Sulfur (S) is an essential macronutrient for plants and its availability in soils is a relevant determinant for plant growth and development. Current regulatory policies aimed at reducing industrial S emissions and changes in agronomical practices have caused a decline in S contents in soils worldwide. Deficiency of sulfate — the primary form of S accessible to plants in soil — has adverse effects on both crop yield and nutritional quality. Therefore, recent research has increasingly focused on unraveling the molecular mechanisms through which plants detect and adapt to a limiting supply of sulfate. A significant part of these studies involves the use of omics technologies and has generated comprehensive catalogs of sulfate deficiency-responsive genes and processes, principally in Arabidopsis thaliana, with a few studies centering on crop species such as wheat, rice or members of the Brassica genus. Although we know that sulfate deficiency elicits an important reprogramming of the transcriptome, the transcriptional regulators orchestrating this response are not yet well understood. In this review, we summarize the knowledge on gene expression responses to sulfate deficiency and current efforts on the identification of transcription factors relevant for controlling this response. We further compare the transcriptional response and putative regulators between Arabidopsis thaliana and two relevant crop plants, rice and tomato, to gain insights into common mechanisms of response to sulfate deficiency.

The increasing availability of omics data from non-model plant species has created a pressing need for centralized, user-friendly platforms that maximize the utility of these datasets in a FAIR manner. Here, we introduce PlantaeViz, a web-based tool designed for the integration, visualization, and analysis of multi-omics data across a wide range of plant species. PlantaeViz offers advanced functionalities, including gene catalogues built from curated literature, transcriptomic meta-analyses presented as gene expression atlases, gene co-expression and regulatory networks with on-the-fly ontology analyses, cistrome visualization and metabolomics-transcriptomics integration, among other tools, providing a robust framework for hypothesis generation and biological interpretation. Gene Cards applications, tailored to each plant species, provide both community-curated and automatically generated functional annotation information. One of the platform's core features is its big data approach: over 58,000 publicly available SRA transcriptomic samples have been processed and visualized to date. Significant efforts have been made in orthology assessment using multiple layers of evidence, as well as in the automatic classification and standardization of omics metadata through regular expressions and data mining. As a result, around 90% of transcriptomic runs have been successfully classified according to sample tissue. These data have been used to construct gene networks via computationally intensive methods based on diverse algorithms. We present a study case to illustrate the platform's integration and exploratory capabilities. PlantaeViz bridges genomics and functional knowledge between model and non-model plant species and aims to expand its species catalogue of species in the future, democratizing access to large-scale plant omics data. Further developments will include the incorporation of additional data types, and the implementation of new tools to further support plant research across diverse biological contexts.

Sulfate availability critically influences plant growth, yet the role of small RNAs, particularly microRNAs (miRNAs), in regulating responses to sulfate deficiency remains poorly understood. Here, we conducted a temporal analysis of sulfate deficiency-responsive miRNAs in the roots and leaves of Solanum lycopersicum (tomato), using an updated miRNA annotation in the SL4.0 genome. We found 40 differentially expressed miRNAs, including 2 novel, tomato-specific miRNAs. Tomato miRNAs showed an important time- and organ-specific regulation, similar to the described response of the mRNA transcriptome. Integration with transcriptomic data and Degradome-seq analysis highlighted both canonical and non-canonical targets for sulfate-responsive miRNAs. miR395, the most extensively studied miRNA, was found to control not only its conserved targets involved in sulfate transport and assimilation, but also genes involved in redox homeostasis, photosynthesis and chloride transport. Notably, most targets were repressed in leaves, suggesting miRNA-mediated downregulation of energy-intensive processes, while root targets were predominantly upregulated, including genes related to protein remodeling and antioxidant defense. Comparative analysis with Arabidopsis thaliana revealed a broader functional repertoire in tomato, suggesting species-specific adaptations to sulfate deficiency. Overall, our results underscore the critical role of miRNAs in fine-tuning organ-specific metabolic reprogramming during nutrient stress, expanding the current understanding of the regulatory landscape underlying sulfate deficiency in plants.

Mutualistic interactions between plants and beneficial fungi rely on extensive transcriptional reprogramming in both partners, yet the underlying regulatory mechanisms coordinating these responses remain incompletely understood. Here, we combined a transcriptomics analysis with a gene regulatory network (GRN) inference to dissect the interaction between Arabidopsis thaliana and the growth-promoting fungus Trichoderma atroviride. At an early but established stage of colonization (72 h post-inoculation), we identified widespread transcriptional changes in both of the organisms, including host activation of hypoxia, stress and root development-related pathways in Arabidopsis, and fungal reprogramming of membrane transport and primary metabolism. Using DNA-binding motifs and GENIE3-based regulatory inference, we reconstructed interaction-specific GRNs for each species. The subnetworks focused on the main differentially expressed biological processes and uncovered ERF-, WRKY-, NAC- and DOF-centered modules linking hypoxia responses with developmental remodeling in the plant, whereas the putative orthologs of TFs involved in developmental and stress-related TFs in fungi, such as CrzA, RME1, NsdC, PacC and RPN4, formed a regulatory core coordinating fungal transport and metabolic adjustment. In parallel, we uncovered contrasting sRNA dynamics between the partners. While the Arabidopsis sRNA changes were limited, T. atroviride exhibited a strong induction of 20–22 nt sRNAs, including a small set of high-confidence sRNA–mRNA interactions targeting host genes involved in root function and immunity. Together, our results extend previous pathway-based descriptions of the Arabidopsis–Trichoderma mutualism and provide a systems-level, testable framework for how coordinated regulatory programs in both of the partners support the interaction.

Sulfur is an essential element for biological molecules, with sulfate as the primary sulfur source for plants. Under sulfate-deficiency, plants undergo physiological, metabolic, transcriptional, and post-transcriptional changes. Although Solanum lycopersicum (tomato) exhibits extensive transcriptome reprogramming during sulfate deficiency, the role of microRNAs (miRNAs) in this response remains poorly explored. In this study, we analyzed miRNAs expression in tomato roots and leaves at 3- and 4-weeks post-sowing under sulfate-sufficient and sulfate-deficient conditions, leveraging a de novo annotation of miRNA genes in the SL4.0 genome. We identified several miRNAs showing tissue- and time-specific expression changes in response to sulfate deficiency, with a potential role in processes such as lignin, chlorophyll, and polysaccharides metabolism. Consistent with other plants, miR395 emerged as a key sulfur metabolism and transport regulator. Notably, we identified a novel miR395 target, SlERF2a, an Ethylene-Responsive Factor predicted to regulate numerous sulfate deficiency-responsive genes, including genes involved in plastid organization, detoxification, sulfur assimilation and starvation response. These results suggest a broader role for miR395 in sulfate-deficiency responses in tomato compared to other plants. This work provides new insights into the post-transcriptional regulation of sulfate-deficiency in tomato, providing an updated miRNA annotation for future studies on miRNA-mediated regulation in this relevant crop.

Tomato ( Solanum lycopersicum ) is a globally important crop, yet the gene regulatory networks (GRNs) controlling gene expression remain poorly understood. In this study, we constructed GRNs for roots, leaves, flowers, fruits, and seeds by inferring transcription factor (TF)–target interactions from over 10,000 RNA-seq libraries using the GENIE3 algorithm. We refined these networks with gene co-expression data and computational predictions of TF binding sequences in open chromatin sites. Our networks confirmed key TFs, including TOMATO AGAMOUS LIKE 1 and RIPENING INHIBITOR in fruit ripening, as well as ABF3 and ABF5 in abscisic acid response in leaves. Additionally, we identified novel candidate regulators, including AUXIN RESPONSE FACTOR 2A and ETHYLENE RESPONSE FACTOR.E2 in fruit ripening and G-BOX BINDING FACTOR 3 ( Sl GBF3) in ABA-related and drought pathways. To further validate the GRNs, we used DNA Affinity Purification Sequencing (DAP-seq) for Sl GBF3, confirming the accuracy of our GRNs. This study provides a valuable resource for dissecting transcriptional regulation in tomato, with potential applications in crop improvement. The GRNs are publicly accessible through a user-friendly web platform at https://plantaeviz.tomsbiolab.com/tomviz . Highlight: We developed organ-level gene regulatory networks for tomato using 10,000+ RNA-seq libraries, validated predictions and identified new regulators of fruit ripening and ABA response. These networks are available at https://plantaeviz.tomsbiolab.com/tomviz .