Dynamics of Auxin and Cytokinin Metabolism during Early Root and Hypocotyl Growth in Theobroma cacao.
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SUBMITTER: Mboene Noah A
PROVIDER: S-EPMC8151989 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Plant stem-cell pools, the source for all organs, are first established during embryogenesis. It has been known for decades that cytokinin and auxin interact to control organ regeneration in cultured tissue. Auxin has a critical role in root stem-cell specification in zygotic embryogenesis, but the early embryonic function of cytokinin is obscure. Here, we introduce a synthetic reporter to visualize universally cytokinin output in vivo. Notably, the first embryonic signal is detected in the hypophysis, the founder cell of the root stem-cell system. Its apical daughter cell, the precursor of the quiescent centre, maintains phosphorelay activity, whereas the basal daughter cell represses signalling output. Auxin activity levels, however, exhibit the inverse profile. Furthermore, we show that auxin antagonizes cytokinin output in the basal cell lineage by direct transcriptional activation of ARABIDOPSIS RESPONSE REGULATOR genes, ARR7 and ARR15, feedback repressors of cytokinin signalling. Loss of ARR7 and ARR15 function or ectopic cytokinin signalling in the basal cell during early embryogenesis results in a defective root stem-cell system. These results provide a molecular model of transient and antagonistic interaction between auxin and cytokinin critical for specifying the first root stem-cell niche.
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Project description:Interactions between plant hormones and environmental signals are important for the maintenance of root growth plasticity under ever-changing environmental conditions. Here, we demonstrate that arsenate (AsV), the most prevalent form of arsenic (As) in nature, restrains elongation of the primary root through transcriptional regulation of local auxin biosynthesis genes in the root tips of Arabidopsis (Arabidopsis thaliana) plants. The ANTHRANILATE SYNTHASE ALPHA SUBUNIT 1 (ASA1) and BETA SUBUNIT 1 (ASB1) genes encode enzymes that catalyze the conversion of chorismate to anthranilate (ANT) via the tryptophan-dependent auxin biosynthesis pathway. Our results showed that AsV upregulates ASA1 and ASB1 expression in root tips, and ASA1- and ASB1-mediated auxin biosynthesis is involved in AsV-induced root growth inhibition. Further investigation confirmed that AsV activates cytokinin signaling by stabilizing the type-B ARABIDOPSIS RESPONSE REGULATOR1 (ARR1) protein, which directly promotes the transcription of ASA1 and ASB1 genes by binding to their promoters. Genetic analysis revealed that ASA1 and ASB1 are epistatic to ARR1 in the AsV-induced inhibition of primary root elongation. Overall, the results of this study illustrate a molecular framework that explains AsV-induced root growth inhibition via crosstalk between two major plant growth regulators, auxin and cytokinin.
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Project description:A hallmark of plants is their adaptability of size and form in response to widely fluctuating environments. The metabolism and redistribution of the phytohormone auxin play pivotal roles in establishing active auxin gradients and resulting cellular differentiation. In Arabidopsis thaliana, cotyledons and leaves synthesize indole-3-acetic acid (IAA) from tryptophan through indole-3-pyruvic acid (3-IPA) in response to vegetational shade. This newly synthesized auxin moves to the hypocotyl where it induces elongation of hypocotyl cells. Here we show that loss of function of VAS2 (IAA-amido synthetase Gretchen Hagen 3 (GH3).17) leads to increases in free IAA at the expense of IAA-Glu (IAA-glutamate) in the hypocotyl epidermis. This active IAA elicits shade- and high temperature-induced hypocotyl elongation largely independently of 3-IPA-mediated IAA biosynthesis in cotyledons. Our results reveal an unexpected capacity of local auxin metabolism to modulate the homeostasis and spatial distribution of free auxin in specialized organs such as hypocotyls in response to shade and high temperature.
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Project description:Auxin acts synergistically with cytokinin to control the shoot stem-cell niche, while both hormones act antagonistically to maintain the root meristem. In aluminum (Al) stress-induced root growth inhibition, auxin plays an important role. However, the role of cytokinin in this process is not well understood. In this study, we show that cytokinin enhances root growth inhibition under stress by mediating Al-induced auxin signaling. Al stress triggers a local cytokinin response in the root-apex transition zone (TZ) that depends on IPTs, which encode adenosine phosphate isopentenyltransferases and regulate cytokinin biosynthesis. IPTs are up-regulated specifically in the root-apex TZ in response to Al stress and promote local cytokinin biosynthesis and inhibition of root growth. The process of root growth inhibition is also controlled by ethylene signaling which acts upstream of auxin. In summary, different from the situation in the root meristem, auxin acts with cytokinin in a synergistic way to mediate aluminum-induced root growth inhibition in Arabidopsis.
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Project description:BackgroundThe root architecture of grafted apple (Malus spp.) is affected by various characteristics of the scions. To provide information on the molecular mechanisms underlying this influence, we examined root transcriptomes of M. robusta rootstock grafted with scions of wild-type (WT) apple (M. spectabilis) and a more-branching (MB) mutant at the branching stage.ResultsThe growth rate of rootstock grafted MB was repressed significantly, especially the primary root length and diameter, and root weight. Biological function categories of differentially expressed genes were significantly enriched in processes associated with hormone signal transduction and intracellular activity, with processes related to the cell cycle especially down-regulated. Roots of rootstock grafted with MB scions displayed elevated auxin and cytokinin contents and reduced expression of MrPIN1, MrARF, MrAHP, most MrCRE1 genes, and cell growth-related genes MrGH3, MrSAUR and MrTCH4. Although auxin accumulation and transcription of MrPIN3, MrALF1 and MrALF4 tended to induce lateral root formation in MB-grafted rootstock, the number of lateral roots was not significantly changed. Sucrose, fructose and glucose contents were not decreased in MB-grafted roots compared with those bearing WT scions, but glycolysis and tricarboxylic acid cycle metabolic activities were repressed. Root resistance and nitrogen metabolism were reduced in MB-grafted roots as well.ConclusionsOur findings suggest that root growth and development of rootstock are mainly influenced by sugar metabolism and auxin and cytokinin signaling pathways. This study provides a basis that the characteristics of scions are related to root growth and development, resistance and activity of rootstocks.
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Project description:IntroductionStrigolactone (SL) and auxin are two important phytohormones involved in plant root development, but whether they show synergistic or mutual promotion effects during adventitious root (AR) formation has not been adequately explored.MethodsIn this study, we investigated the mechanisms of GR24 (synthetic SL) and indole-3-acetic acid (IAA; a type of auxin) in the formation of ARs using melon as the study material.ResultsMorphological measurements showed that the AR number, length, superficial area, and volume under the GR24 treatment were 1.60-3.27, 1.58-3.99, 2.06-3.42, and 3.00-6.11 times greater than those of the control group, respectively, at 6-10 days; the GR24+IAA treatment further promoted AR formation in melon seedlings, and the AR number, length, superficial area, and volume under the GR24+IAA treatment were 1.44-1.51, 1.28-1.73, 1.19-1.83, and 1.31-1.87 times greater than those obtained with the GR24 treatment, respectively. Transcriptome analysis revealed 2,742, 3,352, and 2,321 differentially expressed genes (DEGs) identified from the GR24 vs. control, GR24+IAA vs. control, and GR24+IAA vs. GR24 comparisons, respectively. The GR24 treatment and GR24+IAA treatment affected auxin and SL synthesis as well as components of the phytohormone signal transduction pathway, such as auxin, brassinosteroid (BR), ethylene (ETH), cytokinin (CK), gibberellin (GA), and abscisic acid (ABA). The concentrations of auxin, GA, zeatin (ZT), and ABA were evaluated using high-performance liquid chromatography (HPLC). From 6 to 10 days, the auxin, GA, and ZT contents in the GR24 treatment group were increased by 11.48%-15.34%, 11.83%-19.50%, and 22.52%-66.17%, respectively, compared to the control group, and these features were increased by 22.00%-31.20%, 21.29%-25.75%, 51.76%-98.96%, respectively, in the GR24+IAA treatment group compared with the control group. Compared to that in the control, the ABA content decreased by 10.30%-11.83% in the GR24 treatment group and decreased by 18.78%-24.00% in the GR24+IAA treatment group at 6-10 days.DiscussionOur study revealed an interaction between strigolactone and auxin in the induction of AR formation in melon seedlings by affecting the expression of genes related to plant hormone pathways and contents.
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Project description:Tomato is a model and economically important crop plant with little information available about gene expression in roots. Currently, there have only been a few studies that examine hormonal responses in tomato roots and none at a genome-wide level. This study examined the transcriptome atlas of tomato root regions (root tip, lateral roots, and whole roots) and the transcriptional regulation of each root region in response to the plant hormones cytokinin and auxin using Illumina RNA sequencing. More than 165 million 1×54 base pair reads were mapped onto the Solanum lycopersicum reference genome and differential expression patterns in each root region in response to each hormone were assessed. Many novel cytokinin- and auxin-induced and -repressed genes were identified as significantly differentially expressed and the expression levels of several were confirmed by qPCR. A number of these regulated genes represent tomato orthologues of cytokinin- or auxin-regulated genes identified in other species, including CKXs, type-A RRs, Aux/IAAs, and ARFs. Additionally, the data confirm some of the hormone regulation studies for recently examined genes in tomato such as SlIAAs and SlGH3s. Moreover, genes expressed abundantly in each root region were identified which provide a spatial distribution of many classes of genes, including plant defence, secondary metabolite production, and general metabolism across the root. Overall this study presents the first global expression patterns of hormone-regulated transcripts in tomato roots, which will be functionally relevant for future studies directed towards tomato root growth and development.
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Project description:The taxonomy of an actinobacterial strain, designated JJY4T, was established using a polyphasic approach. JJY4T was isolated from the rhizosphere of Chromolaena odorata in Yaoundé (Cameroon) during a project for the selection of biological control agents. Strain JJY4T exhibited antimicrobial activities against bacteria, fungi, and oomycetes. Strain JJY4T also exhibited the traits of plant growth-promoting rhizobacteria such as the solubilization of inorganic phosphate, production of siderophores and indole-3-acetic acid, and 1-aminocyclopropane-1-carboxylate deaminase activity. In planta assays performed on cocoa plantlets confirmed that strain JJY4T exhibited strong abilities to promote plant growth and protect against Phytophthora megakarya, the main causal agent of cocoa pod rot. The formation of rugose-ornamented spores in spiral spore chains by strain JJY4T is a typical feature of members found in the Streptomyces violaceusniger clade and, similar to some members of the clade, strain JJY4T produces geldanamycin. A phylogenetic analysis based on 16S rRNA gene sequences confirmed this classification and suggests that strain JJY4T be added to the subclade constituted of the type strains Streptomyces malaysiensis DSM 41697T and Streptomyces samsunensis DSM 42010T. However, DNA-DNA relatedness and physiological characteristics allowed for the differentiation of strain JJY4T from its closest phylogenetic relatives. Based on these results, strain JJY4T (=NRRL B-65369, =NBRC 112705) appears to represent a novel species in the S. violaceusniger clade for which the proposed name is Streptomyces cameroonensis sp. nov.
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Project description:The hormones auxin and cytokinin are essential for plant growth and development. Because of the central importance of root and shoot apical meristems in plant growth, auxin/cytokinin interactions have been predominantly analyzed in relation to apical meristem formation and function. In contrast, the auxin/cytokinin interactions during organ growth have remained largely unexplored. Here, we show that a specific interaction between auxin and cytokinin operates in both the root and the shoot where it serves as an additional determinant of plant development. We found that auxin at low concentrations limits the action of cytokinin. An increase in cytokinin level counteracts this inhibitory effect and leads to an inhibition of auxin signaling. At higher concentrations of both hormones, these antagonistic interactions between cytokinin and auxin are absent. Thus, our results reveal a bidirectional and asymmetrical interaction of auxin and cytokinin beyond the bounds of apical meristems. The relation is bidirectional in that both hormones exert inhibitory effects on each other's signaling mechanisms. However, this relation is also asymmetrical because under controlled growth conditions, auxin present in nontreated plants suppresses cytokinin signaling, whereas the reverse is not the case.
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Project description:The rice root system is important for growth. The crosstalk between auxin and cytokinin mediates root initiation and elongation. However, it remains unclear how the transcriptional network upstream of the auxin and cytokinin signalling pathways determines root development. Here, we observed that the knockdown of OsNAC2, which encodes a NAC transcription factor, increased the primary root length and the number of crown roots. OsNAC2 predominantly expressed in primary root tips, crown roots and lateral root primordia, implying it influences root development. Molecular analyses revealed that the expressions of auxin- and cytokinin-responsive genes were affected in OsNAC2-overexpressing (OsNAC2-OX; ON7 and ON11), RNA interference (OsNAC2-RNAi; RNAi25 and RNAi31) and CRISPR/Cas9 plants. Additionally, OsNAC2 can directly bind to the promoters of IAA inactivation-related genes (GH3.6 and GH3.8), an IAA signalling-related gene (OsARF25), and a cytokinin oxidase gene (OsCKX4). Furthermore, genetic analysis of ON11/osgh3.6 and RNAi31/osckx4 homozygote confirmed that OsCKX4 and OsGH3.6 functioned downstream of OsNAC2. The mRNA levels of CROWN ROOTLESS (CRL) genes and cyclin-dependent protein kinase (CDK) genes increased in OsNAC2-RNAi and OsNAC2-cas9 lines while reduced in OsNAC2-OX lines. Thus, we describe that OsNAC2 functions as an upstream integrator of auxin and cytokinin signals that affect CRL and CDK production to regulate cell division during root development. This novel auxin-OsNAC2-cytokinin model should provide a new insight into the understanding of NAC TFs and crosstalk of auxin and cytokinin pathway, and can be potentially applied in agriculture to enhance rice yields by genetic approaches.
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