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Transcriptional reprogramming plays a key role in a variety of biological processes. Recent advances in RNA imaging techniques have allowed to visualize, in vivo, transcription-related mechanisms in different organisms. The MS2 system constitutes a robust method that has been used for over two decades to image multiple steps of a transcript's life cycle from "birth to death" with high spatiotemporal resolution in the animal field. It is based on the high affinity binding of the MS2 bacteriophage coat protein to its RNA hairpin ligands. Despite its broad applicability, a limited number of studies have implemented the system in plants, but without exploiting its full potential. Here, we describe the transposition of the MS2 technique to Arabidopsis. Combined with microfluidics, it allows to visualize the transcriptional repression of a phosphate starvation induced gene (SPX1) upon phosphate refeeding in vivo. The system provided access to the transcriptional response kinetics of individual cells, gene expression heterogeneity, and revealed bursting phenomena in plantae. The described methods provide new insights for multiple applications., (© 2025. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Hydathodes are small organs found on the leaf margins of vascular plants which release excess xylem sap through a process called guttation. While previous studies have hinted at additional functions of hydathode in metabolite transport or auxin metabolism, experimental support is limited. We conducted comprehensive transcriptomic, metabolomic and physiological analyses of mature Arabidopsis hydathodes. This study identified 1460 genes differentially expressed in hydathodes compared to leaf blades, indicating higher expression of most genes associated with auxin metabolism, metabolite transport, stress response, DNA, RNA or microRNA processes, plant cell wall dynamics and wax metabolism. Notably, we observed differential expression of genes encoding auxin-related transcriptional regulators, biosynthetic processes, transport and vacuolar storage supported by the measured accumulation of free and conjugated auxin in hydathodes. We also showed that 78% of the total content of 52 xylem metabolites was removed from guttation fluid at hydathodes. We demonstrate that NRT2.1 and PHT1;4 transporters capture nitrate and inorganic phosphate in guttation fluid, respectively, thus limiting the loss of nutrients during this process. Our transcriptomic and metabolomic analyses unveil an organ with its specific physiological and biological identity., (© 2024 Society for Experimental Biology and John Wiley & Sons Ltd.)

Adapting to varying phosphate levels in the environment is vital for plant growth. The PHR1 phosphate starvation response transcription factor family, along with SPX inhibitors, plays a pivotal role in plant phosphate responses. However, this regulatory hub intricately links with diverse biotic and abiotic signaling pathways, as outlined in this review. Understanding these intricate networks is crucial, not only on a fundamental level but also for practical applications, such as enhancing sustainable agriculture and optimizing fertilizer efficiency. This comprehensive review explores the multifaceted connections between phosphate homeostasis and environmental stressors, including various biotic factors, such as symbiotic mycorrhizal associations and beneficial root-colonizing fungi. The complex coordination between phosphate starvation responses and the immune system are explored, and the relationship between phosphate and nitrate regulation in agriculture are discussed. Overall, this review highlights the complex interactions governing phosphate homeostasis in plants, emphasizing its importance for sustainable agriculture and nutrient management to contribute to environmental conservation., (© 2024. The Author(s) under exclusive licence to The Botanical Society of Japan.)

Efficiently regulating growth to adapt to varying resource availability is crucial for organisms, including plants. In particular, the acquisition of essential nutrients is vital for plant development, as a shortage of just one nutrient can significantly decrease crop yield. However, plants constantly experience fluctuations in the presence of multiple essential mineral nutrients, leading to combined nutrient stress conditions. Unfortunately, our understanding of how plants perceive and respond to these multiple stresses remains limited. Unlocking this mystery could provide valuable insights and help enhance plant nutrition strategies. This review focuses specifically on the regulation of phosphorous homeostasis in plants, with a primary emphasis on recent studies that have shed light on the intricate interactions between phosphorous and other essential elements, such as nitrogen, iron, and zinc, as well as non-essential elements like aluminum and sodium. By summarizing and consolidating these findings, this review aims to contribute to a better understanding of how plants respond to and cope with combined nutrient stress., (© 2023 Society for Experimental Biology and John Wiley & Sons Ltd.)

Intracellular inorganic orthophosphate (Pi) distribution and homeostasis profoundly affect plant growth and development. However, its distribution patterns remain elusive owing to the lack of efficient cellular Pi imaging methods. Here we develop a rapid colorimetric Pi imaging method, inorganic orthophosphate staining assay (IOSA), that can semi-quantitatively image intracellular Pi with high resolution. We used IOSA to reveal the alteration of cellular Pi distribution caused by Pi starvation or mutations that alter Pi homeostasis in two model plants, rice and Arabidopsis, and found that xylem parenchyma cells and basal node sieve tube element cells play a critical role in Pi homeostasis in rice. We also used IOSA to screen for mutants altered in cellular Pi homeostasis. From this, we have identified a novel cellular Pi distribution regulator, HPA1/PHO1;1, specifically expressed in the companion and xylem parenchyma cells regulating phloem Pi translocation from the leaf tip to the leaf base in rice. Taken together, IOSA provides a powerful method for visualizing cellular Pi distribution and facilitates the analysis of Pi signalling and homeostasis from the level of the cell to the whole plant., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

Single-molecule fluorescence in situ hybridization (smFISH) is a powerful method for the visualization and quantification of individual RNA molecules within intact cells. With its ability to probe gene expression at the single cell and single-molecule level, the technique offers valuable insights into cellular processes and cell-to-cell heterogeneity. Although widely used in the animal field, its use in plants has been limited. Here, we present an experimental smFISH workflow that allows researchers to overcome hybridization and imaging challenges in plants, including sample preparation, probe hybridization, and signal detection. Overall, this protocol holds great promise for unraveling the intricacies of gene expression regulation and RNA dynamics at the single-molecule level in whole plants., (© 2024. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Potassium (K + ) is an essential macronutrient for plant growth. The transcriptional regulation of K + transporter genes is one of the key mechanisms by which plants respond to K + deficiency. Among the HAK/KUP/KT transporter family, HAK5, a high-affinity K + transporter, is essential for root K + uptake under low external K + conditions. HAK5 expression in the root is highly induced by low external K + concentration. While the molecular mechanisms of HAK5 regulation have been extensively studied, it remains unclear how plants sense and coordinates K + uptake and translocation in response to changing environmental conditions. Using skor mutants, which have a defect in root-to-shoot K + translocation, we have been able to determine how the internal K + status affects the expression of HAK5 . In skor mutant roots, under K + deficiency, HAK5 expression was lower than in wild-type although the K + concentration in roots was not significantly different. These results reveal that HAK5 is not only regulated by external K + conditions but it is also regulated by internal K + levels, which is in agreement with recent findings. Additionally, HAK5 plays a major role in the uptake of Cs + in roots. Therefore, studying Cs + in roots and having more detailed information about its uptake and translocation in the plant would be valuable. Radioactive tracing experiments revealed not only a reduction in the uptake of 137 Cs + and 42 K + in skor mutants compared to wild-type but also a different distribution of 137 Cs + and 42 K + in tissues. In order to gain insight into the translocation, accumulation, and repartitioning of both K + and Cs + in plants, long-term treatment and split root experiments were conducted with the stable isotopes 133 Cs + and 85 Rb + . Finally, our findings show that the K + distribution in plant tissues regulates root uptake of K + and Cs + similarly, depending on HAK5 ; however, the translocation and accumulation of the two elements are different., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Kanno, Martin, Vallier, Chiarenza, Nobori, Furukawa, Nussaume, Vavasseur and Leonhardt.)

Background: Inorganic phosphate (Pi) is the sole source of phosphorus for plants. It is a limiting factor for plant yield in most soils worldwide. Due to economic and environmental constraints, the use of Pi fertilizer is and will be more and more limited. Unfortunately, evaluation of Pi bioavailability or Pi starvation traits remains a tedious task, which often does not inform us about the real Pi plant status., Results: Here, we identified by transcriptomic studies carried out in the plant model Arabidopsis thaliana, early roots- or leaves-conserved molecular markers for Pi starvation, exhibiting fast response to modifications of phosphate nutritional status. We identified their homologues in three crops (wheat, rapeseed, and maize) and demonstrated that they offer a reliable opportunity to monitor the actual plant internal Pi status. They turn out to be very sensitive in the concentration range of 0-50 µM which is the most common case in the vast majority of soils and situations where Pi hardly accumulates in plants. Besides in vitro conditions, they could also be validated for plants growing in the greenhouse or in open field conditions., Conclusion: These markers provide valuable physiological tools for plant physiologists and breeders to assess phosphate bio-availability impact on plant growth in their studies. This also offers the opportunity to cope with the rising economical (shortage) and societal problems (pollution) resulting from the management of this critical natural resource., (© 2023. BioMed Central Ltd., part of Springer Nature.)

Phosphate (Pi) is involved in numerous metabolic processes and plays a vital role in plant growth. Green plants have evolved intricate molecular bases of Pi signaling to maintain cellular Pi homeostasis. Here, we summarize recent advances in the molecular and structural bases of central Pi signaling and discuss pending questions., Competing Interests: Declaration of interests No interests are declared., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The coordinated distribution of inorganic phosphate (Pi) between roots and shoots is an important process that plants use to maintain Pi homeostasis. SHORT-ROOT (SHR) is well characterized for its function in root radial patterning. Here we demonstrate a role of SHR in controlling Pi allocation from root to shoot by regulating PHOSPHATE1 in the root differentiation zone. We recovered a weak mutant allele of SHR in Arabidopsis that accumulates much less Pi in the shoot and shows a constitutive Pi starvation response under Pi-sufficient conditions. In addition, Pi starvation suppresses SHR protein accumulation and releases its inhibition on the HD-ZIP III transcription factor PHB. PHB accumulates and directly binds the promoter of PHOSPHATE2 to upregulate its transcription, resulting in PHOSPHATE1 degradation in the xylem-pole pericycle cells. Our findings reveal a previously unrecognized mechanism of how plants regulate Pi translocation from roots to shoots., (© 2022. The Author(s), under exclusive licence to Springer Nature Limited.)

Aluminum (Al) is a major limiting factor for crop production on acidic soils, inhibiting root growth and plant development. At acidic pH (pH < 5.5), Al 3+ ions are the main form of Al present in the media. Al 3+ ions have an increased solubility at pH < 5.5 and result in plant toxicity. At higher pH, the free Al 3+ fraction decreases in the media, but whether plants can detect Al at these pHs remain unknown. To cope with Al stress, the SENSITIVE TO PROTON RHIZOTOXICITY1 (STOP1) transcription factor induces AL-ACTIVATED MALATE TRANSPORTER1 ( ALMT1 ), a malate-exuding transporter as a strategy to chelate the toxic ions in the rhizosphere. Here, we uncoupled the Al signalling pathway that controls STOP1 from Al toxicity using wild type (WT) and two stop1 mutants carrying the pALMT1:GUS construct with an agar powder naturally containing low amounts of phosphate, iron (Fe), and Al. We combined gene expression [real-time PCR (RT-PCR) and the pALMT1:GUS reporter], confocal microscopy ( pSTOP1:GFP-STOP1 reporter), and root growth measurement to assess the effects of Al and Fe on the STOP1-ALMT1 pathway in roots. Our results show that Al triggers STOP1 signaling at a concentration as little as 2 μM and can be detected at a pH above 6.0. We observed that at pH 5.7, 20 μM AlCl 3 induces ALMT1 in WT but does not inhibit root growth in stop1 Al-hypersensitive mutants. Increasing AlCl 3 concentration (>50 μM) at pH 5.7 results in the inhibition of the stop1 mutants primary root. Using the green fluorescent protein (GFP)-STOP1 and ALMT1 reporters, we show that the Al signal pathway can be uncoupled from the Al toxicity on the root. Furthermore, we observe that Al strengthens the Fe-mediated inhibition of primary root growth in WT, suggesting an interaction between Fe and Al on the STOP1-ALMT1 pathway., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Le Poder, Mercier, Février, Duong, David, Pluchon, Nussaume and Desnos.)

Photosynthetic organisms convert light energy into chemical energy stored in carbohydrates. To perform this process, an adequate supply of essential mineral elements, such as iron, is required in the chloroplast. Because iron plays a crucial role during electron transport and chlorophyll formation, iron deficiency alters photosynthesis and promotes chlorosis, or the yellowing of leaves. Intriguingly, iron deficiency-induced chlorosis can be reverted by the depletion of other micronutrients [i.e., manganese (Mn)] or macronutrients [i.e., sulfur (S) or phosphorus (P)], raising the question of how plants integrate nutrient status to control photosynthesis. Here, we review how improving our understanding of the complex relationship between nutrient homeostasis and photosynthesis has great potential for crop improvement., Competing Interests: Declaration of interests None are declared., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Soil availability of inorganic ortho-phosphate (PO 4 3- , P i ) is a key determinant of plant growth and fitness. 1 Plants regulate the capacity of their roots to take up inorganic phosphate by adapting the abundance of H + -coupled phosphate transporters of the PHOSPHATE TRANSPORTER 1 (PHT1) family 2 at the plasma membrane (PM) through transcriptional and post-translational changes driven by the genetic network of the phosphate starvation response (PSR). 3-8 Increasing evidence also shows that plants integrate immune responses to alleviate phosphate starvation stress through the association with beneficial microbes. 9-11 Whether and how such phosphate transport is regulated upon activation of immune responses is yet uncharacterized. To address this question, we first developed quantitative assays based on changes in the electrical PM potential to measure active P i transport in roots in real time. By inserting micro-electrodes into bulging root hairs, we were able to determine key characteristics of phosphate transport in intact Arabidopsis thaliana (hereafter Arabidopsis) seedlings. The fast P i -induced depolarization observed was dependent on the activity of the major phosphate transporter PHT1;4. Notably, we observed that this PHT1;4-mediated phosphate uptake is repressed upon activation of pattern-triggered immunity. This inhibition depended on the receptor-like cytoplasmic kinases BOTRYTIS-INDUCED KINASE 1 (BIK1) and PBS1-LIKE KINASE 1 (PBL1), which both phosphorylated PHT1;4. As a corollary to this negative regulation of phosphate transport by immune signaling, we found that PHT1;4-mediated phosphate uptake normally negatively regulates anti-bacterial immunity in roots. Collectively, our results reveal a mechanism linking plant immunity and phosphate homeostasis, with BIK1/PBL1 providing a molecular integration point between these two important pathways., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 The Author(s). Published by Elsevier Inc. All rights reserved.)