Special Issue "Advances in Auxin Research"

A special issue of Plants (ISSN 2223-7747). This special issue belongs to the section "Plant Physiology and Metabolism".

Deadline for manuscript submissions: closed (1 December 2020).

Special Issue Editors

Dr. Helene Robert Boisivon
Website
Guest Editor
Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology (CEITEC), Masaryk University, Kamenice 5, Brno, CZ-625 00, Brno, Czech Republic
Interests: plant development; seed development; auxin production; abiotic stress
Dr. Marta Zwiewka
Website
Guest Editor
Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology (CEITEC), Masaryk University, Kamenice 5, Brno, CZ-625 00, Brno, Czech Republic
Interests: vesicular trafficking; auxin signaling; cellular stress response

Special Issue Information

Dear Colleagues,

Phytohormones are endogenous molecules occurring naturally in plants at minute concentrations. They act as signalling compounds that promote and influence plant development and physiology. Auxin has been identified as a plant growth hormone for its ability to stimulate differential growth in response to gravity or light cues. It is involved in a wide variety of biological mechanisms. It includes basic cellular processes (endocytosis, cell polarity, and cell cycle control) for localized responses (cell elongation and differential growth). Therefore, auxin regulates macroscopic phenomena (embryogenesis, tissue patterning, and de novo formation of organs).

The effect of auxin on plant growth and development depends primarily on its amount and distribution in organs and tissues. This regulation is implemented on at least four functional levels: hormone biosynthesis; its metabolism, especially the formation and hydrolysis of conjugates; its active or passive transport; and the perception and processing of auxin signalling by nuclear protein receptors.

The cellular and tissular sensitivities to the auxin signals, as well as extraordinary self-organizing and self-regulating properties of auxin biology, are further translated to the plant phenotypes and give important impulses for flexible plant development.

Even though the history of auxin research reaches back more than a hundred years, we are still far from having a comprehensive understanding of how auxin governs a wide range of plant responses. Therefore, with this Special Issue we want to give you the opportunity to contribute research articles or reviews concerning any of the auxin-related aspects mentioned above.

Dr. Helene Robert Boisivon
Dr. Marta Zwiewka
Guest Editors

Manuscript Submission Information

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Keywords

  • auxin metabolism
  • auxin signalling
  • polar auxin transport
  • auxin biosynthesis

Published Papers (9 papers)

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Research

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Open AccessArticle
Dissecting Hierarchies between Light, Sugar and Auxin Action Underpinning Root and Root Hair Growth
Plants 2021, 10(1), 111; https://doi.org/10.3390/plants10010111 - 07 Jan 2021
Abstract
Plant roots are very plastic and can adjust their tissue organization and cell appearance during abiotic stress responses. Previous studies showed that direct root illumination and sugar supplementation mask root growth phenotypes and traits. Sugar and light signaling where further connected to changes [...] Read more.
Plant roots are very plastic and can adjust their tissue organization and cell appearance during abiotic stress responses. Previous studies showed that direct root illumination and sugar supplementation mask root growth phenotypes and traits. Sugar and light signaling where further connected to changes in auxin biosynthesis and distribution along the root. Auxin signaling underpins almost all processes involved in the establishment of root traits, including total root length, gravitropic growth, root hair initiation and elongation. Root hair plasticity allows maximized nutrient uptake and therefore plant productivity, and root hair priming and elongation require proper auxin availability. In the presence of sucrose in the growth medium, root hair emergence is partially rescued, but the full potential of root hair elongation is lost. With our work we describe a combinatory study showing to which extent light and sucrose are antagonistically influencing root length, but additively affecting root hair emergence and elongation. Furthermore, we investigated the impact of the loss of PIN-FORMED2, an auxin efflux carrier mediating shootward auxin transporter, on the establishment of root traits in combination with all growth conditions. Full article
(This article belongs to the Special Issue Advances in Auxin Research)
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Open AccessArticle
Expression Analysis of Key Auxin Biosynthesis, Transport, and Metabolism Genes of Betula pendula with Special Emphasis on Figured Wood Formation in Karelian Birch
Plants 2020, 9(11), 1406; https://doi.org/10.3390/plants9111406 - 22 Oct 2020
Abstract
Auxin status in woody plants is believed to be a critical factor for the quantity and quality of the wood formed. It has been previously demonstrated that figured wood formation in Karelian birch (Betula pendula Roth var. carelica (Merckl.) Hämet-Ahti) is associated [...] Read more.
Auxin status in woody plants is believed to be a critical factor for the quantity and quality of the wood formed. It has been previously demonstrated that figured wood formation in Karelian birch (Betula pendula Roth var. carelica (Merckl.) Hämet-Ahti) is associated with a reduced auxin level and elevated sugar content in the differentiating xylem, but the molecular mechanisms of the abnormal xylogenesis remained largely unclear. We have identified genes involved in auxin biosynthesis (Yucca), polar auxin transport (PIN) and the conjugation of auxin with amino acids (GH3) and UDP-glucose (UGT84B1) in the B. pendula genome, and analysed their expression in trunk tissues of trees differing in wood structure. Almost all the investigated genes were overexpressed in Karelian birch trunks. Although Yucca genes were overexpressed, trunk tissues in areas developing figured grain had traits of an auxin-deficient phenotype. Overexpression of GH3s and UGT84B1 appears to have a greater effect on figured wood formation. Analysis of promoters of the differentially expressed genes revealed a large number of binding sites with various transcription factors associated with auxin and sugar signalling. These data agree with the hypothesis that anomalous figured wood formation in Karelian birch may be associated with the sugar induction of auxin conjugation. Full article
(This article belongs to the Special Issue Advances in Auxin Research)
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Open AccessArticle
Genome-Wide Analysis of the PIN Auxin Efflux Carrier Gene Family in Coffee
Plants 2020, 9(9), 1061; https://doi.org/10.3390/plants9091061 - 19 Aug 2020
Abstract
Coffee is one of the most popular beverages around the world, which is mainly produced from the allopolyploid Coffea arabica. The genomes of C. arabica and its two ancestors C. canephora and C. eugenioides have been released due to the development of [...] Read more.
Coffee is one of the most popular beverages around the world, which is mainly produced from the allopolyploid Coffea arabica. The genomes of C. arabica and its two ancestors C. canephora and C. eugenioides have been released due to the development of next generation sequencing. However, few studies on C. arabica are related to the PIN-FORMED (PIN) auxin efflux transporter despite its importance in auxin-mediated plant growth and development. In the present study, we conducted a genome-wide analysis of the PIN gene family in the three coffee species. Totals of 17, 9 and 10 of the PIN members were characterized in C. Arabica, C. canephora and C. eugenioides, respectively. Phylogenetic analysis revealed gene loss of PIN1 and PIN2 homologs in C. arabica, as well as gene duplication of PIN5 homologs during the fractionation process after tetraploidy. Furthermore, we conducted expression analysis of PIN genes in C. arabica by in silico and qRT-PCR. The results revealed the existence of gene expression dominance in allopolyploid coffee and illustrated several PIN candidates in regulating auxin transport and homeostasis under leaf rust fungus inoculation and the tissue-specific expression pattern of C. arabica. Together, this study provides the basis and guideline for future functional characterization of the PIN gene family. Full article
(This article belongs to the Special Issue Advances in Auxin Research)
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Open AccessFeature PaperArticle
In Vivo Reporters for Visualizing Alternative Splicing of Hormonal Genes
Plants 2020, 9(7), 868; https://doi.org/10.3390/plants9070868 - 08 Jul 2020
Abstract
Rapid progress in plant molecular biology in recent years has uncovered the main players in hormonal pathways and characterized transcriptomic networks associated with hormonal response. However, the role of RNA processing, in particular alternative splicing (AS), remains largely unexplored. Here, using example genes [...] Read more.
Rapid progress in plant molecular biology in recent years has uncovered the main players in hormonal pathways and characterized transcriptomic networks associated with hormonal response. However, the role of RNA processing, in particular alternative splicing (AS), remains largely unexplored. Here, using example genes involved in cytokinin signaling, brassinosteroid synthesis and auxin transport, we present a set of reporters devised to visualize their AS events in vivo. These reporters show a differential tissue-specific expression of certain transcripts and reveal that expression of some of the them can be changed by the application of the exogenous hormone. Finally, based on the characterized AS event of the PIN7 auxin efflux carrier, we designed a system that allows a rapid genetic screening for the factors upstream of this AS event. Our innovative toolset can be therefore highly useful for exploring novel regulatory nodes of hormonal pathways and potentially helpful for plant researchers focusing on developmental aspects of AS. Full article
(This article belongs to the Special Issue Advances in Auxin Research)
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Open AccessArticle
Effect of Ammonia and Indole-3-acetic Acid Producing Endophytic Klebsiella pneumoniae YNA12 as a Bio-Herbicide for Weed Inhibition: Special Reference with Evening Primroses
Plants 2020, 9(6), 761; https://doi.org/10.3390/plants9060761 - 18 Jun 2020
Abstract
Information on the use of endophytic bacteria as a bio-herbicide for the management of weed control in agricultural fields is limited. The current study aimed to isolate endophytic bacteria from evening primroses and to screen them for their bio-herbicidal activity. Two isolated endophytic [...] Read more.
Information on the use of endophytic bacteria as a bio-herbicide for the management of weed control in agricultural fields is limited. The current study aimed to isolate endophytic bacteria from evening primroses and to screen them for their bio-herbicidal activity. Two isolated endophytic bacteria (Pantoea dispersa YNA11 and Klebsiella pneumoniae YNA12) were initially screened for citrate utilization and for indole-3-acetic acid (IAA) and catalase production. The preliminary biochemical assessment showed YNA12 as a positive strain. Ammonia, catalase, and IAA in its culture filtrate were quantified. Gas Chromatography/Mass Spectroscopy- Selective Ion Monitoring (GC/MS-SIM) analysis revealed the production of IAA by YNA12 in a time-dependent manner. YNA12 also exhibited significant ammonia-producing potential and catalase activity against hydrogen peroxide. The YNA12 culture filtrate significantly inhibited the germination rate of evening primrose seeds, resulting in a marked reduction in seedling length and biomass compared with those of the control seeds. Moreover, the culture filtrate of YNA12 significantly accelerated the endogenous abscisic acid (ABA) production and catalase activity of evening primrose seedlings. Macronutrient regulation was adversely affected in the seedlings exposed to the culture filtrate of YNA12, leading to inhibition of seed germination. The current results suggest that endophytic YNA12 may be used as a potent bio-herbicidal agent for controlling weed growth and development. Full article
(This article belongs to the Special Issue Advances in Auxin Research)
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Open AccessArticle
Characterization of the Auxin Efflux Transporter PIN Proteins in Pear
Plants 2020, 9(3), 349; https://doi.org/10.3390/plants9030349 - 10 Mar 2020
Cited by 2
Abstract
PIN-FORMED (PIN) encodes a key auxin polar transport family that plays a crucial role in the outward transport of auxin and several growth and development processes, including dwarfing trees. We identified a dwarfing pear rootstock ‘OHF51’ (Pyrus communis), which limits the [...] Read more.
PIN-FORMED (PIN) encodes a key auxin polar transport family that plays a crucial role in the outward transport of auxin and several growth and development processes, including dwarfing trees. We identified a dwarfing pear rootstock ‘OHF51’ (Pyrus communis), which limits the growth vigor of the ‘Xueqing’ (Pyrus bretschneideri × Pyrus pyrifolia) scion, and isolated 14 putative PbPINs from the pear Pyrus bretschneideri. The phylogenic relationships, structure, promoter regions, and expression patterns were analyzed. PbPINs were classified into two main groups based on the protein domain structure and categorized into three major groups using the neighbor-joining algorithm. Promoter analysis demonstrated that PbPINs might be closely related to plant growth and development. Through quantitative real-time PCR (qRT-PCR) analysis, we found that the expression patterns of 14 PbPINs varied upon exposure to different organs in dwarfing and vigorous stocks, ‘OHF51’ and ‘QN101’ (Pyrus betulifolia), indicating that they might play varying roles in different tissues and participated in the regulation of growth vigor. These results provide fundamental insights into the characteristics and evolution of the PINs family, as well as the possible relationship between dwarfing ability and auxin polar transport. Full article
(This article belongs to the Special Issue Advances in Auxin Research)
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Review

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Open AccessReview
The TOR–Auxin Connection Upstream of Root Hair Growth
Plants 2021, 10(1), 150; https://doi.org/10.3390/plants10010150 - 13 Jan 2021
Abstract
Plant growth and productivity are orchestrated by a network of signaling cascades involved in balancing responses to perceived environmental changes with resource availability. Vascular plants are divided into the shoot, an aboveground organ where sugar is synthesized, and the underground located root. Continuous [...] Read more.
Plant growth and productivity are orchestrated by a network of signaling cascades involved in balancing responses to perceived environmental changes with resource availability. Vascular plants are divided into the shoot, an aboveground organ where sugar is synthesized, and the underground located root. Continuous growth requires the generation of energy in the form of carbohydrates in the leaves upon photosynthesis and uptake of nutrients and water through root hairs. Root hair outgrowth depends on the overall condition of the plant and its energy level must be high enough to maintain root growth. TARGET OF RAPAMYCIN (TOR)-mediated signaling cascades serve as a hub to evaluate which resources are needed to respond to external stimuli and which are available to maintain proper plant adaptation. Root hair growth further requires appropriate distribution of the phytohormone auxin, which primes root hair cell fate and triggers root hair elongation. Auxin is transported in an active, directed manner by a plasma membrane located carrier. The auxin efflux carrier PIN-FORMED 2 is necessary to transport auxin to root hair cells, followed by subcellular rearrangements involved in root hair outgrowth. This review presents an overview of events upstream and downstream of PIN2 action, which are involved in root hair growth control. Full article
(This article belongs to the Special Issue Advances in Auxin Research)
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Open AccessReview
ER-Localized PIN Carriers: Regulators of Intracellular Auxin Homeostasis
Plants 2020, 9(11), 1527; https://doi.org/10.3390/plants9111527 - 10 Nov 2020
Abstract
The proper distribution of the hormone auxin is essential for plant development. It is channeled by auxin efflux carriers of the PIN family, typically asymmetrically located on the plasma membrane (PM). Several studies demonstrated that some PIN transporters are also located at the [...] Read more.
The proper distribution of the hormone auxin is essential for plant development. It is channeled by auxin efflux carriers of the PIN family, typically asymmetrically located on the plasma membrane (PM). Several studies demonstrated that some PIN transporters are also located at the endoplasmic reticulum (ER). From the PM-PINs, they differ in a shorter internal hydrophilic loop, which carries the most important structural features required for their subcellular localization, but their biological role is otherwise relatively poorly known. We discuss how ER-PINs take part in maintaining intracellular auxin homeostasis, possibly by modulating the internal levels of IAA; it seems that the exact identity of the metabolites downstream of ER-PINs is not entirely clear as well. We further review the current knowledge about their predicted structure, evolution and localization. Finally, we also summarize their role in plant development. Full article
(This article belongs to the Special Issue Advances in Auxin Research)
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Open AccessReview
Photoreceptors Regulate Plant Developmental Plasticity through Auxin
Plants 2020, 9(8), 940; https://doi.org/10.3390/plants9080940 - 24 Jul 2020
Cited by 1
Abstract
Light absorption by plants changes the composition of light inside vegetation. Blue (B) and red (R) light are used for photosynthesis whereas far-red (FR) and green light are reflected. A combination of UV-B, blue and R:FR-responsive photoreceptors collectively measures the light and temperature [...] Read more.
Light absorption by plants changes the composition of light inside vegetation. Blue (B) and red (R) light are used for photosynthesis whereas far-red (FR) and green light are reflected. A combination of UV-B, blue and R:FR-responsive photoreceptors collectively measures the light and temperature environment and adjusts plant development accordingly. This developmental plasticity to photoreceptor signals is largely regulated through the phytohormone auxin. The phytochrome, cryptochrome and UV Resistance Locus 8 (UVR8) photoreceptors are inactivated in shade and/or elevated temperature, which releases their repression of Phytochrome Interacting Factor (PIF) transcription factors. Active PIFs stimulate auxin synthesis and reinforce auxin signalling responses through direct interaction with Auxin Response Factors (ARFs). It was recently discovered that shade-induced hypocotyl elongation and petiole hyponasty depend on long-distance auxin transport towards target cells from the cotyledon and leaf tip, respectively. Other responses, such as phototropic bending, are regulated by auxin transport and signalling across only a few cell layers. In addition, photoreceptors can directly interact with components in the auxin signalling pathway, such as Auxin/Indole Acetic Acids (AUX/IAAs) and ARFs. Here we will discuss the complex interactions between photoreceptor and auxin signalling, addressing both mechanisms and consequences of these highly interconnected pathways. Full article
(This article belongs to the Special Issue Advances in Auxin Research)
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