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Most ferns, unlike all seed plants, are homosporous and produce sexually undifferentiated spores. Sex ratio in many homosporous species is environmentally established by the secretion of antheridiogen from female/hermaphrodite gametophytes. Nearby undetermined gametophytes perceive antheridiogen, which induces male development. In the fern Ceratopteris richardii (Ceratopteris), hermaphroditic (her) mutants develop as hermaphrodites even in the presence of antheridiogen. Modern sequencing and genomic tools make the molecular identification of mutants in the 11-Gbp genome of this fern possible. We mapped 2 linked mutants, her7-14 and her7-19, to the same 16-Mbp interval on chromosome 29 of the Ceratopteris genome. An ortholog of the receptor kinase gene BRASSINOSTEROID INSENSITIVE 1 (BRI1) within this interval encoded a deletion mutation in her7-14 and a missense mutation in her7-19. Three other linked her mutants encoded missense mutations in the same gene, which we name HER7. Consistent with a function as a receptor kinase, HER7-GFP fusion protein localized to the plasma membrane and cytoplasm. Analysis of gene expression showed that brassinosteroid biosynthesis was upregulated in hermaphrodites compared with male gametophytes. Our work demonstrates that HER7 is required for sex determination in Ceratopteris and opens avenues for studying the evolution of antheridiogen systems. 

Land plants alternate between asexual sporophytes and sexual gametophytes. Unlike seed plants, ferns develop free-living gametophytes. Gametophytes of the model fern Ceratopteris exhibit two sex types: hermaphrodites with pluripotent meristems and males lacking meristems. In the absence of the pheromone antheridiogen, males convert to hermaphrodites by forming de novo meristems, although the mechanisms remain unclear. Using long-term time-lapse imaging and computational analyses, we captured male-to-hermaphrodite conversion at single-cell resolution and reconstructed the lineage and division atlas of newly formed meristems. Lineage tracing revealed that the de novo-formed meristem originates from a single non-antheridium cell: the meristem progenitor cell (MPC). During conversion, the MPC lineage showed increased mitotic activity, with marginal cells proliferating faster than inner cells. A mathematical model suggested that stochastic variation in cell division, combined with strong inhibitory signals from dividing marginal cells, is sufficient to explain gametophyte dynamics. Experimental disruption of division timing agreed with the model, showing that precise cell cycle progression is essential for MPC establishment and sex-type conversion. These findings reveal cellular mechanisms governing sex conversion and de novo meristem formation in land plants. 

Accurate prediction of citywide crowd activity levels (CALs),i.e., the numbers of participants of citywide crowd activities under different venue categories at certain time and locations, is essential for the city management, the personal service applications, and the entrepreneurs in commercial strategic planning. Existing studies have not thoroughly taken into account the complex spatial and temporal interactions among different categories of CALs and their extreme occurrences, leading to lowered adaptivity and accuracy of their models. To address above concerns, we have proposedIE-CALP, a novel spatio-temporalInteractive attention-based andExtreme-aware model forCrowdActivityLevelPrediction. The tasks ofIE-CALPconsist of(a)forecasting the spatial distributions of various CALs at different city regions (spatial CALs), and(b)predicting the number of participants per category of the CALs (categorical CALs). To realize above, we have designed a novel spatial CAL-POI interaction-attentive learning component inIE-CALPto model the spatial interactions across different CAL categories, as well as those among the spatial urban regions and CALs. In addition,IE-CALPincorporate the multi-level trends (e.g., daily and weekly levels of temporal granularity) of CALs through a multi-level temporal feature learning component. Furthermore, to enhance the model adaptivity to extreme CALs (e.g., during extreme urban events or weather conditions), we further take into account theextreme value theoryand model the impacts of historical CALs upon the occurrences of extreme CALs. Extensive experiments upon a total of 738,715 CAL records and 246,660 POIs in New York City (NYC), Los Angeles (LA), and Tokyo have further validated the accuracy, adaptivity, and effectiveness ofIE-CALP’s interaction-attentive and extreme-aware CAL predictions. 

Most land plants alternate between generations of sexual gametophytes and asexual sporophytes. Unlike seed plants, fern gametophytes are free-living and grow independently of their sporophytes. In homosporous ferns like Ceratopteris, gametophytes derived from genetically identical spores exhibit sexual dimorphism, developing as either males or hermaphrodites. Males lack meristems and promote cell differentiation into sperm-producing antheridia. In contrast, hermaphrodites initiate multicellular meristems that stay undifferentiated, sustain cell division and prothallus expansion, and drive the formation of egg-producing archegonia. Once initiating the meristem, hermaphrodites secrete the pheromone antheridiogen, which triggers neighboring slower-growing gametophytes to develop as males, while the hermaphrodites themselves remain insensitive to antheridiogen. This strategy promotes outcrossing and prevents all individuals in the colony from becoming males. This study reveals that an evolutionarily conserved GRAS domain transcriptional regulator (CrHAM), directly repressed by Ceratopteris microRNA171 (CrmiR171), promotes meristem development in Ceratopteris gametophytes and determines the male-to-hermaphrodite ratio in the colony. CrHAM preferentially accumulates within the meristems of hermaphrodites but is excluded from differentiated antheridia. CrHAM sustains meristem proliferation and cell division through conserved hormone pathways. In the meantime, CrHAM inhibits the antheridiogen-induced conversion of hermaphrodites to males by suppressing the male program expression and preventing meristem cells from differentiating into sperm-producing antheridia. This finding establishes a connection between meristem indeterminacy and sex determination in ferns, suggesting both conserved and diversified roles of meristem regulators in land plants. 

Accurate citywide crowd activity prediction (CAP) can enable proactive crowd mobility management and timely responses to urban events, which has become increasingly important for a myriad of smart city planning and management purposes. However, complex correlations across the crowd activities, spatial and temporal urban environment features and theirinteractivedependencies, and relevant external factors (e.g., weather conditions) make it highly challenging to predict crowd activities accurately in terms of different venue categories (for instance, venues related to dining, services, and residence) and varying degrees (e.g., daytime and nighttime). To address the above concerns, we proposeSTICAP, a citywide spatio-temporal interactive crowd activity prediction approach. In particular,STICAPtakes in the location-based social network check-in data (e.g., from Foursquare/Gowalla) as the model inputs and forecasts the crowd activity within each time step for each venue category. Furthermore, we have integrated multiple levels of temporal discretization to interactively capture the relations with historical data. Then, three parallelResidual Spatial Attention Networks(RSAN) in theSpatial Attention Componentexploit the hourly, daily, and weekly spatial features of crowd activities, which are further fused and processed by theTemporal Attention Componentforinteractive CAP. Along with other external factors such as weather conditions and holidays,STICAPadaptively and accurately forecasts the final crowd activities per venue category, enabling potential activity recommendation and other smart city applications. Extensive experimental studies based on three different real-world crowd activity datasets have demonstrated that our proposedSTICAPoutperforms the baseline and state-of-the-art algorithms in CAP accuracy, with an average error reduction of 35.02%. 

Solar-induced chlorophyll fluorescence (SIF) is widely accepted as a proxy for gross primary productivity (GPP). Among the various SIF measurements, tower-based SIF measurements allow for continuous monitoring of SIF variation at a canopy scale with high temporal resolution, making it suitable for monitoring highly variable plant physiological responses to environmental changes. However, because of the strong and close relationship between SIF and absorbed photosynthetically active radiation (aPAR), it may be difficult to detect the influence of environmental drivers other than light conditions. Among the drivers, atmospheric dryness (vapor pressure deficit, VPD) is projected to increase as drought becomes more frequent and severe in the future, negatively impacting plants. In this study, we evaluated the tower-based high-frequency SIF measurement as a tool for detecting plant response to highly variable VPD. The study was performed in a mixed temperate forest in Virginia, USA, where a 40-m-tall flux tower has been measuring gas and energy exchanges and ancillary environmental drivers, and the Fluospec 2 system has been measuring SIF. We show that a proper definition of light availability to vegetation can reproduce SIF response to changing VPD that is comparable to GPP response as estimated from eddy covariance measurement: GPP decreased with rising VPD regardless of how aPAR was defined, whereas SIF decreased only when aPAR was defined as the PAR absorbed by chlorophyll (aPARchl) or simulated by a model (Soil Canopy Observation, Photochemistry and Energy fluxes, SCOPE). We simulated the effect of VPD on SIF with two different simulation modes of fluorescence emission representing contrasting moisture conditions, ‘Moderate’ and ‘Soil Moisture (SM) Stress’ modes. The decreasing SIF to rising VPD was only found in the SM Stress mode, implying that the SIF-VPD relationship depends on soil moisture conditions. Furthermore, we observed a similar response of SIF to VPD at hourly and daily scales, indicating that satellite measurements can be used to study the effects of environmental drivers other than light conditions. Finally, the definition of aPAR emphasizes the importance of canopy structure research to interpret remote sensing observations properly.