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Group VII ethylene-responsive factor (ERFVII) transcription factors are crucial for the adaption of plants to conditions that limit oxygen availability. A recent study by Zubrycka et al. reveals new aspects of ERFVII stabilization through the PLANT CYSTEINE OXIDASE (PCO)-N degron pathway and non-autonomous regulation in response to different endogenous and exogenous cues., Competing Interests: Declaration of interests None declared by authors., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Sulfur (S) is an essential mineral nutrient for plant growth and development; it is important for primary and specialized plant metabolites that are crucial for biotic and abiotic interactions. Foliar S content varies up to 6-fold under a controlled environment, suggesting an adaptive value under certain natural environmental conditions. However, a major quantitative regulator of S content in Arabidopsis thaliana has not been identified yet, pointing to the existence of either additional genetic factors controlling sulfate/S content or of many minor quantitative regulators. Here, we use overlapping information of two separate ionomics studies to select groups of accessions with low, mid, and high foliar S content. We quantify series of metabolites, including anions (sulfate, phosphate, and nitrate), thiols (cysteine and glutathione), and seven glucosinolates, gene expression of 20 genes, sulfate uptake, and three biotic traits. Our results suggest that S content is tightly connected with sulfate uptake, the concentration of sulfate and phosphate anions, and glucosinolate and glutathione synthesis. Additionally, our results indicate that the growth of pathogenic bacteria is enhanced in the A. thaliana accessions containing higher S in their leaves, suggesting a complex regulation between S homeostasis, primary and secondary metabolism, and biotic pressures., (© The Author(s) 2023. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

How different intrinsic sequence variations and regulatory modifications of histones combine in nucleosomes remain unclear. To test the importance of histone variants in the organization of chromatin we investigated how histone variants and histone modifications assemble in the Arabidopsis thaliana genome. We showed that a limited number of chromatin states divide euchromatin and heterochromatin into several subdomains. We found that histone variants are as significant as histone modifications in determining the composition of chromatin states. Particularly strong associations were observed between H2A variants and specific combinations of histone modifications. To study the role of H2A variants in organizing chromatin states we determined the role of the chromatin remodeler DECREASED IN DNA METHYLATION (DDM1) in the organization of chromatin states. We showed that the loss of DDM1 prevented the exchange of the histone variant H2A.Z to H2A.W in constitutive heterochromatin, resulting in significant effects on the definition and distribution of chromatin states in and outside of constitutive heterochromatin. We thus propose that dynamic exchanges of histone variants control the organization of histone modifications into chromatin states, acting as molecular landmarks., Competing Interests: BJ, ZL, EA, AO, VS, RY, SA, AK, FB No competing interests declared, (© 2023, Jamge, Lorković, Axelsson et al.)

Land plants have developed robust roots to grow in diverse soil ecosystems. The distal end of the root tip has a specialized organ called the 'root cap'. The root cap assists the roots in penetrating the ground, absorbing water and minerals, avoiding heavy metals and regulating the rhizosphere microbiota. Furthermore, root-cap-derived auxin governs the lateral root patterning and directs root growth under varying soil conditions. The root cap formation is hypothesized as one of the key innovations during root evolution. Morphologically diversified root caps in early land plant lineage and later in angiosperms aid in improving the adaptation of roots and, thereby, plants in diverse soil environments. This review article presents a retrospective view of the root cap's important morphological and physiological characteristics for the root-soil interaction and their response toward various abiotic and biotic stimuli. Recent single-cell RNAseq data shed light on root cap cell-type-enriched genes. We compiled root cap cell-type-enriched genes from Arabidopsis, rice, maize and tomato and analyzed their transcription factor (TF) binding site enrichment. Further, the putative gene regulatory networks derived from root-cap-enriched genes and their TF regulators highlight the species-specific biological functions of root cap genes across the four plant species., (© The Author(s) 2022. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Plant cells coated with hydrophobic compounds constitute a protective barrier to control movement of materials through plant tissues. In roots, the endodermis develops two barriers: the Casparian strips establish an apoplastic barrier and suberin lamellae prevent diffusion through the plasma membrane. Suberin is a complex biopolymer and its deposition is highly responsive to the environment. While the enzymatic framework involved in suberin biosynthesis is well characterized, subsequent steps in suberin formation and regulation remained elusive. Recent publications, studying suberin from a cell biological perspective, have enriched our knowledge on suberin transport and polymerization in the cell wall. These studies have also elucidated the molecular mechanisms controlling suberin biosynthesis and regulation as well as its physiological role in plant abiotic and biotic interactions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Suberin is a hydrophobic biopolymer that can be deposited at the periphery of cells, forming protective barriers against biotic and abiotic stress. In roots, suberin forms lamellae at the periphery of endodermal cells where it plays crucial roles in the control of water and mineral transport. Suberin formation is highly regulated by developmental and environmental cues. However, the mechanisms controlling its spatiotemporal regulation are poorly understood. Here, we show that endodermal suberin is regulated independently by developmental and exogenous signals to fine-tune suberin deposition in roots. We found a set of four MYB transcription factors (MYB41, MYB53, MYB92, and MYB93), each of which is individually regulated by these two signals and is sufficient to promote endodermal suberin. Mutation of these four transcription factors simultaneously through genome editing leads to a dramatic reduction in suberin formation in response to both developmental and environmental signals. Most suberin mutants analyzed at physiological levels are also affected in another endodermal barrier made of lignin (Casparian strips) through a compensatory mechanism. Through the functional analysis of these four MYBs, we generated plants allowing unbiased investigation of endodermal suberin function, without accounting for confounding effects due to Casparian strip defects, and were able to unravel specific roles of suberin in nutrient homeostasis., Competing Interests: The authors declare no competing interest., (Copyright © 2021 the Author(s). Published by PNAS.)

Plants need to attune their stress responses to the ongoing developmental programmes to maximize their efficacy. For instance, successful submergence adaptation is often associated with a delicate balance between saving resources and their expenditure to activate measures that allow stress avoidance or attenuation. We observed a significant decrease in submergence tolerance associated with ageing in Arabidopsis thaliana, with a critical step between 2 and 3 weeks of post-germination development. This sensitization to flooding was concomitant with the transition from juvenility to adulthood. Transcriptomic analyses indicated that a group of genes related to abscisic acid and oxidative stress response was more highly expressed in juvenile plants than in adult ones. These genes are induced by the endomembrane tethered transcription factor ANAC017 that was in turn activated by submergence-associated oxidative stress. A combination of molecular, biochemical and genetic analyses showed that these genes are located in genomic regions that move towards a heterochromatic state with adulthood, as marked by lysine 4 trimethylation of histone H3. We concluded that, while the mechanisms of flooding stress perception and signal transduction were unaltered between juvenile and adult phases, the sensitivity that these mechanisms set into action is integrated, via epigenetic regulation, into the developmental programme of the plant., (© 2020 Society for Experimental Biology and John Wiley & Sons Ltd.)

The ability to perceive oxygen levels is crucial to many organisms because it allows discerning environments compatible with aerobic or anaerobic metabolism, as well as enabling rapid switch between these two energy strategies. Organisms from different taxa dedicate distinct mechanisms to associate oxygen fluctuations with biological responses. Following from this observation, we speculated that orthogonal oxygen sensing devices can be created by transfer of essential modules from one species to another in which they are not conserved. We expressed plant cysteine oxidase (PCOs) enzymes in Saccharomyces cerevisiae, to confer oxygen-conditional degradability to a bioluminescent protein tagged with the Cys-exposing N-degron typical of plant ERF-VII factors. Co-translation of a second luciferase protein, not subjected to oxygen-dependent proteolysis, made the resulting Double Luciferase Oxygen Reporter (DLOR) ratiometric. We show that DLOR acts as a proxy for oxygen dynamics in yeast cultures. Moreover, since DLOR activity was enabled by the PCO sensors, we employed this device to disclose some of their properties, such as the dispensability of nitric oxide for N-terminal cysteine oxidation and the individual performance of Arabidopsis PCO isoforms in vivo. In the future, we propose the synthetic DLOR device as a convenient, eukaryotic cell-based tool to easily screen substrates and inhibitors of cysteine oxidase enzymes in vivo. Replacement of the luminescent proteins with fluorescent proteins will further turn our system into a visual reporter for oxygen dynamics in living cells., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

As non-photosynthesizing organs, roots are dependent on diffusion of oxygen from the external environment and, in some instances, from the shoot for their aerobic metabolism. Establishment of hypoxic niches in the developing tissues of plants has been postulated as a consequence of insufficient diffusion of oxygen to satisfy the demands throughout development. Here, we report that such niches are established at specific stages of lateral root primordia development in Arabidopsis thaliana grown under aerobic conditions. Using gain- and loss-of-function mutants, we show that ERF-VII transcription factors, which mediate hypoxic responses, control root architecture by acting in cells with a high level of auxin signaling. ERF-VIIs repress the expression of the auxin-induced genes LBD16, LBD18, and PUCHI, which are essential for lateral root development, by binding to their promoters. Our results support a model in which the establishment of hypoxic niches in the developing lateral root primordia contributes to the shutting down of key auxin-induced genes and regulates the production of lateral roots., (Copyright © 2019 The Author. Published by Elsevier Inc. All rights reserved.)

The Group VII Ethylene Responsive Factors (ERFs-VII) RAP2.2 and RAP2.12 have been mainly characterized with regard to their contribution as activators of fermentation in plants. However, transcriptional changes measured in conditions that stabilize these transcription factors exceed the mere activation of this biochemical pathway, implying additional roles performed by the ERF-VIIs in other processes. We evaluated gene expression in transgenic Arabidopsis lines expressing a stabilized form of RAP2.12, or hampered in ERF-VII activity, and identified genes affected by this transcriptional regulator and its homologs, including some involved in oxidative stress response, which are not universally induced under anaerobic conditions. The contribution of the ERF-VIIs in regulating this set of genes in response to chemically induced or submergence-stimulated mitochondria malfunctioning was found to depend on the plant developmental stage. A similar age-dependent mechanism also restrained ERF-VII activity upon the core-hypoxic genes, independently of the N-end rule pathway, which is accounted for the control of the anaerobic response. To conclude, this study shed new light on a dual role of ERF-VII proteins under submergence: as positive regulators of the hypoxic response and as repressors of oxidative-stress related genes, depending on the developmental stage at which plants are challenged by stress conditions., (© 2017 John Wiley & Sons Ltd.)

Approaches enabling efficient phosphorus utilization in crops are of great importance. In cereal crop like wheat, utilization of inorganic phosphate (Pi) is high and mature grains are the major sink for Pi utilization and storage. Research that addresses the importance of the Pi homeostasis in developing grains is limited. In an attempt to understand the Pi homeostasis in developing wheat grains, we identified twelve new phosphate transporters (PHT), these are phyologentically well distributed along with the members reported from Arabidopsis and rice. Enhanced expression of PHT1-subfamily genes was observed in roots subjected to the Pi starvation suggesting their active role in Pi homeostasis. Differential expression patterns of all the PHT genes during grain filling stages suggested their importance in the filial tissues. Additionally, high accumulation of Pi and total P in aleurone correlates well with the expression of TaPHTs and other phosphate starvation related genes. Tissue specific transcript accumulation of TaPHT1.1, TaPHT1.2, TaPHT1.4 in aleurone; TaPHT3.1 in embryo and TaPHT4.2 in the endosperm was observed. Furthermore, their transcript abundance was affected in low phytate wheat grains. Altogether, this study helps in expanding the knowledge and prioritize the candidate wheat Pi-transporters to modulate the Pi homeostasis in cereal grains.

Initial steps of aspartate-derived biosynthesis pathway (Asp pathway) producing Lys, Thr, Met and Ile are catalyzed by bifunctional (AK/HSD) and monofunctional (AK-lys) aspartate kinase (AK) enzymes. Here, we show that transcription of all AK genes is negatively regulated under darkness and low sugar conditions. By using yeast one-hybrid assays and complementary chromatin immunoprecipitation analyses in Arabidopsis cells, the bZIP transcription factors ABI5 and DPBF4 were identified, capable of interacting with the G-box-containing enhancer of AK/HSD1 promoter. Elevated transcript levels of DPBF4 and ABI5 under darkness and low sugar conditions coincide with the repression of AK gene expression. Overexpression of ABI5, but not DPBF4, further increases this AK transcription suppression. Concomitantly, it also increases the expression of asparagines synthetase 1 (ASN1) that shifts aspartate utilization towards asparagine formation. However, in abi5 or dpbf4 mutant and abi5, dpbf4 double mutant the repression of AK expression is maintained, indicating a functional redundancy with other bZIP-TFs. A dominant-negative version of DPBF4 fused to the SRDX repressor domain of SUPERMAN could counteract the repression and stimulate AK expression under low sugar and darkness in planta. This effect was verified by showing that DPBF4-SRDX fails to recognize the AK/HSD1 enhancer sequence in yeast one-hybrid assays, but increases heterodimmer formation with DPBF4 and ABI5, as estimated by yeast two-hybrid assays. Hence it is likely that heterodimerization with DPBF4-SRDX inhibits the binding of redundantly functioning bZIP-TFs to the promoters of AK genes and thereby releases the repressing effect. These data highlight a novel transcription control of the chloroplast aspartate pathway that operates under energy limiting conditions.

To assist in the analysis of plant gene functions we have generated a new Arabidopsis insertion mutant collection of 90 000 lines that carry the T-DNA of Agrobacterium gene fusion vector pPCV6NFHyg. Segregation analysis indicates that the average frequency of insertion sites is 1.29 per line, predicting about 116 100 independent tagged loci in the collection. The average T-DNA copy number estimated by Southern DNA hybridization is 2.4, as over 50% of the insertion loci contain tandem T-DNA copies. The collection is pooled in two arrays providing 40 PCR templates, each containing DNA from either 4000 or 5000 individual plants. A rapid and sensitive PCR technique using high-quality template DNA accelerates the identification of T-DNA tagged genes without DNA hybridization. The PCR screening is performed by agarose gel electrophoresis followed by isolation and direct sequencing of DNA fragments of amplified T-DNA insert junctions. To estimate the mutation recovery rate, 39 700 lines have been screened for T-DNA tags in 154 genes yielding 87 confirmed mutations in 73 target genes. Screening the whole collection with both T-DNA border primers requires 170 PCR reactions that are expected to detect a mutation in a gene with at least twofold redundancy and an estimated probability of 77%. Using this technique, an M2 family segregating a characterized gene mutation can be identified within 4 weeks.

FLOWERING LOCUS T (FT), which acts in parallel with the meristem-identity gene LEAFY (LFY) to induce flowering of Arabidopsis, was isolated by activation tagging. Like LFY, FT acts partially downstream of CONSTANS (CO), which promotes flowering in response to long days. Unlike many other floral regulators, the deduced sequence of the FT protein does not suggest that it directly controls transcription or transcript processing. Instead, it is similar to the sequence of TERMINAL FLOWER 1 (TFL1), an inhibitor of flowering that also shares sequence similarity with membrane-associated mammalian proteins.