ABSTRACT
The phytohormone strigolactone (SL) inhibits shoot branching, whereas the signalling metabolite trehalose 6-phosphate (Tre6P) promotes branching. How Tre6P and SL signalling may interact and which molecular mechanisms might be involved remains largely unknown. Transcript profiling of Arabidopsis SL mutants revealed a cluster of differentially expressed genes highly enriched in the Tre6P pathway compared with wild-type (WT) plants or brc1 mutants. Tre6P-related genes were also differentially expressed in axillary buds of garden pea (Pisum sativum) SL mutants. Tre6P levels were elevated in the SL signalling mutant more axillary (max) growth 2 compared with other SL mutants or WT plants indicating a role of MAX2-dependent SL signalling in regulating Tre6P levels. A transgenic approach to increase Tre6P levels demonstrated that all SL mutant lines and brc1 flowered earlier, showing all of these mutants were responsive to Tre6P. Elevated Tre6P led to increased branching in WT plants but not in max2 and max4 mutants, indicating some dependency between the SL pathway and Tre6P regulation of shoot branching. By contrast, elevated Tre6P led to an enhanced branching phenotype in brc1 mutants indicating independence between BRC1 and Tre6P. A model is proposed whereby SL signalling represses branching via Tre6P and independently of the BRC1 pathway.
ABSTRACT
Strigolactones (SL) function as plant hormones in control of multiple aspects of plant development, mostly via the regulation of gene expression. Immediate early-gene regulation by SL remains unexplored due to difficulty in dissecting early from late gene expression responses to SL. We used synthetic SL, rac-GR24 treatment of protoplasts and RNA-seq to explore early SL-induced changes in gene expression over time (5-180 minutes) and discovered rapid, dynamic and SL receptor D14-dependent regulation of gene expression in response to rac-GR24. Importantly, we discovered a significant dependence of SL signalling on chromatin remodelling processes, as the induction of a key SL-induced transcription factor BRANCHED1 requires the SWI/SNF chromatin remodelling ATPase SPLAYED (SYD) and leads to upregulation of a homologue SWI/SNF ATPase BRAHMA. ATAC-seq profiling of genome-wide changes in chromatin accessibility in response to rac-GR24 identified large-scale changes, with over 1400 differentially accessible regions. These changes in chromatin accessibility often precede transcriptional changes and are likely to harbour SL cis-regulatory elements. Importantly, we discovered that this early and extensive modification of the chromatin landscape also requires SYD. This study, therefore, provides evidence that SL signalling requires regulation of chromatin accessibility, and it identifies genomic locations harbouring likely SL cis-regulatory sequences.
Subject(s)
Chromatin Assembly and Disassembly , Gene Expression Regulation, Plant , Lactones , Plant Growth Regulators , Lactones/metabolism , Plant Growth Regulators/metabolism , Transcription Factors/metabolism , Transcription Factors/genetics , Arabidopsis/genetics , Arabidopsis/metabolism , Heterocyclic Compounds, 3-Ring/metabolism , Arabidopsis Proteins/genetics , Arabidopsis Proteins/metabolism , Chromatin/metabolism , Chromatin/genetics , Chromosomal Proteins, Non-Histone/genetics , Chromosomal Proteins, Non-Histone/metabolism , Signal TransductionABSTRACT
Plants tightly control growth of their lateral organs, which led to the concept of apical dominance. However, outgrowth of the dormant lateral primordia is sensitive to the plant's nutritional status, resulting in an immense plasticity in plant architecture. While the impact of hormonal regulation on apical dominance is well characterized, the prime importance of sugar signaling to unleash lateral organ formation has just recently emerged. Here, we aimed to identify transcriptional regulators, which control the trade-off between growth of apical versus lateral organs. Making use of locally inducible gain-of-function as well as single and higher-order loss-of-function approaches of the sugar-responsive S1-basic-leucine-zipper (S1-bZIP) transcription factors, we disclosed their largely redundant function in establishing apical growth dominance. Consistently, comprehensive phenotypical and analytical studies of S1-bZIP mutants show a clear shift of sugar and organic nitrogen (N) allocation from apical to lateral organs, coinciding with strong lateral organ outgrowth. Tissue-specific transcriptomics reveal specific clade III SWEET sugar transporters, crucial for long-distance sugar transport to apical sinks and the glutaminase GLUTAMINE AMIDO-TRANSFERASE 1_2.1, involved in N homeostasis, as direct S1-bZIP targets, linking the architectural and metabolic mutant phenotypes to downstream gene regulation. Based on these results, we propose that S1-bZIPs control carbohydrate (C) partitioning from source leaves to apical organs and tune systemic N supply to restrict lateral organ formation by C/N depletion. Knowledge of the underlying mechanisms controlling plant C/N partitioning is of pivotal importance for breeding strategies to generate plants with desired architectural and nutritional characteristics.
Subject(s)
Basic-Leucine Zipper Transcription Factors , Plant Breeding , Basic-Leucine Zipper Transcription Factors/genetics , Basic-Leucine Zipper Transcription Factors/metabolism , Plants/metabolism , Signal Transduction/genetics , Sugars , Gene Expression Regulation, Plant , Plant Proteins/genetics , Plant Proteins/metabolismABSTRACT
There have been substantial advances in our understanding of many aspects of strigolactone regulation of branching since the discovery of strigolactones as phytohormones. These include further insights into the network of phytohormones and other signals that regulate branching, as well as deep insights into strigolactone biosynthesis, metabolism, transport, perception and downstream signaling. In this review, we provide an update on recent advances in our understanding of how the strigolactone pathway co-ordinately and dynamically regulates bud outgrowth and pose some important outstanding questions that are yet to be resolved.
Subject(s)
Indoleacetic Acids , Plant Growth Regulators , Plant Growth Regulators/metabolism , Indoleacetic Acids/metabolism , Plant Shoots/metabolism , Lactones/metabolism , Hormones/metabolismABSTRACT
Basic leucine zipper 11 (bZIP11) is a transcription factor that is activated under low energy conditions in plants and plays a crucial role in enabling plants to adapt to starvation situations. Although previous results indicate that bZIP11 regulates chromatin accessibility based on evidence obtained from single genomic loci, to what extent this transcription factor regulates the chromatin landscape at the whole genome level remains unknown. Here we addressed this by performing an ATAC-seq (Assay for Transposase-Accessible Chromatin with high-throughput sequencing) on Arabidopsis thaliana (Arabidopsis) leaf protoplasts to obtain a profile of chromatin patterning in response upon bZIP11 induction. We identified, on average, 10,000 differentially accessible regions upon bZIP11 induction, corresponding to over 8,420 different genes out of the 25,000 genes present in the Arabidopsis genome. Our study provides a resource for understanding how bZIP11 regulates the genome at the chromatin level and provides an example of the impact of a single transcription factor on a whole plant genome.
Subject(s)
Arabidopsis , Chromatin , Arabidopsis/genetics , Chromatin/genetics , Chromatin Immunoprecipitation Sequencing , Genome, Plant , High-Throughput Nucleotide Sequencing , Sequence Analysis, DNA , Transcription Factors/geneticsABSTRACT
The process of apical dominance by which the apical bud/shoot tip of the plant inhibits the outgrowth of axillary buds located below has been studied for more than a century. Different approaches were used over time, with first the physiology era, the genetic era, and then the multidisciplinary era. During the physiology era, auxin was thought of as the master regulator of apical dominance acting indirectly to inhibit bud outgrowth via unknown secondary messenger(s). Potential candidates were cytokinin (CK) and abscisic acid (ABA). The genetic era with the screening of shoot branching mutants in different species revealed the existence of a novel carotenoid-derived branching inhibitor and led to the significant discovery of strigolactones (SLs) as a novel class of plant hormones. The re-discovery of the major role of sugars in apical dominance emerged from modern physiology experiments and involves ongoing work with genetic material affected in sugar signalling. As crops and natural selection rely on the emergent properties of networks such as this branching network, future work should explore the whole network, the details of which are critical but not individually sufficient to solve the 'wicked problems' of sustainable food supply and climate change.
Subject(s)
Cytokinins , Plant Growth Regulators , Plant Shoots , Plant Growth Regulators/physiology , Indoleacetic Acids/pharmacology , Abscisic Acid , Sugars , Gene Expression Regulation, PlantABSTRACT
Strigolactones regulate shoot branching and many aspects of plant growth, development, and allelopathy. Strigolactones are often discussed alongside auxin because they work together to inhibit shoot branching. However, the roles and mechanisms of strigolactones and how they act independently of auxin are still elusive. Additionally, there is still much in general to be discovered about the network of molecular regulators and their interactions in response to strigolactones. Here, we conducted an experiment in Arabidopsis with physiological treatments and strigolactone mutants to determine transcriptional pathways associated with strigolactones. The three physiological treatments included shoot tip removal with and without auxin treatment and treatment of intact plants with the auxin transport inhibitor, N-1-naphthylphthalamic acid (NPA). We identified the glucosinolate biosynthesis pathway as being upregulated across strigolactone mutants indicating strigolactone-glucosinolate crosstalk. Additionally, strigolactone application cannot restore the highly branched phenotype observed in glucosinolate biosynthesis mutants, placing glucosinolate biosynthesis downstream of strigolactone biosynthesis. Oxidative stress genes were enriched across the experiment suggesting that this process is mediated through multiple hormones. Here, we also provide evidence supporting non-auxin-mediated, negative feedback on strigolactone biosynthesis. Increases in strigolactone biosynthesis gene expression seen in strigolactone mutants could not be fully restored by auxin. By contrast, auxin could fully restore auxin-responsive gene expression increases, but not sugar signaling-related gene expression. Our data also point to alternative roles of the strigolactone biosynthesis genes and potential new signaling functions of strigolactone precursors. In this study, we identify a strigolactone-specific regulation of glucosinolate biosynthesis genes indicating that the two are linked and may work together in regulating stress and shoot ranching responses in Arabidopsis. Additionally, we provide evidence for non-auxinmediated feedback on strigolactone biosynthesis and discuss this in the context of sugar signaling.
ABSTRACT
The inhibition of shoot branching by the growing shoot tip of plants, termed apical dominance, was originally thought to be mediated by auxin. Recently, the importance of the shoot tip sink strength during apical dominance has re-emerged with recent studies highlighting roles for sugars in promoting branching. This raises many unanswered questions on the relative roles of auxin and sugars in apical dominance. Here we show that auxin depletion after decapitation is not always the initial trigger of rapid cytokinin (CK) increases in buds that are instead correlated with enhanced sugars. Auxin may also act through strigolactones (SLs) which have been shown to suppress branching after decapitation, but here we show that SLs do not have a significant effect on initial bud outgrowth after decapitation. We report here that when sucrose or CK is abundant, SLs are less inhibitory during the bud release stage compared to during later stages and that SL treatment rapidly inhibits CK accumulation in pea (Pisum sativum) axillary buds of intact plants. After initial bud release, we find an important role of gibberellin (GA) in promoting sustained bud growth downstream of auxin. We are, therefore, able to suggest a model of apical dominance that integrates auxin, sucrose, SLs, CKs, and GAs and describes differences in signalling across stages of bud release to sustained growth.
Subject(s)
Decapitation , Plant Growth Regulators , Plant Growth Regulators/pharmacology , Indoleacetic Acids/pharmacology , Cytokinins/pharmacology , Sucrose/pharmacology , Sugars/pharmacology , Pisum sativum , Plant Shoots , Gene Expression Regulation, PlantABSTRACT
The quantification of plant hormones and related gene expression is essential to improve the understanding of the molecular regulation of plant growth and development. However, plant hormone quantification is still challenging due to extremely low endogenous levels and high chemical diversity. In this study, we present a convenient extraction protocol that enables the simultaneous extraction of both phytohormones and RNA from the same sample in a small quantity (approximately 10 mg). Using ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS), this protocol provides a method to quantify 13 phytohormones and their derivatives from four classes (cytokinin, auxin, abscisic acid, and gibberellin) at the speed of 14 min per sample.
ABSTRACT
The strigolactone (SL) class of phytohormones shows broad chemical diversity, the functional importance of which remains to be fully elucidated, along with the enzymes responsible for the diversification of the SL structure. Here we explore the functional evolution of the highly conserved CYP711A P450 family, members of which catalyze several key monooxygenation reactions in the strigolactone pathway. Ancestral sequence reconstruction was utilized to infer ancestral CYP711A sequences based on a comprehensive set of extant CYP711 sequences. Eleven ancestral enzymes, corresponding to key points in the CYP711A phylogenetic tree, were resurrected and their activity was characterized towards the native substrate carlactone and the pure enantiomers of the synthetic strigolactone analogue, GR24. The ancestral and extant CYP711As tested accepted GR24 as a substrate and catalyzed several diversifying oxidation reactions on the structure. Evidence was obtained for functional divergence in the CYP711A family. The monocot group 3 ancestor, arising from gene duplication events within monocot grasses, showed both increased catalytic activity towards GR24 and high stereoselectivity towards the GR24 isomer resembling strigol-type SLs. These results are consistent with a role for CYP711As in strigolactone diversification in early land plants, which may have extended to the diversification of strigol-type SLs.
Subject(s)
Gene Duplication , Poaceae , Heterocyclic Compounds, 3-Ring , Lactones/metabolism , Phylogeny , Plant Growth Regulators/metabolism , Poaceae/genetics , Poaceae/metabolismABSTRACT
Shoot branching is a complex mechanism in which secondary shoots grow from buds that are initiated from meristems established in leaf axils. The model plant Arabidopsis (Arabidopsis thaliana) has a rosette leaf growth pattern in the vegetative stage. After flowering initiation, the main stem elongates with the top leaf primordia developing into cauline leaves. Meristems in Arabidopsis initiate in the axils of rosette or cauline leaves, giving rise to rosette or cauline buds, respectively. Plasticity in the process of shoot branching is regulated by resource and nutrient availability as well as by plant hormones. However, few studies have attempted to test whether cauline and rosette branching are subject to the same plasticity. Here, we addressed this question by phenotyping cauline and rosette branching in three Arabidopsis ecotypes and several Arabidopsis mutants with varied shoot architectures. Our results showed no negative correlation between cauline and rosette branch numbers in Arabidopsis, demonstrating that there is no tradeoff between cauline and rosette bud outgrowth. Through investigation of the altered branching pattern of flowering pathway mutants and Arabidopsis ecotypes grown in various photoperiods and light regimes, we further elucidated that the number of cauline branches is closely related to flowering time. The number of rosette branches has an enormous plasticity compared with cauline branches and is influenced by genetic background, flowering time, light intensity, and temperature. Our data reveal different levels of plasticity in the regulation of branching at rosette and cauline nodes, and promote a framework for future branching analyses.
Subject(s)
Arabidopsis/anatomy & histology , Arabidopsis/growth & development , Arabidopsis/genetics , Flowers/growth & development , Meristem/growth & development , Plant Leaves/growth & development , Plant Shoots/growth & development , Ecotype , Flowers/anatomy & histology , Flowers/genetics , Gene Expression Regulation, Plant , Genes, Plant , Genetic Variation , Meristem/anatomy & histology , Meristem/genetics , Phenotype , Photoperiod , Plant Leaves/anatomy & histology , Plant Leaves/genetics , Plant Shoots/anatomy & histology , Plant Shoots/geneticsABSTRACT
Shoot branching is regulated by multiple signals. Previous studies have indicated that sucrose may promote shoot branching through suppressing the inhibitory effect of the hormone strigolactone (SL). However, the molecular mechanisms underlying this effect are unknown. Here, we used molecular and genetic tools to identify the molecular targets underlying the antagonistic interaction between sucrose and SL. We showed that sucrose antagonizes the suppressive action of SL on tillering in rice and on the degradation of D53, a major target of SL signalling. Sucrose inhibits the gene expression of D3, the orthologue of the Arabidopsis F-box MAX2 required for SL signalling. Overexpression of D3 antagonizes sucrose inhibition of D53 degradation and enables the SL inhibition of tillering under high sucrose. Sucrose prevents SL-induced degradation of D14, the SL receptor involved in D53 degradation. In contrast to D3, D14 overexpression enhances D53 protein levels and sucrose-induced tillering, even in the presence of SL. Our results show that sucrose inhibits SL response by affecting key components of SL signalling and, together with previous studies reporting the inhibition of SL synthesis by nitrate and phosphate, demonstrate the central role played by SLs in the regulation of plant architecture by nutrients.
Subject(s)
Arabidopsis , Oryza , Arabidopsis/genetics , Gene Expression Regulation, Plant , Lactones/metabolism , Lactones/pharmacology , Oryza/metabolism , Plant Proteins/genetics , Plant Proteins/metabolism , Sucrose/metabolism , Sucrose/pharmacologyABSTRACT
Natural selection is responsible for much of the diversity we see in nature. Just as it drives the evolution of new traits, it can also lead to new species. However, it is unclear whether natural selection conferring adaptation to local environments can drive speciation through the evolution of hybrid sterility between populations. Here, we show that adaptive divergence in shoot gravitropism, the ability of a plant's shoot to bend upwards in response to the downward pull of gravity, contributes to the evolution of hybrid sterility in an Australian wildflower, Senecio lautus We find that shoot gravitropism has evolved multiple times in association with plant height between adjacent populations inhabiting contrasting environments, suggesting that these traits have evolved by natural selection. We directly tested this prediction using a hybrid population subjected to eight rounds of recombination and three rounds of selection in the field. Our experiments revealed that shoot gravitropism responds to natural selection in the expected direction of the locally adapted population. Using the advanced hybrid population, we discovered that individuals with extreme differences in gravitropism had more sterile crosses than individuals with similar gravitropic responses, which were largely fertile, indicating that this adaptive trait is genetically correlated with hybrid sterility. Our results suggest that natural selection can drive the evolution of locally adaptive traits that also create hybrid sterility, thus revealing an evolutionary connection between local adaptation and the origin of new species.
Subject(s)
Gravitropism/physiology , Infertility , Plant Shoots/physiology , Senecio/physiology , Adaptation, Physiological/genetics , Adaptation, Physiological/physiology , Arabidopsis Proteins , Australia , Genetic Variation , Indoleacetic Acids/metabolism , Phenotype , Selection, Genetic , Senecio/genetics , SulfurtransferasesABSTRACT
DWARF53 (D53) in rice (Oryza sativa) and its homologs in Arabidopsis (Arabidopsis thaliana), SUPPRESSOR OF MAX2-LIKE 6 (SMXL6), SMXL7 and SMXL8, are well established negative regulators of strigolactone (SL) signalling in shoot branching regulation. Little is known of pea (Pisum sativum) homologs and whether D53 and related SMXLs are specific to SL signalling pathways. Here, we identify two allelic pea mutants, dormant3 (dor3), and demonstrate through gene mapping and sequencing that DOR3 corresponds to a homolog of D53 and SMXL6/SMXL7, designated PsSMXL7. Phenotype analysis, gene expression, protein and hormone quantification assays were performed to determine the role of PsSMXL7 in regulation of bud outgrowth and the role of PsSMXL7 and D53 in integrating SL and cytokinin (CK) responses. Like D53 and related SMXLs, we show that PsSMXL7 can be degraded by SL and induces feedback upregulation of PsSMXL7 transcript. Here we reveal a system conserved in pea and rice, whereby CK also upregulates PsSMXL7/D53 transcripts, providing a clear mechanism for SL and CK cross-talk in the regulation of branching. To further deepen our understanding of the branching network in pea, we provide evidence that SL acts via PsSMXL7 to modulate auxin content via PsAFB5, which itself regulates expression of SL biosynthesis genes. We therefore show that PsSMXL7 is key to a triple hormone network involving an auxin-SL feedback mechanism and SL-CK cross-talk.
Subject(s)
Heterocyclic Compounds, 3-Ring/metabolism , Lactones/metabolism , Pisum sativum/growth & development , Plant Proteins/genetics , Arabidopsis/genetics , Arabidopsis/metabolism , Co-Repressor Proteins/genetics , Co-Repressor Proteins/metabolism , Cytokinins/metabolism , Feedback, Physiological , Gene Expression Regulation, Plant , Indoleacetic Acids/metabolism , Loss of Function Mutation , Oryza , Pisum sativum/genetics , Pisum sativum/metabolism , Phylogeny , Plant Proteins/metabolism , Plants, Genetically Modified , Signal Transduction/geneticsABSTRACT
Plant architecture is controlled by several endogenous signals including hormones and sugars. However, only little information is known about the nature and roles of the sugar signalling pathways in this process. Here we test whether the sugar signalling pathway mediated by HEXOKINASE1 (HXK1) is involved in the control of shoot branching. To test the involvement of HXK1 in shoot branching and in the hormonal network controlling this process, we modulated the HXK1 pathway using physiological and genetic approaches in rose, pea and arabidopsis. Mannose-induced HXK signalling triggered bud outgrowth in rose and pea. In arabidopsis, both HXK1 deficiency and defoliation led to decreased shoot branching and conferred hypersensitivity to auxin. Complementation of the HXK1 knockout mutant gin2 with a catalytically inactive HXK1, restored shoot branching to the wild-type level. HXK1-deficient plants displayed decreased cytokinin levels and increased expression of MAX2, which is required for strigolactone signalling. The branching phenotype of HXK1-deficient plants could be partly restored by cytokinin treatment and strigolactone deficiency could override the negative impact of HXK1 deficiency on shoot branching. Our observations demonstrate that HXK1 signalling contributes to the regulation of shoot branching and interacts with hormones to modulate plant architecture.
Subject(s)
Cytokinins , Indoleacetic Acids , Gene Expression Regulation, Plant , Heterocyclic Compounds, 3-Ring , Lactones/pharmacology , Plant Growth Regulators , Plant ShootsABSTRACT
Trehalose 6-phosphate (Tre6P) is a sucrose signalling metabolite that has been implicated in regulation of shoot branching, but its precise role is not understood. We expressed tagged forms of TREHALOSE-6-PHOSPHATE SYNTHASE1 (TPS1) to determine where Tre6P is synthesized in arabidopsis (Arabidopsis thaliana), and investigated the impact of localized changes in Tre6P levels, in axillary buds or vascular tissues, on shoot branching in wild-type and branching mutant backgrounds. TPS1 is expressed in axillary buds and the subtending vasculature, as well as in the leaf and stem vasculature. Expression of a heterologous Tre6P phosphatase (TPP) to lower Tre6P in axillary buds strongly delayed bud outgrowth in long days and inhibited branching in short days. TPP expression in the vasculature also delayed lateral bud outgrowth and decreased branching. Increased Tre6P in the vasculature enhanced branching and was accompanied by higher expression of FLOWERING LOCUS T (FT) and upregulation of sucrose transporters. Increased vascular Tre6P levels enhanced branching in branched1 but not in ft mutant backgrounds. These results provide direct genetic evidence of a local role for Tre6P in regulation of axillary bud outgrowth within the buds themselves, and also connect Tre6P with systemic regulation of shoot branching via FT.
Subject(s)
Arabidopsis , Sugar Phosphates , Arabidopsis/genetics , Gene Expression Regulation, Plant , Phosphates , Plant Shoots , Trehalose/analogs & derivativesABSTRACT
Phytohormones are involved in most plant physiological processes and the quantification of endogenous phytohormone levels and related gene expressions is an important approach to studying phytohormone functions. However, the quantification of phytohormones is still challenging due to their extremely low endogenous level in plant tissues and their high chemical diversity. Therefore, developing a method to simultaneously quantify phytohormone levels and RNA would strongly facilitate comparative analyses of phytohormones and gene expression. The present work reports a convenient extraction protocol enabling multivariate analysis of phytohormones and RNA from small amounts of plant material (around 10 mg). This high-throughput ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method demonstrates quantification of phytohormones and their related metabolites from four plant hormone classes: cytokinin, auxin, abscisic acid, and gibberellin. The UPLC-MS/MS method can quantify thirteen phytohormones and their metabolites simultaneously in 14 min. To validate the developed method, we determined the dynamic profiles of phytohormones and gene expressions in small axillary shoot buds in garden pea. This new method is applicable to quantification analysis of gene expression and multiple phytohormone classes in small amounts of plant materials. The results obtained using this method in axillary buds provide a basis for understanding the phytohormone functions in shoot branching regulation.
ABSTRACT
Strigolactones are plant hormones and rhizosphere signaling molecules with key roles in plant development, mycorrhizal fungal symbioses, and plant parasitism. Currently, sensitive, specific, and high-throughput methods of detecting strigolactones are limited. Here, we developed genetically encoded fluorescent strigolactone biosensors based on the strigolactone receptors DAD2 from Petunia hybrida, and HTL7 from Striga hermonthica. The biosensors were constructed via domain insertion of circularly permuted GFP. The biosensors exhibited loss of cpGFP fluorescence in vitro upon treatment with the strigolactones 5-deoxystrigol and orobanchol, or the strigolactone analogue rac-GR24, and the ShHTL7 biosensor also responded to a specific antagonist. To overcome biosensor sensitivity to changes in expression level and protein degradation, an additional strigolactone-insensitive fluorophore, LSSmOrange, was included as an internal normalization control. Other plant hormones and karrikins resulted in no fluorescence change, demonstrating that the biosensors report on compounds that specifically bind the SL receptors. The DAD2 biosensor likewise responded to strigolactones in an in vivo protoplast system, and retained strigolactone hydrolysis activity. These biosensors have applications in high-throughput screening for agrochemical compounds, and may also have utility in understanding strigolactone mediated signaling in plants.
Subject(s)
Biosensing Techniques/methods , Heterocyclic Compounds, 3-Ring/analysis , Lactones/analysis , Plant Proteins/metabolism , Biocatalysis , Gene Expression/drug effects , Green Fluorescent Proteins/genetics , Green Fluorescent Proteins/metabolism , Heterocyclic Compounds, 3-Ring/metabolism , Heterocyclic Compounds, 3-Ring/pharmacology , Lactones/metabolism , Lactones/pharmacology , Petunia/metabolism , Plant Proteins/antagonists & inhibitors , Plant Proteins/genetics , Protein Domains , Proteolysis/drug effects , Recombinant Fusion Proteins/biosynthesis , Recombinant Fusion Proteins/genetics , Striga/metabolismABSTRACT
Strigolactones (SLs) control plant development, enhance symbioses, and act as germination stimulants for some of the most destructive species of parasitic weeds, making SLs a potential tool to improve crop productivity and resilience. Field trials demonstrate the potential use of SLs as agrochemicals or genetic targets in breeding programs, with applications in improving drought tolerance, increasing yields, and controlling parasitic weeds. However, for effective translation of SLs into agriculture, understanding and exploiting SL diversity and the development of economically viable sources of SL analogs will be critical. Here we review how manipulation of SL signaling can be used when developing new tools and crop varieties to address some critical challenges, such as nutrient acquisition, resource allocation, stress tolerance, and plant-parasite interactions.
Subject(s)
Lactones , Plant Growth Regulators , Agriculture , Germination , Plant WeedsABSTRACT
Strigolactones (SLs) regulate important aspects of plant growth and stress responses. Many diverse types of SL occur in plants, but a complete picture of biosynthesis remains unclear. In Arabidopsis thaliana, we have demonstrated that MAX1, a cytochrome P450 monooxygenase, converts carlactone (CL) into carlactonoic acid (CLA) and that LBO, a 2-oxoglutarate-dependent dioxygenase, can convert methyl carlactonoate (MeCLA) into a metabolite called [MeCLA + 16 Da]. In the present study, feeding experiments with deuterated MeCLAs revealed that [MeCLA + 16 Da] is hydroxymethyl carlactonoate (1'-HO-MeCLA). Importantly, this LBO metabolite was detected in plants. Interestingly, other related compounds, methyl 4-hydroxycarlactonoate (4-HO-MeCLA) and methyl 16-hydroxycarlactonoate (16-HO-MeCLA), were also found to accumulate in lbo mutants. 3-HO-, 4-HO-, and 16-HO-CL were detected in plants, but their expected corresponding metabolites, HO-CLAs, were absent in max1 mutants. These results suggest that HO-CL derivatives may be predominant SLs in Arabidopsis, produced through MAX1 and LBO.