Arabidopsis AUX1 gene: a permease-like regulator of root gravitropism

Molecular hydrogen positively influences root gravitropism involving auxin signaling and starch accumulation

Although geoscience of natural hydrogen (H2), hydrogen-producing soil bacteria, and especially plant-based H2, has been observed, it is not clear whether or how above H2 resources influence root gravitropic responses. Here, pharmacological, genetic, molecular, and cell biological tools were applied to investigate how plant-based H2 coordinates gravity responses in Arabidopsis roots. Since roots show higher H2 production than shoots, exogenous H2 supply was used to mimic this function. After H2 supplementation, the asymmetric expression of the auxin-response reporter DR5 driven by auxin influx and efflux carriers, and thereafter positive root gravitropism were observed. These positive responses in root gravitropism were sensitive to auxin polar transport inhibitors, and importantly, the defective phenotypes observed in aux1-7, pin1, and pin2 mutants were not significantly altered by exogenous H2. The observed starch accumulation was matched with the reprogramming gene expression linked to starch synthesis and degradation. Transgenic plants expressing hydrogenase1 (CrHYD1) from Chlamydomonas reinhardtii not only displayed higher endogenous H2 concentrations, the inducible AUX1 gene expression and starch accumulation, but also showed pronounced root gravitropism. Collectively, above evidence preliminarily provides a framework for understanding the molecular basis of the possible functions of both plant/soil-based and nature H2 in root architecture.

Genetic Basis of Tillering Angle from Other Plants to Wheat: Current Progress and Future Perspectives

Plant architecture is an important agronomic trait that impacts crop yield. The tiller angle is a critical aspect of the plant's structural organization, which is influenced by both internal and external factors. The genetic mechanisms underlying the tiller angle have been extensively investigated in other plants. However, research on wheat is relatively limited. Additionally, mechanics has emerged as a connection between biochemical signaling and the development of three-dimensional biological forms. It not only reveals how physical interactions at the cellular level influence overall morphogenesis but also elucidates the interplay between these mechanical processes and molecular signaling pathways that collectively determine plant morphology. This review examines the recent advancements in the study of tillering angle in wheat and other plants. It discusses progress in research ranging from observable characteristics to the regulation of genes, as well as the physiological and biochemical aspects, and the adaptability to environmental factors. In addition, this review also discusses the effects of mechanical on plant growth and development, and provides ideas for the study of mechanical regulation mechanism of tillering angle in wheat. Consequently, based on the research of other plants and combined with the genetic and mechanical principles, this approach offers novel insights and methodologies for studying tillering in wheat. This interdisciplinary research framework not only enhances our understanding of the mechanisms underlying wheat growth and development but may also uncover the critical factors that regulate tillering angle, thereby providing a scientific foundation for improving wheat yield and adaptability.

Over 25 years of decrypting PIN-mediated plant development

Identification of PIN exporters for auxin, the major coordinative signal in plants, some 25 years ago, signifies a landmark in our understanding of plant-specific mechanisms underlying development and adaptation. Auxin is directionally transported throughout the plant body; a unique feature already envisioned by Darwin and solidified by PINs' discovery and characterization. The PIN-based auxin distribution network with its complex regulations of PIN expression, localization and activity turned out to underlie a remarkable multitude of developmental processes and represents means to integrate endogenous and environmental signals. Given the recent anniversary, we here summarize past and current developments in this exciting field.

A molecular perspective on the role of FERONIA in root growth, nutrient uptake, stress sensing and microbiome assembly

BACKGROUND

Roots perform multifaceted functions in plants such as movement of nutrients and water, sensing stressors, shaping microbiome, and providing structural support. How roots perceive and respond above traits at the molecular level remains largely unknown. Despite the enormous advancements in crop improvement, the majority of recent efforts have concentrated on above-ground traits leaving significant knowledge gaps in root biology. Also, studying root system architecture (RSA) is more difficult due to its intricacy and the difficulties of observing them during plant life cycle which has made it difficult to identify desired root traits for the crop improvement. However, with the aid of high-throughput phenotyping and genotyping tools many developmental and stress-mediated regulation of RSA has emerged in both model and crop plants leading to new insights in root biology. Our current understanding of upstream signaling events (cell wall, apoplast) in roots and how they are interconnected with downstream signaling cascades has largely been constrained by the fact that most research in plant systems concentrate on cytosolic signal transduction pathways while ignoring the early perception by cells' exterior parts. In this regard, we discussed the role of FERONIA (FER) a cell wall receptor-like kinase (RLK) which acts as a sensor and a bridge between apoplast and cytosolic signaling pathways in root biology.

AIM OF THE REVIEW

The goal of this review is to provide valuable insights into present understanding and future research perspectives on how FER regulates distinct root responses related to growth and stress adaptation.

KEY SCIENTIFIC CONCEPTS OF REVIEW

In plants, FER is a unique RLK because it can act as a multitasking sensor and regulates diverse growth, and adaptive traits. In this review, we mainly highlighted its role in root biology like how it modulates distinct root responses such as root development, sensing abiotic stressors, mechanical stimuli, nutrient transport, and shaping microbiome. Further, we provided an update on how FER controls root traits by involving Rapid Alkalinization Factor (RALF) peptides, calcium, reactive oxygen species (ROS) and hormonal signaling pathways.. We also highlight number of outstanding questions in FER mediated root responses that warrants future investigation. To sum up, this review provides a comprehsive information on the role of FER in root biology which can be utilized for the development of future climate resilient and high yielding crops based on the modified root system.

Slow release of a synthetic auxin induces formation of adventitious roots in recalcitrant woody plants

Clonal propagation of plants by induction of adventitious roots (ARs) from stem cuttings is a requisite step in breeding programs. A major barrier exists for propagating valuable plants that naturally have low capacity to form ARs. Due to the central role of auxin in organogenesis, indole-3-butyric acid is often used as part of commercial rooting mixtures, yet many recalcitrant plants do not form ARs in response to this treatment. Here we describe the synthesis and screening of a focused library of synthetic auxin conjugates in Eucalyptus grandis cuttings and identify 4-chlorophenoxyacetic acid-L-tryptophan-OMe as a competent enhancer of adventitious rooting in a number of recalcitrant woody plants, including apple and argan. Comprehensive metabolic and functional analyses reveal that this activity is engendered by prolonged auxin signaling due to initial fast uptake and slow release and clearance of the free auxin 4-chlorophenoxyacetic acid. This work highlights the utility of a slow-release strategy for bioactive compounds for more effective plant growth regulation.

The auxin efflux carrier PIN1a regulates vascular patterning in cereal roots

Barley (Hordeum vulgare) is an important global cereal crop and a model in genetic studies. Despite advances in characterising barley genomic resources, few mutant studies have identified genes controlling root architecture and anatomy, which plays a critical role in capturing soil resources. Our phenotypic screening of a TILLING mutant collection identified line TM5992 exhibiting a short-root phenotype compared with wild-type (WT) Morex background. Outcrossing TM5992 with barley variety Proctor and subsequent SNP array-based bulk segregant analysis, fine mapped the mutation to a cM scale. Exome sequencing pinpointed a mutation in the candidate gene HvPIN1a, further confirming this by analysing independent mutant alleles. Detailed analysis of root growth and anatomy in Hvpin1a mutant alleles exhibited a slower growth rate, shorter apical meristem and striking vascular patterning defects compared to WT. Expression and mutant analyses of PIN1 members in the closely related cereal brachypodium (Brachypodium distachyon) revealed that BdPIN1a and BdPIN1b were redundantly expressed in root vascular tissues but only Bdpin1a mutant allele displayed root vascular defects similar to Hvpin1a. We conclude that barley PIN1 genes have sub-functionalised in cereals, compared to Arabidopsis (Arabidopsis thaliana), where PIN1a sequences control root vascular patterning.

Diverse geotropic responses in the orchid family

In epiphytes, aerial roots are important to combat water-deficient, nutrient-poor, and high-irradiance microhabitats. However, whether aerial roots can respond to gravity and whether auxin plays a role in regulating aerial root development remain open-ended questions. Here, we investigated the gravitropic response of the epiphytic orchid Phalaenopsis aphrodite. Our data showed that aerial roots of P. aphrodite failed to respond to gravity, and this was correlated with a lack of starch granules/statolith sedimentation in the roots and the absence of the auxin efflux carrier PIN2 gene. Using an established auxin reporter, we discovered that auxin maximum was absent in the quiescent center of aerial roots of P. aphrodite. Also, gravity failed to trigger auxin redistribution in the root caps. Hence, loss of gravity sensing and gravity-dependent auxin redistribution may be the genetic factors contributing to aerial root development. Moreover, the architectural and functional innovations that achieve fast gravitropism in the flowering plants appear to be lost in both terrestrial and epiphytic orchids, but are present in the early diverged orchid subfamilies. Taken together, our findings provide physiological and molecular evidence to support the notion that epiphytic orchids lack gravitropism and suggest diverse geotropic responses in the orchid family.

The ectomycorrhizal fungus Scleroderma bovista improves growth of hazelnut seedlings and plays a role in auxin signaling and transport

Introduction

Scleroderma bovista can form symbiotic ectomycorrhizal fungi with hazel roots. The mechanism through which S. bovista promotes hazelnut growth remains unclear.

Methods

This study aimed to evaluate the effect of ectomycorrhizal fungus S. bovista on the growth and development of hazel roots and gene expression changes through comparative transcriptome analysis.

Results

After inoculation with S. bovista, the fungus symbiotically formed ectomycorrhiza with hazel roots. The fresh weights of the aboveground and underground parts of My treatment (inoculated with S. bovista and formed mycorrhiza) were much higher than those of the control, respectively. The length, project area, surface area, volume, forks, and diameter of the inoculated seedlings root were 1.13 to 2.48 times higher than those of the control. In the paired comparison, 3,265 upregulated and 1,916 downregulated genes were identified. The most significantly enriched Gene Ontology term for the upregulated Differentially Expressed Genes was GO:0005215 (transporter activity). Immunohistochemical analysis suggested that the expression levels of auxin and Auxin Response Factor9 were significantly increased by S. bovista after the formation of mycorrhizal fungi in hazelnut root tips.

Discussion

These results indicate that genes related to auxin biosynthesis, transport and signaling, and transport of nutrients may contribute to root development regulation in hazel ectomycorrhiza.

Structure and Function of Auxin Transporters

Auxins, a group of central hormones in plant growth and development, are transported by a diverse range of transporters with distinct biochemical and structural properties. This review summarizes the current knowledge on all known auxin transporters with respect to their biochemical and biophysical properties and the methods used to characterize them. In particular, we focus on the recent advances that were made concerning the PIN-FORMED family of auxin exporters. Insights derived from solving their structures have improved our understanding of the auxin export process, and we discuss the current state of the art on PIN-mediated auxin transport, including the use of biophysical methods to examine their properties. Understanding the mechanisms of auxin transport is crucial for understanding plant growth and development, as well as for the development of more effective strategies for crop production and plant biotechnology.

Ethylene regulates auxin-mediated root gravitropic machinery and controls root angle in cereal crops

Root angle is a critical factor in optimizing the acquisition of essential resources from different soil depths. The regulation of root angle relies on the auxin-mediated root gravitropism machinery. While the influence of ethylene on auxin levels is known, its specific role in governing root gravitropism and angle remains uncertain, particularly when Arabidopsis (Arabidopsis thaliana) core ethylene signaling mutants show no gravitropic defects. Our research, focusing on rice (Oryza sativa L.) and maize (Zea mays), clearly reveals the involvement of ethylene in root angle regulation in cereal crops through the modulation of auxin biosynthesis and the root gravitropism machinery. We elucidated the molecular components by which ethylene exerts its regulatory effect on auxin biosynthesis to control root gravitropism machinery. The ethylene-insensitive mutants ethylene insensitive2 (osein2) and ethylene insensitive like1 (oseil1), exhibited substantially shallower crown root angle compared to the wild type. Gravitropism assays revealed reduced root gravitropic response in these mutants. Hormone profiling analysis confirmed decreased auxin levels in the root tips of the osein2 mutant, and exogenous auxin (NAA) application rescued root gravitropism in both ethylene-insensitive mutants. Additionally, the auxin biosynthetic mutant mao hu zi10 (mhz10)/tryptophan aminotransferase2 (ostar2) showed impaired gravitropic response and shallow crown root angle phenotypes. Similarly, maize ethylene-insensitive mutants (zmein2) exhibited defective gravitropism and root angle phenotypes. In conclusion, our study highlights that ethylene controls the auxin-dependent root gravitropism machinery to regulate root angle in rice and maize, revealing a functional divergence in ethylene signaling between Arabidopsis and cereal crops. These findings contribute to a better understanding of root angle regulation and have implications for improving resource acquisition in agricultural systems.

Multi-scale mechanisms driving root regeneration: From regeneration competence to tissue repatterning

Plants possess an outstanding capacity to regenerate enabling them to repair damages caused by suboptimal environmental conditions, biotic attacks, or mechanical damages impacting the survival of these sessile organisms. Although the extent of regeneration varies greatly between localized cell damage and whole organ recovery, the process of regeneration can be subdivided into a similar sequence of interlinked regulatory processes. That is, competence to regenerate, cell fate reprogramming, and the repatterning of the tissue. Here, using root tip regeneration as a paradigm system to study plant regeneration, we provide a synthesis of the molecular responses that underlie both regeneration competence and the repatterning of the root stump. Regarding regeneration competence, we discuss the role of wound signaling, hormone responses and synthesis, and rapid changes in gene expression observed in the cells close to the cut. Then, we consider how this rapid response is followed by the tissue repatterning phase, where cells experience cell fate changes in a spatial and temporal order to recreate the lost stem cell niche and columella. Lastly, we argue that a multi-scale modeling approach is fundamental to uncovering the mechanisms underlying root regeneration, as it allows to integrate knowledge of cell-level gene expression, cell-to-cell transport of hormones and transcription factors, and tissue-level growth dynamics to reveal how the bi-directional feedbacks between these processes enable self-organized repatterning of the root apex.

Hydrotropism mechanisms and their interplay with gravitropism

Plants partly optimize their water recruitment from the growth medium by directing root growth toward a moisture source, a phenomenon termed hydrotropism. The default mechanism of downward growth, termed gravitropism, often functions to counteract hydrotropism when the water-potential gradient deviates from the gravity vector. This review addresses the identity of the root sites in which hydrotropism-regulating factors function to attenuate gravitropism and the interplay between these various factors. In this context, the function of hormones, including auxin, abscisic acid, and cytokinins, as well as secondary messengers, calcium ions, and reactive oxygen species in the conflict between these two opposing tropisms is discussed. We have assembled the available data on the effects of various chemicals and genetic backgrounds on both gravitropism and hydrotropism, to provide an up-to-date perspective on the interactions that dictate the orientation of root tip growth. We specify the relevant open questions for future research. Broadening our understanding of root mechanisms of water recruitment holds great potential for providing advanced approaches and technologies that can improve crop plant performance under less-than-optimal conditions, in light of predicted frequent and prolonged drought periods due to global climate change.

Investigation of biological-rhythm patterns: physiological and biochemical effects in herbaceous plants exposed to low-level chronic radiation - part 1: nonirradiated seeds

HYPOTHESIS

Because reactive oxygen species are involved in the regulation of biological rhythms, we hypothesized that intra-annual variability of seed progeny quality at low doses of ionizing radiation (LDIRs) would differ from that of background plants.

MATERIALS AND METHODS

We conducted 12 consecutive experiments using the roll culture method by germinating seeds (monthly for 3 weeks) of six herbaceous plant species (Bromus inermis, Geum aleppicum, Plantago major, Rumex confertus, Silene latifolia, and Taraxacum officinale) growing under conditions of chronic radiation in the East Ural Radioactive Trace (EURT). We assessed physiological (seed viability and abnormality frequency) and biochemical (low-molecular-weight antioxidants, LMWAs) parameters of seedlings.

RESULTS

Total absorbed dose rates of maternal plants (TADRplants) and seed embryos (TADRseeds) in the EURT exceeded background levels by 1-3 and 1-2 orders of magnitude, respectively. Nonlinear dependencies on TADR were mainly characteristic of physiological and biochemical parameters. For most populations of the studied species (B. inermis, G. aleppicum, R. confertus, and S. latifolia), seedling survival and root length decreased in the autumn-winter period, while the frequency of abnormal seedlings increased. The content of LMWAs could be ranked as R. confertus > B. inermis > G. aleppicum > S. latifolia, in good agreement with the presence of anthocyanin pigmentation in the plants. The lowest synthesis of antioxidants in seedlings was observed in winter. A high LMWA content promoted growth and reduced the frequency of abnormal seedlings.

CONCLUSIONS

These results underscore a multistage nature of the impact of LDIRs on intra-annual biological rhythms in plants. High heterogeneity in reference group 'wild grasses' and diversity of their radiobiological effects should help to develop methods of radiation protection for natural ecosystems and facilitate approaches used by the International Commission on Radiological Protection.HighlightsAbsorbed dose rates for six plant species in the East Ural Radioactive Trace (EURT) area range from 0.11 to 73.89 µGy h-s (plants) and 0.11 to 6.88 µGy h-s (seed embryos).Intra-annual rhythms of physiological and biochemical parameters in the EURT zone differ from those in background seedlings.Plants in the EURT area exhibit a wide range of trait variability, asynchrony of the manifestation of the effects, nonlinear dose-response relations, and hormesis.A high content of low-molecular-weight antioxidants (LMWAs) is associated with low frequency of developmental abnormalities and high viability of seed progeny.

An auxin research odyssey: 1989-2023

The phytohormone auxin is at times called the master regulator of plant processes and has been shown to be a central player in embryo development, the establishment of the polar axis, early aspects of seedling growth, as well as growth and organ formation during later stages of plant development. The Plant Cell has been key, since the inception of the journal, to developing an understanding of auxin biology. Auxin-regulated plant growth control is accomplished by both changes in the levels of active hormones and the sensitivity of plant tissues to these concentration changes. In this historical review, we chart auxin research as it has progressed in key areas and highlight the role The Plant Cell played in these scientific developments. We focus on understanding auxin-responsive genes, transcription factors, reporter constructs, perception, and signal transduction processes. Auxin metabolism is discussed from the development of tryptophan auxotrophic mutants, the molecular biology of conjugate formation and hydrolysis, indole-3-butyric acid metabolism and transport, and key steps in indole-3-acetic acid biosynthesis, catabolism, and transport. This progress leads to an expectation of a more comprehensive understanding of the systems biology of auxin and the spatial and temporal regulation of cellular growth and development.

Trichoderma-secreted anthranilic acid promotes lateral root development via auxin signaling and RBOHF-induced endodermal cell wall remodeling

Trichoderma spp. have evolved the capacity to communicate with plants by producing various secondary metabolites (SMs). Nonhormonal SMs play important roles in plant root development, while specific SMs from rhizosphere microbes and their underlying mechanisms to control plant root branching are still largely unknown. In this study, a compound, anthranilic acid (2-AA), is identified from T. guizhouense NJAU4742 to promote lateral root development. Further studies demonstrate that 2-AA positively regulates auxin signaling and transport in the canonical auxin pathway. 2-AA also partly rescues the lateral root numbers of CASP1pro:shy2-2, which regulates endodermal cell wall remodeling via an RBOHF-induced reactive oxygen species burst. In addition, our work reports another role for microbial 2-AA in the regulation of lateral root development, which is different from its better-known role in plant indole-3-acetic acid biosynthesis. In summary, this study identifies 2-AA from T. guizhouense NJAU4742, which plays versatile roles in regulating plant root development.

The microRNA7833-AUX6 module plays a critical role in wood development by modulating cellular auxin influx in Populus tomentosa

The critical role of auxin on secondary vascular development in woody plants has been demonstrated. The concentration gradient of endogenous indole-3-acetic acid and the cellular and molecular pathways contributing to the auxin-directed vascular organization and wood growth have been uncovered in recent decades. However, our understanding of the roles and regulations of auxin influx in wood formation in trees remains limited. Here, we reported that a microRNA, miR7833, participates in the negative regulation of stem cambial cell division and secondary xylem development in Populus tomentosa. The miR7833 is mainly expressed in the vascular cambium during stem radical growth and specifically targets and represses two AUX/LAX family auxin influx carriers, AUX5 and AUX6, in poplar. We further revealed that poplar AUX6, the most abundant miR7833 target in the stem, is preferentially enriched in the developing xylem and is a positive regulator for cell division and differentiation events during wood formation. Moreover, inhibition of auxin influx carriers by 1-naphthoxyacetic acids abolished the regulatory effects of miR7833 and AUX6 on secondary xylem formation in poplar. Our results revealed the essential roles of the miR7833-AUX6 module in regulating cellular events in secondary xylem development and demonstrated an auxin influx-dependent mechanism for wood formation in poplar.

Genome-wide identification of AAAP gene family and expression analysis in response to saline-alkali stress in foxtail millet (Setaria italica L.)

Amino acid/auxin permease (AAAP) genes encode a large family of protein transporters that play important roles in various aspects of plant growth and development. Here, we performed genome-wide identification of members in the foxtail millet (Setaria italica L.) AAAP family (SiAAAP) and their saline-alkali stress-induced expression patterns, resulting in the identification of 65 SiAAAP genes, which could be divided into eight subfamilies. Except for SiAAAP65, the remaining 64 genes were located on nine chromosomes of foxtail millet. Gene structure and conserved motif analyses indicated that the members in the same subfamily are highly conserved. Gene duplication event analysis suggested that tandem duplication may be the main factor driving the expansion of this gene family, and Ka/Ks analysis indicated that all the duplicated genes have undergone purifying selection. Transcriptome analysis showed differential expression of SiAAAPs in roots, stems, leaves, and tassel inflorescence. Analysis of cis-acting elements in the promoter indicated that SiAAAPs contain stress-responsive cis-acting elements. Under saline-alkali stress, qRT-PCR analysis showed that SiAAP3, SiLHT2, and SiAAP16 were differentially expressed between salt-alkali tolerant millet variety JK3 and salt-alkali sensitive millet variety B175. These results suggest that these genes may be involved in or regulate the response to saline-alkali stress, providing a theoretical basis for further studying the function of SiAAAPs.

Game of thrones among AUXIN RESPONSE FACTORs-over 30 years of MONOPTEROS research

For many years, research has been carried out with the aim of understanding the mechanism of auxin action, its biosynthesis, catabolism, perception, and transport. One central interest is the auxin-dependent gene expression regulation mechanism involving AUXIN RESPONSE FACTOR (ARF) transcription factors and their repressors, the AUXIN/INDOLE-3-ACETIC ACID (Aux/IAA) proteins. Numerous studies have been focused on MONOPTEROS (MP)/ARF5, an activator of auxin-dependent gene expression with a crucial impact on plant development. This review summarizes over 30 years of research on MP/ARF5. We indicate the available analytical tools to study MP/ARF5 and point out the known mechanism of MP/ARF5-dependent regulation of gene expression during various developmental processes, namely embryogenesis, leaf formation, vascularization, and shoot and root meristem formation. However, many questions remain about the auxin dose-dependent regulation of gene transcription by MP/ARF5 and its isoforms in plant cells, the composition of the MP/ARF5 protein complex, and, finally, all the genes under its direct control. In addition, information on post-translational modifications of MP/ARF5 protein is marginal, and knowledge about their consequences on MP/ARF5 function is limited. Moreover, the epigenetic factors and other regulators that act upstream of MP/ARF5 are poorly understood. Their identification will be a challenge in the coming years.

Auxin and abiotic stress responses

Plants are exposed to a variety of abiotic stresses; these stresses have profound effects on plant growth, survival, and productivity. Tolerance and adaptation to stress require sophisticated stress sensing, signaling, and various regulatory mechanisms. The plant hormone auxin is a key regulator of plant growth and development, playing pivotal roles in the integration of abiotic stress signals and control of downstream stress responses. In this review, we summarize and discuss recent advances in understanding the intersection of auxin and abiotic stress in plants, with a focus on temperature, salt, and drought stresses. We also explore the roles of auxin in stress tolerance and opportunities arising for agricultural applications.

Metabolic and Molecular Rearrangements of Sauvignon Blanc (Vitis vinifera L.) Berries in Response to Foliar Applications of Specific Dry Yeast

Dry yeast extracts (DYE) are applied to vineyards to improve aromatic and secondary metabolic compound content and wine quality; however, systematic information on the underpinning molecular mechanisms is lacking. This work aimed to unravel, through a systematic approach, the metabolic and molecular responses of Sauvignon Blanc berries to DYE treatments. To accomplish this, DYE spraying was performed in a commercial vineyard for two consecutive years. Berries were sampled at several time points after the treatment, and grapes were analyzed for sugars, acidity, free and bound aroma precursors, amino acids, and targeted and untargeted RNA-Seq transcriptional profiles. The results obtained indicated that the DYE treatment did not interfere with the technological ripening parameters of sugars and acidity. Some aroma precursors, including cys-3MH and GSH-3MH, responsible for the typical aromatic nuances of Sauvignon Blanc, were stimulated by the treatment during both vintages. The levels of amino acids and the global RNA-seq transcriptional profiles indicated that DYE spraying upregulated ROS homeostatic and thermotolerance genes, as well as ethylene and jasmonic acid biosynthetic genes, and activated abiotic and biotic stress responses. Overall, the data suggested that the DYE reduced berry oxidative stress through the regulation of specific subsets of metabolic and hormonal pathways.

Nitrate, Auxin and Cytokinin-A Trio to Tango

Nitrogen is an important macronutrient required for plant growth and development, thus directly impacting agricultural productivity. In recent years, numerous studies have shown that nitrogen-driven growth depends on pathways that control nitrate/nitrogen homeostasis and hormonal networks that act both locally and systemically to coordinate growth and development of plant organs. In this review, we will focus on recent advances in understanding the role of the plant hormones auxin and cytokinin and their crosstalk in nitrate-regulated growth and discuss the significance of novel findings and possible missing links.

Uncovering early transcriptional regulation during adventitious root formation in Medicago sativa

BACKGROUND

Alfalfa (Medicago sativa L.) as an important legume plant can quickly produce adventitious roots (ARs) to form new plants by cutting. But the regulatory mechanism of AR formation in alfalfa remains unclear.

RESULTS

To better understand the rooting process of alfalfa cuttings, plant materials from four stages, including initial separation stage (C stage), induction stage (Y stage), AR primordium formation stage (P stage) and AR maturation stage (S stage) were collected and used for RNA-Seq. Meanwhile, three candidate genes (SAUR, VAN3 and EGLC) were selected to explore their roles in AR formation. The numbers of differentially expressed genes (DEGs) of Y-vs-C (9,724) and P-vs-Y groups (6,836) were larger than that of S-vs-P group (150), indicating highly active in the early AR formation during the complicated development process. Pathways related to cell wall and sugar metabolism, root development, cell cycle, stem cell, and protease were identified, indicating that these genes were involved in AR production. A large number of hormone-related genes associated with the formation of alfalfa ARs have also been identified, in which auxin, ABA and brassinosteroids are thought to play key regulatory roles. Comparing with TF database, it was found that AP2/ERF-ERF, bHLH, WRKY, NAC, MYB, C2H2, bZIP, GRAS played a major regulatory role in the production of ARs of alfalfa. Furthermore, three identified genes showed significant promotion effect on AR formation.

CONCLUSIONS

Stimulation of stem basal cells in alfalfa by cutting induced AR production through the regulation of various hormones, transcription factors and kinases. This study provides new insights of AR formation in alfalfa and enriches gene resources in crop planting and cultivation.

The birth of a giant: evolutionary insights into the origin of auxin responses in plants

The plant signaling molecule auxin is present in multiple kingdoms of life. Since its discovery, a century of research has been focused on its action as a phytohormone. In land plants, auxin regulates growth and development through transcriptional and non-transcriptional programs. Some of the molecular mechanisms underlying these responses are well understood, mainly in Arabidopsis. Recently, the availability of genomic and transcriptomic data of green lineages, together with phylogenetic inference, has provided the basis to reconstruct the evolutionary history of some components involved in auxin biology. In this review, we follow the evolutionary trajectory that allowed auxin to become the "giant" of plant biology by focusing on bryophytes and streptophyte algae. We consider auxin biosynthesis, transport, physiological, and molecular responses, as well as evidence supporting the role of auxin as a chemical messenger for communication within ecosystems. Finally, we emphasize that functional validation of predicted orthologs will shed light on the conserved properties of auxin biology among streptophytes.

Dopamine Inhibits Arabidopsis Growth through Increased Oxidative Stress and Auxin Activity

Like some bacterial species and all animals, plants synthesize dopamine and react to its exogenous applications. Despite dopamine’s widespread presence and activity in plants, its role in plant physiology is still poorly understood. Using targeted experimentation informed by the transcriptomic response to dopamine exposure, we identify three major effects of dopamine. First, we show that dopamine causes hypersensitivity to auxin indole-3-acetic acid by enhancing auxin activity. Second, we show that dopamine increases oxidative stress, which can be mitigated with glutathione. Third, we find that dopamine downregulates iron uptake mechanisms, leading to a decreased iron content—a response possibly aimed at reducing DA-induced oxidative stress. Finally, we show that dopamine-induced auxin sensitivity is downstream of glutathione biosynthesis, indicating that the auxin response is likely a consequence of DA-induced oxidative stress. Collectively, our results show that exogenous dopamine increases oxidative stress, which inhibits growth both directly and indirectly by promoting glutathione-biosynthesis-dependent auxin hypersensitivity.

Morphogenesis at the shoot meristem

Shoot apical meristems are populations of stem cells which initiate the aerial parts of higher plants. Work during the last decades has revealed a complex network of molecular regulators, which control both meristem maintenance and the production of different types of organs. The behavior of this network in time and space is defined by the local interactions between regulators and also involves hormonal regulation. In particular, auxin and cytokinin are intimately implicated in the coordination of gene expression patterns. To control growth patterns at the shoot meristem the individual components of the network influence directions and rates of cell growth. This requires interference with the mechanical properties of the cells. How this complex multiscale process, characterized by multiple feedbacks, is controlled remains largely an open question. Fortunately, genetics, live imaging, computational modelling and a number of other recently developed tools offer interesting albeit challenging perspectives.

Low-Speed Clinorotation of Brachypodium distachyon and Arabidopsis thaliana Seedlings Triggers Root Tip Curvatures That Are Reminiscent of Gravitropism

Clinostats are instruments that continuously rotate biological specimens along an axis, thereby averaging their orientation relative to gravity over time. Our previous experiments indicated that low-speed clinorotation may itself trigger directional root tip curvature. In this project, we have investigated the root curvature response to low-speed clinorotation using Arabidopsis thaliana and Brachypodium distachyon seedlings as models. We show that low-speed clinorotation triggers root tip curvature in which direction is dictated by gravitropism during the first half-turn of clinorotation. We also show that the angle of root tip curvature is modulated by the speed of clinorotation. Arabidopsis mutations affecting gravity susception (pgm) or gravity signal transduction (arg1, toc132) are shown to affect the root tip curvature response to low-speed clinorotation. Furthermore, low-speed vertical clinorotation triggers relocalization of the PIN3 auxin efflux facilitator to the lateral membrane of Arabidopsis root cap statocytes, and creates a lateral gradient of auxin across the root tip. Together, these observations support a role for gravitropism in modulating root curvature responses to clinorotation. Interestingly, distinct Brachypodium distachyon accessions display different abilities to develop root tip curvature responses to low-speed vertical clinorotation, suggesting the possibility of using genome-wide association studies to further investigate this process.

Genome-wide identification and expression analysis of AUX/LAX family genes in Chinese hickory (Carya cathayensis Sarg.) Under various abiotic stresses and grafting

Auxin is essential for regulating plant growth and development as well as the response of plants to abiotic stresses. AUX/LAX proteins are auxin influx transporters belonging to the amino acid permease family of proton-driven transporters, and are involved in the transport of indole-3-acetic acid (IAA). However, how AUX/LAX genes respond to abiotic stresses in Chinese hickory is less studied. For the first time identification, structural characteristics as well as gene expression analysis of the AUX/LAX gene family in Chinese hickory were conducted by using techniques of gene cloning and real-time fluorescent quantitative PCR. Eight CcAUX/LAXs were identified in Chinese hickory, all of which had the conserved structural characteristics of AUX/LAXs. CcAUX/LAXs were most closely related to their homologous proteins in Populus trichocarpa , which was in consistence with their common taxonomic character of woody trees. CcAUX/LAXs exhibited different expression profiles in different tissues, indicating their varying roles during growth and development. A number of light-, hormone-, and abiotic stress responsive cis-acting regulatory elements were detected on the promoters of CcAUX/LAX genes. CcAUX/LAX genes responded differently to drought and salt stress treatments to varying degrees. Furthermore, CcAUX/LAX genes exhibited complex expression changes during Chinese hickory grafting. These findings not only provide a valuable resource for further functional validation of CcAUX/LAXs, but also contribute to a better understanding of their potential regulatory functions during grafting and abiotic stress treatments in Chinese hickory.

Genome-Wide Analysis of the AAAP Gene Family in Populus and Functional Analysis of PsAAAP21 in Root Growth and Amino Acid Transport

The adventitious root (AR) is the basis for successful propagation by plant cuttings and tissue culture and is essential for maintaining the positive traits of a variety. Members of the amino acid/auxin permease (AAAP) gene family play indispensable roles in various plant metabolisms and have few studies on root growth and amino acid transport. In this study, with a systematic bioinformatics analysis of the Populus AAAP family, 83 PtrAAAPs were identified from Populus trichocarpa and grouped into 8 subfamilies. Subsequently, chromosomal distribution, genetic structure, cis-elements analysis, and expression pattern analysis of the AAAP family were performed and the potential gene AAAP21 regulating root development was screened by combining the results of RNA-Seq and QTL mapping. PsAAAP21 was proven as promoting root development by enhancing AR formation. Differentially expressed genes (DEGs) from RNA-seq results of overexpressing lines were enriched to multiple amino acid-related pathways, and the amino acid treatment to transgenic lines indicated that PsAAAP21 regulated amino acid transport, including tyrosine, methionine, and arginine. Analysis of the AAAP gene family provided a theoretical basis for uncovering the functions of AAAP genes. The identification of PsAAAP21 on root promotion and amino acid transport in Populus will help with breeding new woody plant species with strong rooting ability.

Glutathione Plays a Positive Role in the Proliferation of Pinus koraiensis Embryogenic Cells

In the large-scale breeding of conifers, cultivating embryogenic cells with good proliferative capacity is crucial in the process of somatic embryogenesis. In the same cultural environment, the proliferative capacity of different cell lines is significantly different. To reveal the regulatory mechanism of proliferation in woody plant cell lines with different proliferative potential, we used Korean pine cell lines with high proliferative potential 001#-001 (Fast) and low proliferative potential 001#-010 (Slow) for analysis. A total of 17 glutathione-related differentially expressed genes was identified between F and S cell lines. A total of 893 metabolites was obtained from the two cell lines in the metabolomic studies. A total of nine metabolites related to glutathione was significantly upregulated in the F cell line compared with the S cell line. The combined analyses revealed that intracellular glutathione might be the key positive regulator mediating the difference in proliferative capacity between F and S cell lines. The qRT-PCR assay validated 11 differentially expressed genes related to glutathione metabolism. Exogenous glutathione and its synthase inhibitor L-buthionine-sulfoximine treatment assay demonstrated the positive role of glutathione in the proliferation of Korean pine embryogenic cells.

AtHB40 modulates primary root length and gravitropism involving CYCLINB and auxin transporters

Gravitropism is a finely regulated tropistic response based on the plant perception of directional cues. Such perception allows them to direct shoot growth upwards, above ground, and root growth downwards, into the soil, anchoring the plant to acquire water and nutrients. Gravity sensing occurs in specialized cells and depends on auxin distribution, regulated by influx/efflux carriers. Here we report that AtHB40, encoding a transcription factor of the homeodomain-leucine zipper I family, was expressed in the columella and the root tip. Athb40 mutants exhibited longer primary roots. Enhanced primary root elongation was in agreement with a higher number of cells in the transition zone and the induction of CYCLINB transcript levels. Moreover, athb40 mutants and AtHB40 overexpressors displayed enhanced and delayed gravitropistic responses, respectively. These phenotypes were associated with altered auxin distribution and deregulated expression of the auxin transporters LAX2, LAX3, and PIN2. Accordingly, lax2 and lax3 mutants also showed an altered gravitropistic response, and LAX3 was identified as a direct target of AtHB40. Furthermore, AtHB40 is induced by AtHB53 when the latter is upregulated by auxin. Altogether, these results indicate that AtHB40 modulates cell division and auxin distribution in the root tip thus altering primary root length and gravitropism.

The unconventional prefoldin RPB5 interactor mediates the gravitropic response by modulating cytoskeleton organization and auxin transport in Arabidopsis

Gravity-induced root curvature involves the asymmetric distribution of the phytohormone auxin. This response depends on the concerted activities of the auxin transporters such as PIN-FORMED (PIN) proteins for auxin efflux and AUXIN RESISTANT 1 (AUX1) for auxin influx. However, how the auxin gradient is established remains elusive. Here we identified a new mutant with a short root, strong auxin distribution in the lateral root cap and an impaired gravitropic response. The causal gene encoded an Arabidopsis homolog of the human unconventional prefoldin RPB5 interactor (URI). AtURI interacted with prefoldin 2 (PFD2) and PFD6, two β-type PFD members that modulate actin and tubulin patterning in roots. The auxin reporter DR5_rev :GFP showed that asymmetric auxin redistribution after gravistimulation is disordered in aturi-1 root tips. Treatment with the endomembrane protein trafficking inhibitor brefeldin A indicated that recycling of the auxin transporter PIN2 is disrupted in aturi-1 roots as well as in pfd mutants. We propose that AtURI cooperates with PFDs to recycle PIN2 and modulate auxin distribution.

PIN and PILS family genes analyses in Chrysanthemum seticuspe reveal their potential functions in flower bud development and drought stress

Auxin affects almost all plant growth and developmental processes. The PIN-FORMED (PIN) and PIN-LIKES (PILS) family genes determine the direction and distribution gradient of auxin flow by polar localization on the cell membrane. However, there are no systematic studies on PIN and PILS family genes in chrysanthemum. Here, 18 PIN and 13 PILS genes were identified in Chrysanthemum seticuspe. The evolutionary relationships, physicochemical properties, conserved motifs, cis-acting elements, chromosome localization, collinearity, and expression characteristics of these genes were analyzed. CsPIN10a, CsPIN10b, and CsPIN10c are unique PIN genes in C. seticuspe. Expression pattern analysis showed that these genes had different tissue specificities, and the expression levels of CsPIN8, CsPINS1, CsPILS6, and CsPILS10 were linearly related to the developmental period of the flower buds. In situ hybridization assay showed that CsPIN1a, CsPIN1b, and CsPILS8 were expressed in floret primordia and petal tips, and CsPIN1a was specifically expressed in the middle of the bract primordia, which might regulate lateral expansion of the bracts. CsPIN and CsPILS family genes are also involved in drought stress responses. This study provides theoretical support for the cultivation of new varieties with attractive flower forms and high drought tolerance.

Fluorescent Auxin Analogs Report Two Auxin Binding Sites with Different Subcellular Distribution and Affinities: A Cue for Non-Transcriptional Auxin Signaling

The complexity of auxin signaling is partially due to multiple auxin receptors that trigger differential signaling. To obtain insight into the subcellular localization of auxin-binding sites, we used fluorescent auxin analogs that can undergo transport but do not deploy auxin signaling. Using fluorescent probes for different subcellular compartments, we can show that the fluorescent analog of 1-naphthaleneacetic acid (NAA) associates with the endoplasmic reticulum (ER) and tonoplast, while the fluorescent analog of indole acetic acid (IAA) binds to the ER. The binding of the fluorescent NAA analog to the ER can be outcompeted by unlabeled NAA, which allows us to estimate the affinity of NAA for this binding site to be around 1 μM. The non-transportable auxin 2,4-dichlorophenoxyacetic acid (2,4-D) interferes with the binding site for the fluorescent NAA analog at the tonoplast but not with the binding site for the fluorescent IAA analog at the ER. We integrate these data into a working model, where the tonoplast hosts a binding site with a high affinity for 2,4-D, while the ER hosts a binding site with high affinity for NAA. Thus, the differential subcellular localization of binding sites reflects the differential signaling in response to these artificial auxins.

Structures and mechanisms of the Arabidopsis auxin transporter PIN3

The PIN-FORMED (PIN) protein family of auxin transporters mediates the polar auxin transport and plays crucial roles in plant growth and development^1,2. Here we present cryo-EM structures of PIN3 from Arabidopsis thaliana (AtPIN3) in the apo state and in complex with its substrate indole-3-acetic acid (IAA) and the inhibitor N-1-naphthylphthalamic acid (NPA) at 2.6-3.0 Å resolution. AtPIN3 exists as a homodimer, with the transmembrane helices (TMs) 1, 2, and 7 in the scaffold domain involved in dimerization. The dimeric AtPIN3 forms a large, joint extracellular-facing cavity at the dimer interface while each subunit adopts an inward-facing conformation. The structural and functional analyses, along with computational studies, reveal the structural basis for the recognition of IAA and NPA and elucidate the molecular mechanism of NPA inhibition on the PIN-mediated auxin transport. The AtPIN3 structures support an elevator-like model for the transport of auxin, whereby the transport domains undergo up-down rigid-body motions and the dimerized scaffold domains remain static.

A feedback regulation between ARF7-mediated auxin signaling and auxin homeostasis involving MES17 affects plant gravitropism

Gravitropism is an essential adaptive response of land plants. Asymmetric auxin gradients across plant organs, interpreted by multiple auxin signaling components including AUXIN RESPONSE FACTOR7 (ARF7), trigger differential growth and bending response. However, how this fundamental process is strictly maintained in nature remains unclear. Here, we report that gravity stimulates the transcription of METHYL ESTERASE17 (MES17) along the lower side of the hypocotyl via ARF7-dependent auxin signaling. The asymmetric distribution of MES17, a methyltransferase that converts auxin from its inactive form methyl indole-3-acetic acid ester (MeIAA) to its biologically active form free-IAA, enhanced the gradient of active auxin across the hypocotyl, which in turn reversely amplified the asymmetric auxin responses and differential growth that shape gravitropic bending. Taken together, our findings reveal the novel role of MES17-mediated auxin homeostasis in gravitropic responses and identify an ARF7-triggered feedback mechanism that reinforces the asymmetric distribution of active auxin and strictly controls gravitropism in plants.

Systems approaches reveal that ABCB and PIN proteins mediate co-dependent auxin efflux

Members of the B family of membrane-bound ATP-binding cassette (ABC) transporters represent key components of the auxin efflux machinery in plants. Over the last two decades, experimental studies have shown that modifying ATP-binding cassette sub-family B (ABCB) expression affects auxin distribution and plant phenotypes. However, precisely how ABCB proteins transport auxin in conjunction with the more widely studied family of PIN-formed (PIN) auxin efflux transporters is unclear, and studies using heterologous systems have produced conflicting results. Here, we integrate ABCB localization data into a multicellular model of auxin transport in the Arabidopsis thaliana root tip to predict how ABCB-mediated auxin transport impacts organ-scale auxin distribution. We use our model to test five potential ABCB-PIN regulatory interactions, simulating the auxin dynamics for each interaction and quantitatively comparing the predictions with experimental images of the DII-VENUS auxin reporter in wild-type and abcb single and double loss-of-function mutants. Only specific ABCB-PIN regulatory interactions result in predictions that recreate the experimentally observed DII-VENUS distributions and long-distance auxin transport. Our results suggest that ABCBs enable auxin efflux independently of PINs; however, PIN-mediated auxin efflux is predominantly through a co-dependent efflux where co-localized with ABCBs.

Characterization of a Novel Creeping Tartary Buckwheat (Fagopyrum tataricum) Mutant lazy1

Gravity is known as an important environmental factor involved in the regulation of plant architecture. To identify genes related to the gravitropism of Tartary buckwheat, a creeping line was obtained and designated as lazy1 from the mutant bank by ⁶⁰Co-γ ray radiation. Genetic analysis indicated that the creeping phenotype of lazy1 was attributed to a single recessive locus. As revealed by the horizontal and inverted suspension tests, lazy1 was completely lacking in shoot negative gravitropism. The creeping growth of lazy1 occurred at the early seedling stage, which could not be recovered by exogenous heteroauxin, hormodin, α-rhodofix, or gibberellin. Different from the well-organized and equivalent cell elongation of wild type (WT), lazy1 exhibited dilated, distorted, and abnormally arranged cells in the bending stem. However, no statistical difference of indole-3-acetic acid (IAA) levels was found between the far- and near-ground bending sides in lazy1, which suggests that the asymmetric cell elongation of lazy1 was not induced by auxin gradient. Whereas, lazy1 showed up-expressed gibberellin-regulated genes by quantitative real-time PCR (qRT-PCR) as well as significantly higher levels of gibberellin, suggesting that gibberellin might be partly involved in the regulation of creeping growth in lazy1. RNA sequencing (RNA-seq) identified a number of differentially expressed genes (DEGs) related to gravitropism at stages I (before bending), II (bending), and III (after bending) between WT and lazy1. Venn diagram indicated that only Pectate lyase 5 was down-expressed at stages I [Log₂ fold change (Log₂FC): -3.20], II (Log₂FC: -4.97), and III (Log₂FC: -1.23) in lazy1, compared with WT. Gene sequencing revealed that a fragment deletion occurred in the coding region of Pectate lyase 5, which induced the destruction of a pbH domain in Pectate lyase 5 of lazy1. qRT-PCR indicated that Pectate lyase 5 was extremely down-expressed in lazy1 at stage II (0.02-fold of WT). Meanwhile, lazy1 showed the affected expression of lignin- and cellulose-related genes and cumulatively abnormal levels of pectin, lignin, and cellulose. These results demonstrate the possibility that Pectate lyase 5 functions as the key gene that could mediate primary cell wall metabolism and get involved in the asymmetric cell elongation regulation of lazy1.

The role of AUX1 during lateral root development in the domestication of the model C4 grass Setaria italica

C4 photosynthesis increases the efficiency of carbon fixation by spatially separating high concentrations of molecular oxygen from Rubisco. The specialized leaf anatomy required for this separation evolved independently many times. The morphology of C4 root systems is also distinctive and adapted to support high rates of photosynthesis; however, little is known about the molecular mechanisms that have driven the evolution of C4 root system architecture. Using a mutant screen in the C4 model plant Setaria italica, we identify Siaux1-1 and Siaux1-2 as root system architecture mutants. Unlike in S. viridis, AUX1 promotes lateral root development in S. italica. A cell by cell analysis of the Siaux1-1 root apical meristem revealed changes in the distribution of cell volumes in all cell layers and a dependence of the frequency of protophloem and protoxylem strands on SiAUX1. We explore the molecular basis of the role of SiAUX1 in seedling development using an RNAseq analysis of wild-type and Siaux1-1 plants and present novel targets for SiAUX1-dependent gene regulation. Using a selection sweep and haplotype analysis of SiAUX1, we show that Hap-2412TT in the promoter region of SiAUX1 is an allele which is associated with lateral root number and has been strongly selected for during Setaria domestication.

Cytokinin promotes growth cessation in the Arabidopsis root

The Arabidopsis root offers good opportunities to investigate how regulated cellular growth shapes different tissues and organs, a key question in developmental biology. Along the root's longitudinal axis, cells sequentially occupy different developmental states. Proliferative meristematic cells give rise to differentiating cells, which rapidly elongate in the elongation zone, then mature and stop growing in the differentiation zone. The phytohormone cytokinin contributes to this zonation by positioning the boundary between the meristem and the elongation zone, called the transition zone. However, the cellular growth profile underlying root zonation is not well understood, and the cellular mechanisms that mediate growth cessation remain unclear. By using time-lapse imaging, genetics, and computational analysis, we analyze the effect of cytokinin on root zonation and cellular growth. We found that cytokinin promotes growth cessation in the distal (shootward) elongation zone in conjunction with accelerating the transition from elongation to differentiation. We estimated cell-wall stiffness by using osmotic treatment experiments and found that cytokinin-mediated growth cessation is associated with cell-wall stiffening and requires the action of an auxin influx carrier, AUX1. Our measurement of growth and cell-wall mechanical properties at a cellular resolution reveal mechanisms via which cytokinin influences cell behavior to shape tissue patterns.

Insights into Factors Controlling Adventitious Root Formation in Apples

Adventitious root (AR) formation is required for the vegetative propagation of economically important horticultural crops, such as apples. Asexual propagation is commonly utilized for breeding programs because of its short life cycle, true-to-typeness, and high efficiency. The lack of AR formation from stem segments is a barrier to segment survival. Therefore, understanding the AR regulatory mechanisms is vital for the prolonged and effective use of biological resources. Several studies have been undertaken to comprehend the molecular and physiological control of AR, which has greatly extended our knowledge regarding AR formation in apples and other crops. Auxin, a master controller of AR formation, is widely used for inducing AR formation in stem cutting. At the same time, cytokinins (CKs) are important for cell division and molecular reprograming, and other hormones, sugars, and nutrients interact with auxin to control excision-induced AR formation. In this review, we discuss the present understandings of ARs’ formation from physiological and molecular aspects and highlight the immediate advancements made in identifying underlying mechanisms involved in the regulation of ARs. Despite the progress made in the previous decades, many concerns about excision-induced AR formation remain unanswered. These focus on the specific functions and interactions of numerous hormonal, molecular, and metabolic components and the overall framework of the entire shoot cutting in a demanding environment.

The volatile cedrene from Trichoderma guizhouense modulates Arabidopsis root development through auxin transport and signalling

Rhizosphere microorganisms interact with plant roots by producing chemical signals that regulate root development. However, the distinct bioactive compounds and signal transduction pathways remain to be identified. Here, we showed that sesquiterpenes are the main volatile compounds produced by plant-beneficial Trichoderma guizhouense NJAU4742. Inhibition of sesquiterpene biosynthesis eliminated the promoting effect of this strain on root growth, indicating its involvement in plant-fungus cross-kingdom signalling. Sesquiterpene component analysis identified cedrene, a highly abundant sesquiterpene in strain NJAU4742, to stimulate plant growth and root development. Genetic analysis and auxin transport inhibition showed that the TIR1 and AFB2 auxin receptors, IAA14 auxin-responsive protein, and ARF7 and ARF19 transcription factors affected the response of lateral roots to cedrene. Moreover, the AUX1 auxin influx carrier and PIN2 efflux carrier were also found to be indispensable for cedrene-induced lateral root formation. Confocal imaging showed that cedrene affected the expression of pPIN2:PIN2:GFP and pPIN3:PIN3:GFP, which might be related to the effect of cedrene on root morphology. These results suggested that a novel sesquiterpene molecule from plant-beneficial T. guizhouense regulates plant root development through the transport and signalling of auxin.

Auxin Transporters-A Biochemical View

From embryogenesis to fruit formation, almost every aspect of plant development and differentiation is controlled by the cellular accumulation or depletion of auxin from cells and tissues. The respective auxin maxima and minima are generated by cell-to-cell auxin transport via transporter proteins. Differential auxin accumulation as a result of such transport processes dynamically regulates auxin distribution during differentiation. In this review, we introduce all auxin transporter (families) identified to date and discuss the knowledge on prominent family members, namely, the PIN-FORMED exporters, ATP-binding cassette B (ABCB)-type transporters, and AUX1/LAX importers. We then concentrate on the biochemical features of these transporters and their regulation by posttranslational modifications and interactors.

OsRLR4 binds to the OsAUX1 promoter to negatively regulate primary root development in rice

Root architecture is one of the most important agronomic traits that determines rice crop yield. The primary root (PR) absorbs mineral nutrients and provides mechanical support; however, the molecular mechanisms of PR elongation remain unclear in rice. Here, the two loss-of-function T-DNA insertion mutants of root length regulator 4 (OsRLR4), osrlr4-1 and osrlr4-2 with longer PR, and three OsRLR4 overexpression lines, OE-OsRLR4-1/-2/-3 with shorter PR compared to the wild type/Hwayoung (WT/HY), were identified. OsRLR4 is one of five members of the PRAF subfamily of the regulator chromosome condensation 1 (RCC1) family. Phylogenetic analysis of OsRLR4 from wild and cultivated rice indicated that it is under selective sweeps, suggesting its potential role in domestication. OsRLR4 controls PR development by regulating auxin accumulation in the PR tip and thus the root apical meristem activity. A series of biochemical and genetic analyses demonstrated that OsRLR4 functions directly upstream of the auxin transporter OsAUX1. Moreover, OsRLR4 interacts with the TRITHORAX-like protein OsTrx1 to promote H3K4me3 deposition at the OsAUX1 promoter, thus altering its transcription level. This work provides insight into the cooperation of auxin and epigenetic modifications in regulating root architecture and provides a genetic resource for plant architecture breeding.

The Virtual Root : Mathematical Modeling of Auxin Transport in the Arabidopsis Root Tip Using the Open-Source Software SimuPlant

Hormone signals like auxin play a critical role controlling plant growth and development. Determining the mechanisms that regulate auxin distribution in cells and tissues is a vital step in understanding this hormone's role during plant development. Recent mathematical models have enabled us to understand the essential role that auxin influx and efflux carriers play in auxin transport in the Arabidopsis root tip (Band et al., Plant Cell 26(3):862-875, 2014; Grieneisen et al., Nature 449(7165):1008-1013, 2007; van den Berg et al., Development 143(18):3350-3362, 2016). In this chapter, we describe SimuPlant: The Virtual Root (SimuPlant, University of Nottingham. https://www.simuplant.org/ . Accessed 20 Sept 2019); an open source software suite, built using the OpenAlea (Pradal et al., Funct Plant Biol 35(10):751-760, 2008) framework, that is designed to simulate vertex-based models in real plant tissue geometries. We provide guidance on how to install SimuPlant, run 2D auxin transport models in the Arabidopsis root tip, manipulate parameters, and visualize model outputs.SimuPlant features a graphical user interface (GUI) designed to allow users with no programming experience to simulate auxin dynamics within the Arabidopsis root tip. Within the user interface, users of SimuPlant can select from a range of model assumptions and can choose to manipulate model and simulation parameter values. Users can then investigate how their choices affect the predicted distribution of auxin in the Arabidopsis root tip. The results of the model simulations are shown visually within the root geometry and can be exported and saved as PNG image files.

ACORBA: Automated workflow to measure Arabidopsis thaliana root tip angle dynamics

The ability of plants to sense and orient their root growth towards gravity is studied in many laboratories. It is known that manual analysis of image data is subjected to human bias. Several semi-automated tools are available for analysing images from flatbed scanners, but there is no solution to automatically measure root bending angle over time for vertical-stage microscopy images. To address these problems, we developed ACORBA, which is an automated software that can measure root bending angle over time from vertical-stage microscope and flatbed scanner images. ACORBA also has a semi-automated mode for camera or stereomicroscope images. It represents a flexible approach based on both traditional image processing and deep machine learning segmentation to measure root angle progression over time. As the software is automated, it limits human interactions and is reproducible. ACORBA will support the plant biologist community by reducing labour and increasing reproducibility of image analysis of root gravitropism.

Promoter profiling of Arabidopsis amino acid transporters: clues for improving crops

The review describes the importance of amino acid transporters in plant growth, development, stress tolerance, and productivity. The promoter analysis provides valuable insights into their functionality leading to agricultural benefits. Arabidopsis thaliana genome is speculated to possess more than 100 amino acid transporter genes. This large number suggests the functional significance of amino acid transporters in plant growth and development. The current article summarizes the substrate specificity, cellular localization, tissue-specific expression, and expression of the amino acid transporter genes in response to environmental cues. However, till date functionality of a majority of amino acid transporter genes in plant development and stress tolerance is unexplored. Considering, that gene expression is mainly regulated by the regulatory motifs localized in their promoter regions at the transcriptional levels. The promoter regions ( ~ 1-kbp) of these amino acid transporter genes were analysed for the presence of cis-regulatory motifs responsive to developmental and external cues. This analysis can help predict the functionality of known and unexplored amino acid transporters in different tissues, organs, and various growth and development stages and responses to external stimuli. Furthermore, based on the promoter analysis and utilizing the microarray expression data we have attempted to identify plausible candidates (listed below) that might be targeted for agricultural benefits.

Genome-Wide Analysis of AAT Genes and Their Expression Profiling during Fiber Development in Cotton

Amino acid transporters (AATs) are a kind of membrane proteins that mediate the transport of amino acids across cell membranes in higher plants. The AAT proteins are involved in regulating plant cell growth and various developmental processes. However, the biological function of this gene family in cotton fiber development is not clear. In this study, 190, 190, 101, and 94 full-length AAT genes were identified from Gossypiumhirsutum, G. barbadense, G. arboreum, and G. raimondii. A total of 575 AAT genes from the four cotton species were divided into two subfamilies and 12 clades based on phylogenetic analysis. The AAT genes in the four cotton species were distributed on all the chromosomes. All GhAAT genes contain multiple exons, and each GhAAT protein has multiple conserved motifs. Transcriptional profiling and RT qPCR analysis showed that four GhATT genes tend to express specifically at the fiber initiation stage. Eight genes tend to express specifically at the fiber elongation and maturity stage, and four genes tend to express specifically at the fiber initiation and elongation stages. Our results provide a solid basis for further elucidating the biological function of AAT genes related to cotton fiber development and offer valuable genetic resources for crop improvement in the future.

Casting the Net-Connecting Auxin Signaling to the Plant Genome

Auxin represents one of the most potent and most versatile hormonal signals in the plant kingdom. Built on a simple core of only a few dedicated components, the auxin signaling system plays important roles for diverse aspects of plant development, physiology, and defense. Key to the diversity of context-dependent functional outputs generated by cells in response to this small molecule are gene duplication events and sub-functionalization of signaling components on the one hand, and a deep embedding of the auxin signaling system into complex regulatory networks on the other hand. Together, these evolutionary innovations provide the mechanisms to allow each cell to display a highly specific auxin response that suits its individual requirements. In this review, we discuss the regulatory networks connecting auxin with a large number of diverse pathways at all relevant levels of the signaling system ranging from biosynthesis to transcriptional response.

The Glycine-Rich Domain Protein GRDP2 Regulates Ovule Development via the Auxin Pathway in Arabidopsis

The glycine-rich domain proteins (GRDP) have been functionally implicated in the cell wall structure, biotic, and abiotic stress responses. However, little is known about GRDP genes in female gametophyte development of Arabidopsis. This study shows that GRDP2, a GRDP, plays a crucial role in female gametophyte development. In GRDP2 overexpression lines, grdp2-3, the embryo sacs were arrested at FG1 and no nucleus stages. Furthermore, callose staining shows that cell plate formation during megasporogenesis is disturbed in grdp2-3. In contrast, the pollen development is not affected in grdp2-3. The expression patterns of auxin-specific marker lines in female gametophytes showed that the auxin distribution and transport were significantly changed during megagametogenesis in grdp2-3. In addition, compared with the membrane-localized pattern of PIN1, PIN2, and PIN7 in WT, the signals were detected in the cytoplasm in grdp2-3. Together, our data suggest that GRDP2 plays an essential role in auxin-mediated female gametophyte development.

A novel miR167a-OsARF6-OsAUX3 module regulates grain length and weight in rice

Grain size is one of the most important factors that control rice yield, as it is associated with grain weight (GW). To date, dozens of rice genes that regulate grain size have been isolated; however, the regulatory mechanism underlying GW control is not fully understood. Here, the quantitative trait locus qGL5 for grain length (GL) and GW was identified in recombinant inbred lines of 9311 and Nipponbare (NPB) and fine mapped to a candidate gene, OsAUX3. Sequence variations between 9311 and NPB in the OsAUX3 promoter and loss of function of OsAUX3 led to higher GL and GW. RNA sequencing, gene expression quantification, dual-luciferase reporter assays, chromatin immunoprecipitation-quantitative PCR, and yeast one-hybrid assays demonstrated that OsARF6 is an upstream transcription factor regulating the expression of OsAUX3. OsARF6 binds directly to the auxin response elements of the OsAUX3 promoter, covering a single-nucleotide polymorphism site between 9311 and NPB/Dongjin/Hwayoung, and thereby controls GL by altering longitudinal expansion and auxin distribution/content in glume cells. Furthermore, we showed that miR167a positively regulate GL and GW by directing OsARF6 mRNA silencing. Taken together, our study reveals that a novel miR167a-OsARF6-OsAUX3 module regulates GL and GW in rice, providing a potential target for the improvement of rice yield.