Amber rainbow ribbon effect in broadband optical metamaterials

Using the trapped rainbow effect to slow down or even stop light has been widely studied. However, high loss and energy leakage severely limited the development of rainbow devices. Here, we observed the negative Goos-Hänchen effect in film samples across the entire visible spectrum. We also discovered an amber rainbow ribbon and an optical black hole due to perfect back reflection in optical waveguides, where little light leaks out. Not only does the amber rainbow ribbon effect show an automatic frequency selection response, as predicted by single frequency theoretical models and confirmed by experiments, it also shows spatial periodic regulation, resulting from broadband omnidirectional visible metamaterials prepared by disordered assembly systems. This broadband light trapping system could play a crucial role in the fields of optical storage and information processing when being used to construct ultra-compact modulators and other tunable devices.

Abstract 1686: Dissecting the 3D enhancer-promoter hubs in prostate tumorigenesis

Abstract The transcription process is controlled by regulatory elements that are often located in non-coding regions. Among regulatory elements, activities of enhancers that are bound by cell-type specific transcription factors (TFs) are tightly linked to cell identity. Enhancers loop to interact with the promoters of target genes at a distance to drive different cell fates. Evidently, transcriptional dysregulation linked to enhancers that are differentially activated in cancer is an underlying factor in tumorigenesis. To identify enhancers linked to prostate tumorigenesis, we analyzed hundreds of in-house and public H3K27ac ChIP-seq data generated from normal prostate and prostate cancer cell lines and tissues. We identified thousands of prostate cancer-specific enhancers (PSEs) that were activated exclusively in cancer conditions. To further identify the target genes of PSEs, we performed 3C-derived assays, such as Hi-C and Micro-C, and mapped genome-wide interactions. However, they were limited by the resolution to detect enhancer-promoter interactions. The recent development of Region Capture Micro-C (RCMC), a hybridization-based capture Micro-C method, allowed us to deeply map the highly nested interactions between regulatory elements. By utilizing RCMC, we generated high-resolution, focal contact maps that revealed comprehensive enhancer-promoter interactions near PSEs in prostate cancer cells. Interestingly, we found that PSEs loop to other PSEs clustered in the proximal genomic region, in addition to promoters of significantly upregulated genes in cancer compared to normal cells. We termed these regions as multi-connected "3D enhancer-promoter hubs”. To mechanistically dissect these hubs, we deleted 5+ PSEs one by one using the CRISPR/Cas9 system and performed multi-omics analyses, including RNA-seq and ChIP-seq. We found that single deletions of a subset of PSEs led to the downregulation of multiple genes looped to the deleted PSE as well as to other PSEs. Moreover, we found that deletion reduced the activity of other connected PSEs. When we further evaluated the chromatin contacts of regulatory elements in the PSE-deleted cells, we observed that many chromatin contacts remained unaffected. Finally, we identified TFs that bind to PSEs, and we are currently in the process of investigating enhancer-promoter hub connectivity by performing knockdown experiments on these TFs. Furthermore, we are using molecular assays to identify PSEs that could exert a phenotypic shift in cancer cell identity to drive prostate tumorigenesis. Overall, our study not only provides mechanistic insights into the spatial regulation of 3D enhancer-promoter hubs but also identifies new non-coding drivers in prostate tumorigenesis. Citation Format: Huan Cao, Zexun Wu, Leonardo Gonzalez-Smith, Seolyn Yang, Suhn K. Rhie. Dissecting the 3D enhancer-promoter hubs in prostate tumorigenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1686.

Disruptive, dangerous, and dirty: active travel measures as a ‘cause’ of car-related externalities

Automobility centred on private car use generates various externalities – or ‘antagonisms’ – that threaten its sustainability as a mobility regime. Through expanding the practice and spaces of driving, mass immobility can result. With increased car use, comes increased energy use, generating an ecological antagonism for this regime. Finally, greater car use has resulted in mass road traffic injuries and fatalities, which presents another threat to the growth and maintenance of this unique form of automobility. While these antagonisms present a risk, they have also been leveraged as a means to establish and secure the dominance of automobility. As part of a wider study exploring discourses of opposition to redistributive active travel measures in Dún Laoghaire-Rathdown, Ireland, this paper illustrates how active travel measures that present a challenge to automobility are depicted as disruptive, dangerous and dirty. These measures, precisely designed to mitigate the antagonisms of mass car use, are construed instead as primary causes of these systemic externalities. This study thereby reveals how active travel spaces themselves – and spatial regulations that favour active travellers – can be unfavourably represented as a means of politically sustaining automobility.

Mexican hospitality migrants and the spatial and geographic regulation of mobility

Mobility (and control over it) is partially mediated by migrant capital and how it is evaluated across time and space. This study draws on the concept of multiple migration – wherein migration is viewed as potentially multidirectional and open-ended over the life course – to examine the plight of male, Mexican hospitality staff globally on the move. These participants are unique in that they had experience working as hospitality staff in different countries under different legal classifications. In the US they were undocumented, in Mexico they were deported nationals, and in Canada they were received as temporary migrant workers. Their accounts bring different mobilities – illegal, forced, contract, and returned – under one analytical frame to illuminate how mobilities are spatially and geographically regulated. As the article details, their mobility depended on the resources they accrued during migration and whether these resources could be converted into relevant capital, with class, gender and race significant mediating factors. When contextualised, their accounts offer unique insights into immigration controls, transnational labour regimes, political economy and how access to capital shapes gendered identities and hierarchies. Their evaluations vis-à-vis other (global) workers also mediated their legal incorporation, governed by normative ideals that shape prospects and life outcomes in the current economy.

Enhancing the Output Performance of Triboelectric Nanogenerator Through Regulation of its Internal Nano-Architecture.

Triboelectric Nanogenerator (TENG) has proven highly effective in converting mechanical energy into electrical energy. Previous research on manipulating microstructure for performance enhancement primarily focused on the surface of TENGs. In this study, an innovative bottom-up strategic design to control the internal nano-architecture for the enhanced output of TENG is proposed. This multiscale structural design strategy consists of defect chemistry (angstrom-scale), surface modification (nano-scale), and spatial regulation of nanoparticles (meso-scale), which helps explore the optimal utilization of TENG's internal structure. After fine-tuning the nano-architecture, the output voltage is significantly increased. This optimized TENG serves as a robust platform for developing self-powered systems, including self-powered electrochemical chlorination systems for sterilization. Additionally, through the utilization of multiscale simulations (density functional theory, all-atom molecular dynamics, and dissipative particle dynamics), the underlying mechanisms governing how the optimized nanoparticle-polymer interface and spatial arrangement of nanoparticles influence the storage and transfer of charges are comprehensively elucidated. This study not only demonstrates the effectiveness of manipulating internal nano-architecture to enhance TENG performance for practical applications but also provides invaluable insights into structural engineering for TENG advancement.

AFM Imaging Reveals MicroRNA-132 to be a Positive Regulator of Synaptic Functions.

The modification of synaptic and neural connections in adults, including the formation and removal of synapses, depends on activity-dependent synaptic and structural plasticity. MicroRNAs (miRNAs) play crucial roles in regulating these changes by targeting specific genes and regulating their expression. The fact that somatic and dendritic activity in neurons often occurs asynchronously highlights the need for spatial and dynamic regulation of protein synthesis in specific milieu and cellular loci. MicroRNAs, which can show distinct patterns of enrichment, help to establish the localized distribution of plasticity-related proteins. The recent study using atomic force microscopy (AFM)-based nanoscale imaging reveals that the abundance of miRNA(miR)-134 is inversely correlated with the functional activity of dendritic spine structures. However, the miRNAs that are selectively upregulated in potentiated synapses, and which can thereby support prospective changes in synaptic efficacy, remain largely unknown. Using AFM force imaging, significant increases in miR-132 in the dendritic regions abutting functionally-active spines is discovered. This study provides evidence for miR-132 as a novel positive miRNA regulator residing in dendritic shafts, and also suggests that activity-dependent miRNAs localized in distinct sub-compartments of neurons play bi-directional roles in controlling synaptic transmission and synaptic plasticity.

Small-scale fisheries, large-scale fisheries and fisheries governance in the Philippines

ABSTRACT This article investigates the intersections between two highly significant ocean policy processes: fisheries governance interventions for improved sustainability, and the relationship between small- and large-scale fishers. The focus is on how fisheries governance interventions interact with longstanding tensions between small- and large-scale fishers. The article draws on three examples of contemporary policy debates about fisheries governance in the Philippines: measures against illegal, unreported and unregulated (IUU) fishing, closed seasons, and initiatives to re-organise spatial regulations governing fishing access. The article shows how in each case, debates about fisheries governance cannot be separated from the relationships between small and large scale fishers. Small- and large-scale fishers are affected differently by each governance intervention, and responses to this differentiation subsequently influence governance outcomes. The article finds that a key concern for any fisheries governance intervention needs to be assessing the relationships between key stakeholders, how these relationships will be modified by any governance intervention, and how these relational dynamics are likely to affect governance outcomes.

Land use data can improve the accuracy of carbon emission spatial inversion model

AbstractInvestigating the spatial distribution and correlation characteristics of carbon emissions would be conducive to the policy formulation for precise carbon emission spatial reduction. Firstly, a new carbon emission spatial inversion model was developed, incorporating nighttime light data and land use data. After verifying the validity and accuracy of the inversion results, the continuous carbon emission spatial data in the Beijing‐Tianjin‐Hebei Urban Agglomeration (BTHUA) were acquired from 2000 to 2019. Then, the spatial distribution and correlation characteristics were further analyzed in the BTHUA. Finally, policy recommendations were proposed for carbon emission reduction and urban sustainable development. The results showed that the built model can improve the accuracy of the carbon emission spatial inversion data. The carbon emissions were low in the northwest and high in the southeast of the BTHUA, with a noticeable expansion of the high carbon emission contiguous areas around Beijing, Tianjin, Shijiazhuang, and other prefecture‐level cities, which was consistent with the socioeconomic development pattern. The center of gravity of carbon emissions moved to the southeast, showing a relatively stable distribution. The spatial correlation degree of carbon emissions among cities gradually increased, with Beijing and Tianjin playing a prominent role. As a scientific tool, the spatial inversion model helps to produce more accurate spatial data. The results and conclusions can provide useful and scientific references for spatial analysis and regulation strategies of regional carbon emission reduction.

Nonlinear effects of dual-frequency focused ultrasound on the on-demand regulation of acoustic droplet vaporization

Dual-frequency ultrasound has been widely employed to enhance and regulate acoustic droplet vaporization (ADV) but the role of ultrasonic nonlinear effects on it remains unclear. The main objective of this study is to investigate the influence of nonlinear effects on the control of ADV nucleation under different dual-frequency focused ultrasound conditions. ADV nucleation of PFC nanodroplets activated by nonlinear dual-frequency ultrasound was modeled and parametric studies were conducted to investigate the influence of dual-frequency ultrasound frequency and acoustic power on the degree of nonlinearity (DoN), nucleation rates and dimensions of the nucleation region in a wide parameter range. The results showed that the ultrasonic nonlinearity caused a significant decrease in peak negative pressure due to waveform distortion, which leads to a lower nucleation rate in the nonlinear model compared to that in the linear model. Furthermore, the distributions of nucleation regions were also affected by the interaction between waves of different frequencies and cloud-like spatial distributions were produced, which could be modulated by the dual-frequency ultrasound parameters and have great potentials in the spatial regulation of the ADV and customized treatment protocols in clinical applications. In addition, represented by 1.5 MHz + 3 MHz, such a dual-frequency combination of fundamental and second harmonic could effectively enhance ultrasonic nonlinear effects with relatively lower peak negative pressure and higher DoN. Therefore, nonlinear effect of the dual-frequency ultrasound plays an important role in the ADV regulation, which should be considered in the numerical model and practical applications.

Spatial regulation of immunity: unmasking the secrets of abaxial immunity to powdery mildew.

This article comments on: Wu Y, Sexton WK, Zhang Q, Bloodgood D, Wu Y, Hooks C, Coker F, Vasquez A, Wei C-I, Xiao S. 2024. Leaf abaxial immunity to powdery mildew in Arabidopsis is conferred by multiple defense mechanisms. Journal of Experimental Botany 75, 1465-1478.

An auxin research odyssey: 1989-2023.

The phytohormone auxin is at times called the master regulator of plant processes and has been shown to be a central player in embryo development, the establishment of the polar axis, early aspects of seedling growth, as well as growth and organ formation during later stages of plant development. The Plant Cell has been key, since the inception of the journal, to developing an understanding of auxin biology. Auxin regulated plant growth control is accomplished by both changes in the levels of active hormones and the sensitivity of plant tissues to these concentration changes. In this historical review, we chart auxin research as it has progressed in key areas and highlighting the role The Plant Cell played in these scientific developments. We focus on understanding auxin-responsive genes, transcription factors, reporter constructs, perception and signal transduction processes. Auxin metabolism is discussed from the development of tryptophan auxotrophic mutants, the molecular biology of conjugate formation and hydrolysis, indole-3-butyric acid metabolism and transport, and key steps in indole-3-acetic acid biosynthesis, catabolism and transport. This progress leads to an expectation of a more comprehensive understanding of the systems biology of auxin and the spatial and temporal regulation of cellular growth and development.