Summary
Phosphate (Pi) is a critical macronutrient for the biochemical and molecular functions of cells. Under phosphate limitation, plants manifest adaptative strategies to increase phosphate ...scavenging. However, how low phosphate sensing links to the transcriptional machinery remains unknown.
The role of the MEDIATOR (MED) transcriptional co‐activator, through its MED16 subunit in Arabidopsis root system architecture remodeling in response to phosphate limitation was assessed. Its critical function acting over the SENSITIVE TO PROTON RHIZOTOXICITY1 (STOP1)‐ALUMINUM‐ACTIVATED MALATE TRANSPORT1 (ALMT1) signaling module was tested through a combination of genetic, biochemical, and genome‐wide transcriptomic approaches.
Root system configuration in response to phosphate scarcity involved MED16 functioning, which modulates the expression of a large set of low‐phosphate‐induced genes that respond to local and systemic signals in the Arabidopsis root tip, including those directly activated by STOP1. Biomolecular fluorescence complementation analysis suggests that MED16 is required for the transcriptional activation of STOP1 targets, including the membrane permease ALMT1, to increase malate exudation in response to low phosphate.
Our results unveil the function of a critical transcriptional component, MED16, in the root adaptive responses to a scarce plant macronutrient, which helps understanding how plant cells orchestrate root morphogenesis to gene expression with the STOP1‐ALMT1 module.
Nitrate distribution in soils is often heterogeneous. Plants have adapted to this by modifying their root system architecture (RSA). Previous studies showed that NITRATE-TRANSPORTER1.1 (NRT1.1), ...which also transports auxin, helps inhibit lateral root primordia (LRP) emergence in nitrate-poor patches, by preferentially transporting auxin away from the LRP. In this study, we identified the regulatory system for this response involving the transcription factor (TF), SENSITIVE-TO-PROTON-RHIZOTOXICITY1 (STOP1), which is accumulated in the nuclei of LRP cells under nitrate deficiency and directly regulates Arabidopsis
expression. Mutations in
mimic the root phenotype of the loss-of-function
mutant under nitrate deficiency, compared to wild-type plants, including increased LR growth and higher
activity (i.e., higher LRP auxin signaling/activity). Nitrate deficiency-induced LR growth inhibition was almost completely reversed when STOP1 and the TF, TEOSINTE-BRANCHED1,-CYCLOIDEA,-PCF-DOMAIN-FAMILY-PROTEIN20 (TCP20), a known activator of
expression, were both mutated. Thus, the STOP1-TCP20 system is required for activation of
expression under nitrate deficiency, leading to reduced LR growth in nitrate-poor regions. We found this STOP1-mediated system is more active as growth media becomes more acidic, which correlates with reductions in soil nitrate as the soil pH becomes more acidic. STOP1 has been shown to be involved in RSA modifications in response to phosphate deficiency and increased potassium uptake, hence, our findings indicate that root growth regulation in response to low availability of the major fertilizer nutrients, nitrogen, phosphorus and potassium, all involve STOP1, which may allow plants to maintain appropriate root growth under the complex and varying soil distribution of nutrients.
Abstract
Malate efflux from roots, which is regulated by the transcription factor STOP1 (SENSITIVE-TO-PROTON-RHIZOTOXICITY1) and mediates aluminum-induced expression of ...ALUMINUM-ACTIVATED-MALATE-TRANSPORTER1 (AtALMT1), is critical for aluminum resistance in Arabidopsis thaliana. Several studies showed that AtALMT1 expression in roots is rapidly observed in response to aluminum; this early induction is an important mechanism to immediately protect roots from aluminum toxicity. Identifying the molecular mechanisms that underlie rapid aluminum resistance responses should lead to a better understanding of plant aluminum sensing and signal transduction mechanisms. In this study, we observed that GFP-tagged STOP1 proteins accumulated in the nucleus soon after aluminum treatment. The rapid aluminum-induced STOP1-nuclear localization and AtALMT1 induction were detected in the presence of a protein synthesis inhibitor, suggesting that post-translational regulation is involved in these events. STOP1 also regulated rapid aluminum-induced expression for other genes that carry a functional/high-affinity STOP1-binding site in their promoter, including STOP2, GLUTAMATE-DEHYDROGENASE1 and 2 (GDH1 and 2). However STOP1 did not regulate Al resistance genes which have no functional STOP1-binding site such as ALUMINUM-SENSITIVE3, suggesting that the binding of STOP1 in the promoter is essential for early induction. Finally, we report that GDH1 and 2 which are targets of STOP1, are novel aluminum-resistance genes in Arabidopsis.
STOP1 nuclear-localization and its high affinity binding to target gene promoters are essential for early aluminum-induced gene expression, with GDH1/2 being novel Arabidopsis Al-tolerance genes.
Low phosphate (Pi) availability constrains plant development and seed production in both natural and agricultural ecosystems. When Pi is scarce, modifications of root system architecture (RSA) ...enhance the soil exploration ability of the plant and lead to an increase in Pi uptake. In Arabidopsis, an iron-dependent mechanism reprograms primary root growth in response to low Pi availability. This program is activated upon contact of the root tip with low-Pi media and induces premature cell differentiation and the arrest of mitotic activity in the root apical meristem, resulting in a short-root phenotype. However, the mechanisms that regulate the primary root response to Pilimiting conditions remain largely unknown. Here we report on the isolation and characterization of two low-Pi insensitive mutants (lpi5 and lpi6), which have a long-root phenotype when grown in low-Pi media. Cellular, genomic, and transcriptomic analysis of low-Pi insensitive mutants revealed that the genes previously shown to underlie Arabidopsis Al tolerance via root malate exudation, known as SENSITIVE TO PROTON RHIZOTOXICITY (STOP1) and ALUMINUM ACTIVATED MALATE TRANSPORTER 1 (ALMT1), represent a critical checkpoint in the root developmental response to Pi starvation in Arabidopsis thaliana. Our results also show that exogenous malate can rescue the long-root phenotype of lpi5 and lpi6. Malate exudation is required for the accumulation of Fe in the apoplast of meristematic cells, triggering the differentiation of meristematic cells in response to Pi deprivation.
Low inorganic phosphate (Pi) availability causes terminal differentiation of the root apical meristem (RAM), a phenomenon known as root meristem exhaustion or determined growth. Here, we report that ...the CLE14 peptide acts as a key player in this process. Low Pi stress induces iron mobilization in the RAM through the action of LPR1/LPR2, causing expression of CLE14 in the proximal meristem region. CLV2 and PEPR2 receptors perceive CLE14 and trigger RAM differentiation, with concomitant downregulation of SHR/SCR and PIN/AUXIN pathway. Our results reveal multiple steps of the molecular mechanism of one of the most physiologically important root nutrient responses.
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•CLE14 peptide is a component of the Pi starvation response•CLE14 is the signal that triggers full root meristem differentiation in low Pi•CLE14 acts downstream of LOW PHOSPHATE ROOT1/LOW PHOSPHATE ROOT2 (LPR1/LPR2)•CLE14 triggers full root meristem differentiation through CLV2/PEPR2 receptors
Phosphorus limitation profoundly affects root development in Arabidopsis thaliana. Gutiérrez-Alanís et al. show that in response to low Pi, CLE14 peptide is expressed in proximal meristem, is perceived by CLV2 and PEPR2 receptors, and causes differentiation of surrounding RAM, leading to root meristem exhaustion.
Embryonic development represents an important reproductive phase of sexually reproducing plant species. The fusion of egg and sperm produces the plant zygote, a totipotent cell that, through cell ...division and cell identity specification in early embryogenesis, establishes the major cell lineages and tissues of the adult plant. The subsequent morphogenesis phase produces the full-sized embryo, while the late embryogenesis maturation process prepares the seed for dormancy and subsequent germination, ensuring continuation of the plant life cycle. In this review on embryogenesis, we compare the model eudicot Arabidopsis thaliana with monocot crops, focusing on genome activation, paternal and maternal regulation of early zygote development, and key organizers of patterning, such as auxin and WOX transcription factors. While the early stages of embryo development are apparently conserved among plant species, embryo maturation programs have diversified between eudicots and monocots. This diversification in crop species reflects the likely effects of domestication on seed quality traits that are determined during embryo maturation, and also assures seed germination in different environmental conditions. This review describes the most important features of embryonic development in plants, and the scope and applications of genomics in plant embryo studies.
During plant embryogenesis, developmentally specified patterning and morphogenesis define embryonic programs. In recent years, significant advances have been made using Arabidopsis that revealed important insights into these key biological programs. This review presents recent progress in transcriptomic and genomic studies of embryo development in Arabidopsis, dicot, and monocot crop species and discusses findings implications to prospects in crop seeds.
Summary
Phosphate (Pi)‐deficient soils are a major limitant factor for crop production in many regions of the world. Despite that plants have innovated several developmental and biochemical ...strategies to deal with this stress, there are still massive extensions of land which combine several abiotic stresses, including phosphate starvation, that limit their use for plant growth and food production. In several plant species, a genetic programme underlies the biochemical and developmental responses of the organism to cope with low phosphate (Pi) availability. Both protein‐ and miRNA‐coding genes involved in the adaptative response are transcriptionally activated upon Pi starvation. Several of the responsive genes have been identified as transcriptional targets of PHR1, a transcription factor that binds a conserved cis‐element called PHR1‐binding site (P1BS). Our group has previously described and characterized a minimal genetic arrangement that includes two P1BS elements, as a phosphate‐responsive enhancer (EZ2). Here, we report the engineering and successful use of a phosphate‐dependent bidirectional promoter, which has been designed and constructed based on the palindromic sequences of the two P1BS elements present in EZ2. This bidirectional promoter has a potential use in both plant in vitro approaches and in the generation of improved crops adapted to Pi starvation and other abiotic stresses.
Nutrient-efficient root system architecture (RSA) is becoming an important breeding objective for generating crop varieties with improved nutrient and water acquisition efficiency. Genetic variants ...shaping soybean RSA is key in improving nutrient and water acquisition. Here, we report on the use of an improved 2-dimensional high-throughput root phenotyping platform that minimizes background noise by imaging pouch-grown root systems submerged in water. We also developed a background image cleaning Python pipeline that computationally removes images of small pieces of debris and filter paper fibers, which can be erroneously quantified as root tips. This platform was used to phenotype root traits in 286 soybean lines genotyped with 5.4 million single-nucleotide polymorphisms. There was a substantially higher correlation in manually counted number of root tips with computationally quantified root tips (95% correlation), when the background was cleaned of nonroot materials compared to root images without the background corrected (79%). Improvements in our RSA phenotyping pipeline significantly reduced overestimation of the root traits influenced by the number of root tips. Genome-wide association studies conducted on the root phenotypic data and quantitative gene expression analysis of candidate genes resulted in the identification of 3 putative positive regulators of root system depth, total root length and surface area, and root system volume and surface area of thicker roots (
DOF1-like
zinc finger transcription factor, protein of unknown function, and C2H2 zinc finger protein). We also identified a putative negative regulator (gibberellin 20 oxidase 3) of the total number of lateral roots.
Abstract Antagonism between unrelated plant viruses has not been thoroughly described. Our studies show that two unrelated viruses, papaya ringspot virus (PRSV) and papaya mosaic virus (PapMV) ...produce different symptomatic outcomes during mixed infection depending on the inoculation order. Synergism occurs in plants infected first with PRSV or in plants infected simultaneously with PRSV and PapMV, and antagonism occurs in plants infected first with PapMV and later inoculated with PRSV. During antagonism, elevated pathogenesis-related (PR-1) gene expression and increased reactive oxygen species production indicated the establishment of a host defense resulting in the reduction in PRSV titers. Polyribosomal fractioning showed that PRSV affects translation of cellular eEF1α, PR-1, β-tubulin, and PapMV RNAs in planta , suggesting that its infection could be related to an imbalance in the translation machinery. Our data suggest that primary PapMV infection activates a defense response against PRSV and establishes a protective relationship with the papaya host.
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