Role Of Auxin Research Articles

Role of auxin and gibberellin under low light in enhancing saffron corm starch degradation during sprouting

The mechanisms by which low light accelerates starch macromolecules degradation by auxin and gibberellin (GA) in geophytes during sprouting remain largely unknown. This study investigated these mechanisms in saffron, grown under low light (50 μmol m−2 s−1) and optimal light (200 μmol m−2 s−1) during the sprouting phase. Low light reduced starch concentration in corms by 34.0 % and increased significantly sucrose levels in corms, leaves, and leaf sheaths by 19.2 %, 9.8 %, and 134.5 %, respectively. This was associated with a 33.3 % increase in GA3 level and enhanced auxin signaling. Leaves synthesized IAA under low light, which was transported to the corms to promote GA synthesis, facilitating starch degradation through a 228.7 % increase in amylase activity. Exogenous applications of GA and IAA, as well as the use of their synthesis or transport inhibitors, confirmed the synergistic role of these phytohormones in starch metabolism. The unigenes associated with GA biosynthesis and auxin signaling were upregulated under low light, highlighting the IAA-GA module role in starch degradation. Moreover, increased respiration rate and invertase activity, crucial for ATP biosynthesis and the tricarboxylic acid cycle, were consistent with the upregulation of related unigenes, suggesting that auxin signaling accelerates starch degradation by promoting energy metabolism. Upregulated of auxin signaling (CsSAUR32) and starch metabolism (CsSnRK1) genes under low light suggests that auxin directly regulate starch degradation in saffron corms. This study elucidates that low light modulates auxin and GA interactions to accelerate starch degradation in saffron corms during sprouting, offering insights for optimizing agricultural practices under suboptimal light conditions.

Cytokinin signaling is involved in root hair elongation in response to phosphate starvation

ABSTRACT Root hair, single-celled tubular structures originating from the epidermis, plays a vital role in the uptake of nutrients from the soil by increasing the root surface area. Therefore, optimizing root hair growth is crucial for plants to survive in fluctuating environments. Root hair length is determined by the action of various plant hormones, among which the roles of auxin and ethylene have been extensively studied. However, evidence for the involvement of cytokinins has remained elusive. We recently reported that the cytokinin-activated B-type response regulators, ARABIDOPSIS RESPONSE REGULATOR 1 (ARR1) and ARR12 directly upregulate the expression of ROOT HAIR DEFECTIVE 6-LIKE 4 (RSL4), which encodes a key transcription factor that controls root hair elongation. However, depending on the nutrient availability, it is unknown whether the ARR1/12–RSL4 pathway controls root hair elongation. This study shows that phosphate deficiency induced the expression of RSL4 and increased the root hair length through ARR1/12, though the transcript and protein levels of ARR1/12 did not change. These results indicate that cytokinins, together with other hormones, regulate root hair growth under phosphate starvation conditions.

Phytohormones in the regulation on growth and development of water ferns of Salviniaceae family: a review

Water ferns of the Salviniaceae family are successfully used for bioremediation and bioindication of contaminated waters. Due to intensive propagation they are able to produce a great volume of biomass enriched with natural plant growth regulators. Simultaneously, water ferns have become an impediment to the use of water resources through the fast spread. Their growth and development is under control of phytohormones, which are main chemical messengers regulating the responses to environmental changes. Today hormonal system of water ferns of the Salviniaceae family remains understudied. In this review, we analyzed and summarized the literature data and the results of our own research about the role of auxins, cytokinins, gibberellic, abscisic, salicylic and jasmonic acids in regulation of growth and development of water ferns from Salvinia and Azolla genera emphasizing the specific hallmarks of these phytohormones in ferns. We have submitted brief information about methodological approaches for endogenous phytohormones determination in water ferns of the Salviniaceae family. The effects of exogenous regulators on growth, development and tolerance of water macrophytes from Salvinia and Azolla genera were discussed, as well as the possibility of using water ferns to create ecological biofertilizers.

Apical Dominance and Branching in Plantlets of Colt Cherry Lines Expressing Different Light and Auxin Signalling Sensitivities

The establishment of plant architecture requires coordination of distinct processes including shoot branching and apical dominance (AD). AD involves the bud apical shoot, mainly through indole-3-acetic acid (IAA) synthetized by the cells of the meristem and young leaves. The rootward flow generates an auxin gradient in the stem and buds, regulating lateral bud (LB) outgrowth. Phytochromes and AD are involved in the shade-avoidance syndrome in woody plants. However, the underlying mechanisms remain poorly understood. The aim of this study was to evaluate the sensitivity of cherry rootstocks to light, mediated by the photoreceptor phytochrome, and its effect on the role of auxin in driving branching by AD. Pharmacological treatments using transport inhibitors and a competitor of IAA were applied to transgenic lines of Colt cherry rootstock, which showed different sensitivities to light because of the ectopic expression of a rice phyA gene. Results showed different physiological behaviours among the transgenic lines and between themselves and the Colt-wt line. Exogenous IBA inhibited Colt-wt LB outgrowth, and this inhibition was less intense in transgenic lines. The IAA-inhibitors and IAA-competitor promoted branching. In in vitro phyA-transgenic plantlets, the ectopic gene induced greater branching and a higher number of buds developed in new shoots. This work confirms a positive action of phytochrome on lateral branching in cherry rootstock, playing a role in the regulation of AD. Moreover, we suggest that the confined in vitro system might now be used as a phenotyping screening to test the plasticity of the response, highlighting the behaviour of modified genotypes due to an ectopic insertion event by simple and rapid procedures.

The AUX1-AFB1-CNGC14 module establishes a longitudinal root surface pH profile.

Plant roots navigate in the soil environment following the gravity vector. Cell divisions in the meristem and rapid cell growth in the elongation zone propel the root tips through the soil. Actively elongating cells acidify their apoplast to enable cell wall extension by the activity of plasma membrane AHA H+-ATPases. The phytohormone auxin, central regulator of gravitropic response and root development, inhibits root cell growth, likely by rising the pH of the apoplast. However, the role of auxin in the regulation of the apoplastic pH gradient along the root tip is unclear. Here, we show, by using an improved method for visualization and quantification of root surface pH, that the Arabidopsis thaliana root surface pH shows distinct acidic and alkaline zones, which are not primarily determined by the activity of AHA H+-ATPases. Instead, the distinct domain of alkaline pH in the root transition zone is controlled by a rapid auxin response module, consisting of the AUX1 auxin influx carrier, the AFB1 auxin co-receptor, and the CNCG14 calcium channel. We demonstrate that the rapid auxin response pathway is required for an efficient navigation of the root tip.

Role of Auxin in vegetative growth, flowering, yield and fruit quality of Horticultural crops - A review

Role of Auxin in vegetative growth, flowering, yield and fruit quality of Horticultural crops - A review

Role of Auxin in vegetative growth, flowering, yield and fruit quality of Horticultural crops - A review

Role of Auxin in vegetative growth, flowering, yield and fruit quality of Horticultural crops - A review

HSP90 in morphogenesis: taking the heat and keeping the dark.

This article is a Commentary on Zeng et al. (2023), 239: 1253–1265.

How flower development genes were identified using forward genetic screens in Arabidopsis thaliana.

In the later part of the 1980s, the time was ripe for identifying genes controlling flower development. In that pregenomic era, the easiest way to do this was to induce random mutations in seeds by chemical mutagens (or irradiation) and to screen thousands of plants for those with phenotypes specifically defective in floral morphogenesis. Here, we discuss the results of premolecular screens for flower development mutants in Arabidopsis thaliana, carried out at Caltech and Monash University, emphasizing the usefulness of saturation mutagenesis, multiple alleles to identify full loss-of-function, conclusions based on multiple mutant analyses, and from screens for enhancer and suppressor modifiers of original mutant phenotypes. One outcome was a series of mutants that led to the ABC floral organ identity model (AP1, AP2, AP3, PI, and AG). In addition, genes controlling flower meristem identity (AP1, CAL, and LFY), floral meristem size (CLV1 and CLV3), development of individual floral organ types (CRC, SPT, and PTL), and inflorescence meristem properties (TFL1, PIN1, and PID) were defined. These occurrences formed targets for cloning that eventually helped lead to an understanding of transcriptional control of the identity of floral organs and flower meristems, signaling within meristems, and the role of auxin in initiating floral organogenesis. These findings in Arabidopsis are now being applied to investigate how orthologous and paralogous genes act in other flowering plants, allowing us to wander in the fertile fields of evo-devo.

РОЛЬ АУКСИНОВ И ИХ ПЕРЕНОСЧИКОВ ПРИ НИЗКОЙ ИНТЕНСИВНОСТИ СВЕТА В РЕГУЛЯЦИИ ВЕТВЛЕНИЯ КОРНЕЙ ПШЕНИЦЫ

Light is vital for any plant, so there are many mechanisms for adapting to its deficiency. For example, when shading by other plants, the stems are elongated due to the resources going to other organs, in particular, roots, the branching of which may decrease. The decrease in root branching under the influence of low light is explained by a decrease in auxin transport (IAA) from shoots to roots. However, data on the effect of low light on auxins is rather contradictory. The data obtained in this work indicate a decrease in the concentration of auxins in the roots and phloem exudate of plants at low light intensity, which indicates the role of auxins in the transmission of a signal from the shoot about this external factor and its effect on the level of auxins in roots. The root growth response to low light was manifested as a decrease in branching, and since auxins are known to be required to induce lateral root growth, this low light effect appears to be related to the long-range signal from the leaves in the form of reduced delivery of auxins through the phloem.

Role of auxin in the symbiotic relationship between Piriformospora indica and rice plants

Piriformospora indica (P. indica) is a beneficial endophytic fungus colonized with roots of a wide range of host plant species; however, the mechanisms of P. indica symbiosis with different plants could vary and need to be further addressed. Our study showed that root architecture and growth behaviors were changed in P. indica-colonized rice plants. The P. indica-induced primary root shorting and coiling phenomena were consistent with the auxin-responsive phenotype, suggesting that the auxin levels of P. indica-colonized roots were modulated. To investigate the changes in auxin levels, auxin-responsive gene expressions and promoter activities were used as indicators to monitor auxin levels in root tissues. The results showed that the auxin levels of primary roots were increased in P. indica-inoculated seedlings. Furthermore, an auxin inhibitor (p-chlorophenoxyisobutyric acid, PCIB) was applied to block auxin action to confirm whether auxin is a critical factor in regulating P. indica-induced root growth. The P. indica-induced root architecture modification was significantly repressed by PCIB which was added to the rice culture solutions at the initiation of P. indica inoculation. A proposed hypothesis was that the PCIB treatment might result in lower colonization and further reduce the influence of P. indica colonization on root architecture. The effect of PCIB on colonization was observed by counting the percent root colonization. The data showed that the colonization levels of P. indica in PCIB-treated seedlings were significantly decreased. Taken together, our data indicated that auxin levels would be increased in P. indica-colonized rice roots. Moreover, it was demonstrated that auxin has dual roles in the symbiotic relationship between rice and P. indica, which is a signal that triggers P. indica-induced root growth and a positive factor involved in the colonization mechanism.

Integration of Auxin, Brassinosteroid and Cytokinin in the Regulation of Rice Yield.

Crop varieties with a high yield are most desirable in the present context of the ever-growing human population. Mostly, the yield traits are governed by a complex of numerous molecular and genetic facets modulated by various quantitative trait loci (QTLs). With the identification and molecular characterizations of yield-associated QTLs over recent years, the central role of phytohormones in regulating plant yield is becoming more apparent. Most often, different groups of phytohormones work in close association to orchestrate yield attributes. Understanding this cross talk would thus provide new venues for phytohormone pyramiding by editing a single gene or QTL(s) for yield improvement. Here, we review a few important findings to integrate the knowledge on the roles of auxin, brassinosteroid and cytokinin and how a single gene or a QTL could govern cross talk among multiple phytohormones to determine the yield traits.

Systemic control of plant regeneration and wound repair.

Plants have a broad capacity to regenerate damaged organs. The study of wounding in multiple developmental systems has uncovered many of the molecular properties underlying plants' competence for regeneration at the local cellular level. However, in nature, wounding is rarely localized to one place, and plants need to coordinate regeneration responses at multiple tissues with environmental conditions and their physiological state. Here, we review the evidence for systemic signals that regulate regeneration on a plant-wide level. We focus on the role of auxin and sugars as short- and long-range signals in natural wounding contexts and discuss the varied origin of these signals in different regeneration scenarios. Together, this evidence calls for a broader, system-wide view of plant regeneration competence.

Roles of Auxin in the Growth, Development, and Stress Tolerance of Horticultural Plants.

Auxin, a plant hormone, regulates virtually every aspect of plant growth and development. Many current studies on auxin focus on the model plant Arabidopsis thaliana, or on field crops, such as rice and wheat. There are relatively few studies on what role auxin plays in various physiological processes of a range of horticultural plants. In this paper, recent studies on the role of auxin in horticultural plant growth, development, and stress response are reviewed to provide novel insights for horticultural researchers and cultivators to improve the quality and application of horticultural crops.

Characterization of miRNA-mediated auxin signaling during banana (Musa spp.) fruit ripening

Auxin signaling is essential for the whole plant life cycle and the core components of auxin signaling include the auxin receptor TIR/AFB, corepressor Aux/IAA, and transcription factor ARF. They jointly modulate a variety of biological processes through regulating the expression of auxin-responsive genes. In the past decades, microRNAs (miRNAs) have been well documented as vital regulators of gene expression. A group of miRNA families have been found to target genes associated with auxin signal transduction, such as TIR/AFBs and ARFs. Banana is a typical climacteric fruit that undergo dramatic physiological and biochemical changes during ripening process. However, the role of auxin itself and miRNAs in auxin signaling during fruit ripening remain largely unknown in banana. In this study, we comprehensively characterized three key gene families of auxin signaling pathways in banana. There are 15 TIR/AFB, 50 Aux/IAA, and 49 ARF genes in the banana genome. Also, we identified multiple miRNAs that can target members of auxin-related gene families, and the targeting relationship and inhibitory effect of miR393, miR160 and miR167 on specific TIR/AFB and ARF family members were further experimentally validated. In addition, the expression analysis of banana pulp after ethylene treatment revealed the specific response of these auxin-related miRNAs to ethylene. Finally, a mode of action of miRNA-mediated auxin signaling in ethylene-induced banana fruit ripening was proposed. Our results not only unraveled the regulation of miRNA on banana auxin response, but also provided a reference for the study of miRNA-mediated auxin signaling in the ripening of climacteric fruit.

New Insights Into the Activity of Apple Dihydrochalcone Phloretin: Disturbance of Auxin Homeostasis as Physiological Basis of Phloretin Phytotoxic Action.

Apple species are the unique naturally rich source of dihydrochalcones, phenolic compounds with an elusive role in planta, but suggested auto-allelochemical features related to “apple replant disease” (ARD). Our aim was to elucidate the physiological basis of the phytotoxic action of dihydrochalcone phloretin in the model plant Arabidopsis and to promote phloretin as a new prospective eco-friendly phytotoxic compound. Phloretin treatment induced a significant dose-dependent growth retardation and severe morphological abnormalities and agravitropic behavior in Arabidopsis seedlings. Histological examination revealed a reduced starch content in the columella cells and a serious disturbance in root architecture, which resulted in the reduction in length of meristematic and elongation zones. Significantly disturbed auxin metabolome profile in roots with a particularly increased content of IAA accumulated in the lateral parts of the root apex, accompanied by changes in the expression of auxin biosynthetic and transport genes, especially PIN1, PIN3, PIN7, and ABCB1, indicates the role of auxin in physiological basis of phloretin-induced growth retardation. The results reveal a disturbance of auxin homeostasis as the main mechanism of phytotoxic action of phloretin. This mechanism makes phloretin a prospective candidate for an eco-friendly bioherbicide and paves the way for further research of phloretin role in ARD.

The role of auxin and giberalin in the growth of black cumin (Nigella sativa L.) by in vitro

As an herbal plant, black cumin (Nigella sativa L.) has been widely used. The seeds are able to overcome various types of diseases including viruses, able to relieve pain (analgesic), anti-swelling (anti-inflammatory), antiallergic (antihistamines), antioxidant, antidiabetic mellitus, antitumor, and anticancer. Propagation of black cumin by in vitro or known as micropropagation is one of the artificial vegetative propagation that can meet the sustainability production for cumin plants in Indonesia. In vitro propagation of black cumin is able to produce large numbers of seeds in a relatively short time, has the same properties as the parent, with a seedling process that is not seasonally dependent. Currently, the study have started using MS media, and modification of the type of tissue culture media by adding 2,4 D of 10 mg/l combination with GA3 of 1 mg/l can increased the percentage of callus growth. The combination of these two types of growth regulators, also influenced the number of shoots, plant height and number of roots.

The Potassium-Dependent Transcriptome Analysis of Maize Provides Novel Insights into the Rescue Role of Auxin in Responses to Potassium Deficiency

Potassium (K+) deficiency is a key factor limiting maize growth and yield. Auxin plays an important role in maize adaptation to K+ deficiency, but its physiological and molecular mechanisms are largely unclear. In this study, the exogenous application of 0.01 μmol·L–1 α-Naphthalene acetic acid (NAA) could effectively alleviate the growth inhibition of maize roots caused by K+ deficiency, especially in the low-K-sensitive maize inbred line D937. The transcriptome results showed that 3924 and 5458 genes were differentially expressed by exogenous NAA in D937 (sensitive to K+ deficiency) and 90-21-3 (tolerant to K+ deficiency) under K+ deficiency, respectively. The exogenous application of NAA to D937 results in maintenance of the indole acetic acid (IAA) levels by inducing an upregulation in the expression of YUCCA-encoding genes and decreases abscisic acid (ABA) content by inducing the differential expression of genes encoding NCED (downregulated), ABA2 (downregulated), and PP2C (upregulated), thereby reducing growth damage caused by K+ deficiency. In 90-21-3, exogenous NAA can decrease ABA content and increase IAA/ABA by inducing the differential expression of CYP707- and ABF-related genes, inhibiting the excess accumulation of reactive oxygen species by inducing the differential expression of genes encoding antioxidant enzymes, and maintain cellular K+ homeostasis by regulating the expression of genes encoding K+ channels and transporters, thus enhancing plant tolerance to K+ deficiency. This study lays the foundation for understanding the molecular mechanisms underlying maize adaptation to K+ deficiency.

Genome-wide identification of Aux/IAA and ARF gene families in bread wheat (Triticum aestivum L.).

Wheat (Triticum aestivum L.) is one of the most important food crops in the world. Somatic embryogenesis is an event that is triggered by the presence of auxin hormone for the induction of somatic cells to get converted to embryonic cells. Somatic embryogenesis represents the most important process of totipotency of plants. The role of auxins is widely understood during various stages of embryogenesis including polarity establishment, de-differentiation, re-differentiations, and morphogenesis. Many of the Aux/IAAs and ARFs which are part of auxin signaling components have been identified to play various roles during embryogenesis. In this analysis, the Aux/IAAs and ARFs of T. aestivum have been analyzed at the genome-scale; their structure, function, and evolutionary relatedness were determined. Several Aux/IAAs and ARFs components of T. aestivum have been found to exclusively regulate axis formation, meristem commitment, and other re-differentiation processes by differential expression studies.

Facilitation of auxin biosynthesis and metabolism by salt stress in rice plants

To investigate the effects of salt stress on the auxin in rice plants, we analyzed indole-3-acetic acid (IAA) and its metabolites in hydroponically grown rice plant seedlings (Oryza sativa cv. Nipponbare) and in the culture medium using LC-ESI/MS/MS. We found that the IAA level in the culture medium was increased 39-fold due to salt stress treatment, while those in the shoots and roots were increased by less than 2-fold. The culture medium also contained high amounts of oxidized metabolites such as OxIAA, DiOxIAA, DiOxIAA-Glu, and DiOxIAA-Asp. The total amount of IAA and its metabolites in the shoots, roots, and culture medium was significantly increased with salt treatment. A salt stress-responsive increase in the IAA metabolites was observed in 9 tested cultivars of rice. The results indicate that salt stress facilitates the metabolic turnover of IAA in rice plants and may open new insight into the role of auxin.