Inhibition of shoot branching by new terpenoid plant hormones

Drought-induced molecular changes in crown of various barley phytohormone mutants

One of the main signal transduction pathways that modulate plant growth and stress responses, including drought, is the action of phytohormones. Recent advances in omics approaches have facilitated the exploration of plant genomes. However, the molecular mechanisms underlying the response in the crown of barley, which plays an essential role in plant performance under stress conditions and regeneration after stress treatment, remain largely unclear. The objective of the present study was the elucidation of drought-induced molecular reactions in the crowns of different barley phytohormone mutants. We verified the hypothesis that defects of gibberellins, brassinosteroids, and strigolactones action affect the transcriptomic, proteomic, and hormonal response of barley crown to the transitory drought influencing plant development under stress. Moreover, we assumed that due to the strong connection between strigolactones and branching the hvdwarf14.d mutant, with dysfunctional receptor of strigolactones, manifests the most abundant alternations in crowns and phenotype under drought. Finally, we expected to identify components underlying the core response to drought which are independent of the genetic background. Large-scale analyses were conducted using gibberellins-biosynthesis, brassinosteroids-signaling, and strigolactones-signaling mutants, as well as reference genotypes. Detailed phenotypic evaluation was also conducted. The obtained results clearly demonstrated that hormonal disorders caused by mutations in the HvGA20ox2, HvBRI1, and HvD14 genes affected the multifaceted reaction of crowns to drought, although the expression of these genes was not induced by stress. The study further detected not only genes and proteins that were involved in the drought response and reacted specifically in mutants compared to the reaction of reference genotypes and vice versa, but also the candidates that may underlie the genotype-universal stress response. Furthermore, candidate genes involved in phytohormonal interactions during the drought response were identified. We also found that the interplay between hormones, especially gibberellins and auxins, as well as strigolactones and cytokinins may be associated with the regulation of branching in crowns exposed to drought. Overall, the present study provides novel insights into the molecular drought-induced responses that occur in barley crowns.

Evolution of small molecule-mediated regulation of arbuscular mycorrhiza symbiosis

The arbuscular mycorrhizal (AM) symbiosis formed by most extant land plants with symbiotic fungi evolved 450 Ma. AM promotes plant growth by improving mineral nutrient and water uptake, while the symbiotic fungi obtain carbon in return. A number of plant genes regulating the steps leading to an efficient symbiosis have been identified; however, our understanding of the metabolic processes involved in the symbiosis and how they were wired to symbiosis regulation during plant evolution remains limited. Among them, the exchange of chemical signals, the activation of dedicated biosynthesis pathways and the production of secondary metabolites regulating late stages of the AM symbiosis begin to be well described across several land plant clades. Here, we review our current understanding of these processes and propose future directions to fully grasp the phylogenetic distribution and role played by small molecules during this ancient plant symbiosis. This article is part of the theme issue 'The evolution of plant metabolism'.

Evolution of plant metabolism: the state-of-the-art

Immense chemical diversity is one of the hallmark features of plants. This chemo-diversity is mainly underpinned by a highly complex and biodiverse biochemical machinery. Plant metabolic enzymes originated and were inherited from their eukaryotic and prokaryotic ancestors and further diversified by the unprecedentedly high rates of gene duplication and functionalization experienced in land plants. Unlike prokaryotic microbes, which display frequent horizontal gene transfer events and multiple inputs of energy and organic carbon, land plants predominantly rely on organic carbon generated from CO2 and have experienced relatively few gene transfers during their recent evolutionary history. As such, plant metabolic networks have evolved in a stepwise manner using existing networks as a starting point and under various evolutionary constraints. That said, until recently, the evolution of only a handful of metabolic traits had been extensively investigated and as such, the evolution of metabolism has received a fraction of the attention of, the evolution of development, for example. Advances in metabolomics and next-generation sequencing have, however, recently led to a deeper understanding of how a wide range of plant primary and specialized (secondary) metabolic pathways have evolved both as a consequence of natural selection and of domestication and crop improvement processes. This article is part of the theme issue 'The evolution of plant metabolism'.

The SMXL8-AGL9 module mediates crosstalk between strigolactone and gibberellin to regulate strigolactone-induced anthocyanin biosynthesis in apple

Although the strigolactone (SL) signaling pathway and SL-mediated anthocyanin biosynthesis have been reported, the molecular association between SL signaling and anthocyanin biosynthesis remains unclear. In this study, we identified the SL signal transduction pathway associated with anthocyanin biosynthesis and the crosstalk between gibberellin (GA) and SL signaling in apple (Malus × domestica). ELONGATED HYPOCOTYL5 (HY5) acts as a key node integrating SL signaling and anthocyanin biosynthesis, and the SL-response factor AGAMOUS-LIKE MADS-BOX9 (AGL9) promotes anthocyanin biosynthesis by activating HY5 transcription. The SL signaling repressor SUPPRESSOR OF MAX2 1-LIKE8 (SMXL8) interacts with AGL9 to form a complex that inhibits anthocyanin biosynthesis by downregulating HY5 expression. Moreover, the E3 ubiquitin ligase PROTEOLYSIS1 (PRT1) mediates the ubiquitination-mediated degradation of SMXL8, which is a key part of the SL signal transduction pathway associated with anthocyanin biosynthesis. In addition, the GA signaling repressor REPRESSOR-of-ga1-3-LIKE2a (RGL2a) mediates the crosstalk between GA and SL by disrupting the SMXL8-AGL9 interaction that represses HY5 transcription. Taken together, our study reveals the regulatory mechanism of SL-mediated anthocyanin biosynthesis and uncovers the role of SL-GA crosstalk in regulating anthocyanin biosynthesis in apple.

Exogenous application of the apocarotenoid retinaldehyde negatively regulates auxin-mediated root growth

Root development is essential for plant survival. The lack of carotenoid biosynthesis in the phytoene desaturase 3 (pds3) mutant results in short primary roots (PRs) and reduced lateral root formation. In this study, we showed that short-term inhibition of PDS by fluridone suppresses PR growth in wild type, but to a lesser extent in auxin mutants of Arabidopsis (Arabidopsis thaliana). Such an inhibition of PDS activity increased endogenous indole-3-acetic acid levels, promoted auxin signaling, and partially complemented the PR growth of an auxin-deficient mutant, the YUCCA 3 5 7 8 9 quadruple mutant (yucQ). The exogenous application of retinaldehyde (retinal), an apocarotenoid derived from β-carotene, complemented the fluridone-induced suppression of root growth, as well as the short roots of the pds3 mutant. Retinal also partially complemented the auxin-induced suppression of root growth. These results suggest that retinal may play a role in regulating root growth by modulating endogenous auxin levels.

At the crossroads: strigolactones mediate changes in cytokinin synthesis and signalling in response to nitrogen limitation

Strigolactones (SLs) are key regulators of shoot growth and responses to environmental stimuli. Numerous studies have indicated that nitrogen (N) limitation induces SL biosynthesis, suggesting that SLs may play a pivotal role in coordinating systemic responses to N availability, but this idea has not been clearly demonstrated. Here, we generated triple knockout mutants in the SL synthesis gene TaDWARF17 (TaD17) in bread wheat and investigated their phenotypic and transcriptional responses under N limitation, aiming to elucidate the role of SLs in the adaptation to N limitation. Tad17 mutants display typical SL mutant phenotypes, and fail to adapt their shoot growth appropriately to N. Despite exhibiting an increased tillering phenotype, Tad17 mutants continued to respond to N limitation by reducing tiller number, suggesting that SLs are not the sole regulators of tillering in response to N availability. RNA-seq analysis of basal nodes revealed that the loss of D17 significantly altered the transcriptional response of N-responsive genes, including changes in the expression profiles of key N response master regulators. Crucially, our findings suggest that SLs are required for the transcriptional downregulation of cytokinin (CK) synthesis and signalling in response to N limitation. Collectively, our results suggest that SLs are essential for the appropriate morphological and transcriptional adaptation to N limitation in wheat, and that the repressive effect of SLs on shoot growth is partly mediated by their repression of CK synthesis.

Cytokinin catabolism and transport are involved in strigolactone-modulated rice tiller bud elongation fueled by phosphate and nitrogen supply

Phosphate (P) and nitrogen (N) fertilization affect rice tillering, indicating that P- and N-regulated tiller growth has a crucial effect on grain yield. Cytokinins and strigolactones (SLs) promote and inhibit tiller bud outgrowth, respectively; however, the underlying mechanisms are unclear. In this study, tiller bud outgrowth and cytokinin fractions were evaluated in rice plants fertilized at different levels of P and N. Low phosphate or nitrogen (LP or LN) reduced rice tiller numbers and bud elongation, in line with low cytokinin levels in tiller buds and xylem sap as well as low TCSn:GUS expression, a sensitive cytokinin signal reporter, in the stem base. Furthermore, exogenous cytokinin (6-benzylaminopurin, 6-BA) administration restored bud length and TCSn:GUS activity in LP- and LN-treated plants to similar levels as control plants. The TCSn:GUS activity and tiller bud outgrowth were less affected by LP and LN supplies in SL-synthetic and SL-signaling mutants (d17 and d53) compared to LP- and LN-treated wild-type (WT) plants, indicating that SL modulate tiller bud elongation under LP and LN supplies by reducing the cytokinin levels in tiller buds. OsCKX9 (a cytokinin catabolism gene) transcription in buds and roots was induced by LP, LN supplies and by adding the SL analog GR24. A reduced response of cytokinin fractions to LP and LN supplies was observed in tiller buds and xylem sap of the d53 mutant compared to WT plants. These results suggest that cytokinin catabolism and transport are involved in SL-modulated rice tillering fueled by P and N fertilization.

Strigolactones: A promising tool for nutrient acquisition through arbuscular mycorrhizal fungi symbiosis and abiotic stress tolerance

Strigolactones (SLs) constitute essential phytohormones that control pathogen defense, resilience to phosphate deficiency and abiotic stresses. Furthermore, SLs are released into the soil by roots, especially in conditions in which there is inadequate phosphate or nitrogen available. SLs have the aptitude to stimulate the root parasite plants and symbiotic cooperation with arbuscular mycorrhizal (AM) fungi in rhizosphere. The use of mineral resources, especially phosphorus (P), by host plants is accelerated by AMF, which also improves plant growth and resilience to a series of biotic and abiotic stresses. Thus, these SL treatments that promote rhizobial symbiosis are substitutes for artificial fertilizers and other chemicals, supporting ecologically friendly farming practices. Moreover, SLs have become a fascinating target for abiotic stress adaptation in plants, with an array of uses in sustainable agriculture. In this review, the biological activity has been summarized that SLs as a signaling hormone for AMF symbiosis, nutrient acquisition, and abiotic stress tolerance through interaction with other hormones. Furthermore, the processes behind the alterations in the microbial population caused by SL are clarified, emphasizing the interplay with other signaling mechanisms. This review covers the latest developments in SL studies as well as the properties of SLs on microbial populations, plant hormone transductions, interactions and abiotic stress tolerance.

Regulatory mechanism of strigolactone in tall fescue to low-light stress

Strigolactone (SL), a plant hormone derived from carotenoids, has been recognized for its pivotal role in regulating plant growth. Nevertheless, the influence of SL on tall fescue (Festuca arundinacea) under low-light conditions remains unclear. This study aimed to investigate the impact of SL on various aspects of tall fescue, including its morphological characteristics, photosynthesis, levels of antioxidant and concentrations of SL, under low light intensity (LI). The findings showed that GR24, an artificial analog of SL, positively influenced several parameters of tall fescue under LI. In particular, it enhanced the morphological features such as plant height, leaf width, and biomass, while reducing the number of tillers. Furthermore, it improved the efficiency of photosynthetic by enhancing chlorophyll fluorescence and the gas exchange parameters, mitigating cell damage and improving the contents of antioxidants by increasing the levels of antioxidant enzymes and non-enzymatic antioxidant compounds. Moreover, treatment with SL led to elevated concentrations of this hormone and the levels of gene expression in related pathways. Owing to the immaturity of the genetic transformation system in tall fescue, partial validation through transgenic and mutant materials was obtained using Arabidopsis (Arabidopsis thaliana). These findings demonstrate that SL alleviates the physiological indicators of tall fescue under LI stress and enhances its tolerance to shade. Additionally, it suggests that SL may regulate the shade tolerance of tall fescue through the involvement of FaD14.

Stereospecific reduction of 2'S-configured strigolactones by cowpea OPR3 enzymes

Strigolactones (SLs), plant-derived apocarotenoids, serve dual roles as phytohormones and rhizosphere signaling molecules. While exogenous administration of SLs to plants aids in studying their functions, the metabolic destiny of these administered SLs remains poorly elucidated. Our previous research demonstrated that among synthetic SL GR24 stereoisomers administered to cowpea (Vigna unguiculata), 2'-epi-GR24 undergoes selective reduction at the C-3',4' double bond in its D-ring. In this investigation, we isolated proteins from cowpea roots based on SL reducing activity and identified 12-oxophytodienoate reductase 3 homologs (VuOPR3s) as contributors to this reduction. Enzymatic assays conducted with recombinant proteins revealed that VuOPR3s exhibited a preference for reducing activity toward 2'S-configured SLs, including 2'-epi-GR24. This specificity for 2'S-configured SLs was congruent with that observed for orobanchol produced by cowpea and its stereoisomers. These findings suggest that exogenously administered SLs undergo enzymatic stereoselective reduction, underscoring the importance of considering stereospecificity when interpreting data obtained from SL usage.

The Evaluation of Debranone Series Strigolactone Agonists for Germination Stimulants in Orobanche Species

Strigolactones (SLs) are plant hormones that regulate shoot branching. In addition, SLs act as compounds that stimulate the germination of root parasitic weeds, such as Striga spp. and Orobanche spp., which cause significant damage to agriculture worldwide. Thus, SL agonists have the potential to induce suicidal germination, thereby reducing the seed banks of root parasitic weeds in the soil. Particularly, phenoxyfuranone-type SL agonists, known as debranones, exhibit SL-like activity in rice and Striga hermonthica. However, little is known about their effects on Orobanche spp. In this study, we evaluated the germination-inducing activity of debranones against Orobanche minor. Analysis of structure-activity relationships revealed that debranones with electron-withdrawing substituents at the 2,4- or 2,6-position strongly induced the germination of Orobanche minor. Lastly, biological assays indicated that 5-(2-fluoro-4-nitrophenoxy)-3-methylfuran-2(5H)-one (test compound 61) induced germination to a comparable or even stronger extent than GR24, a well-known synthetic SL. Altogether, our data allowed us to infer that this enhanced activity was due to the recognition of compound 61 by the SLs receptor, KAI 2d, in Orobanche minor.

The Psathyrostachys juncea DWARF27 gene encodes an all-trans-/9-cis-beta-carotene isomerase in the control of plant branches in Arabidopsis thaliana by strigolactones

Strigolactones (SLs), carotenoid-derived plant hormones, govern the growth and development of both monocotyledonous and dicotyledonous plants. DWARF27 (D27), a plastid-targeted protein located at the initiation site of the core pathway in SL synthesis, plays a crucial role in regulating plant tillering (branching). In rice (Oryza sativa) and wheat (Triticum aestivum), OsD27 and TaD27-B proteins modulate the number of plant tillers by participating in SL biosynthesis. Similarly, AtD27 in Arabidopsis thaliana is required for SL production and has a significant impact on phenotypic changes related to branching. At the same time, TaD27 in wheat has been confirmed as a functional orthologue of AtD27 in Arabidopsis, and both Psathyrostachys juncea and wheat belong to the Triticeae, so we speculate that PjD27 gene may also have the same function as AtD27 in Arabidopsis. In this study, we initially screened the PjD27 gene significantly associated with tillering regulation through transcriptome data analysis and subsequently validated its expression levels using qRT-PCR analysis. Furthermore, we conducted phylogenetic analysis using amino acid sequences from 41 species, including P. juncea, to identify closely related species of P. juncea. Here, we analyze the conservation of D27 protein among P. juncea, rice, wheat, and Arabidopsis and provide preliminary evidence suggesting that PjD27 protein is an orthologue of D27 protein in Arabidopsis. Through reverse genetics, we demonstrate the crucial role of PjD27 in regulating plant branching, establishing it as a functional orthologue of D27 in Arabidopsis. Furthermore, following transient expression in tobacco (Nicotiana tabacum), we demonstrate that the subcellular location of the PjD27 protein is consistent with the cellular location of TaD27-B in wheat. Quantitative analysis of SLs shows that PjD27 is a key gene regulating tillering (branching) by participating in SL biosynthesis. By elucidating the function of the PjD27 gene, our findings provide valuable genetic resources for new germplasm creation and improving grain yield in P. juncea.

The lowdown on breakdown: Open questions in plant proteolysis

Proteolysis, including post-translational proteolytic processing as well as protein degradation and amino acid recycling, is an essential component of the growth and development of living organisms. In this article, experts in plant proteolysis pose and discuss compelling open questions in their areas of research. Topics covered include the role of proteolysis in the cell cycle, DNA damage response, mitochondrial function, the generation of N-terminal signals (degrons) that mark many proteins for degradation (N-terminal acetylation, the Arg/N-degron pathway, and the chloroplast N-degron pathway), developmental and metabolic signaling (photomorphogenesis, abscisic acid and strigolactone signaling, sugar metabolism, and postharvest regulation), plant responses to environmental signals (endoplasmic-reticulum-associated degradation, chloroplast-associated degradation, drought tolerance, and the growth-defense trade-off), and the functional diversification of peptidases. We hope these thought-provoking discussions help to stimulate further research.

Strigolactone-induced degradation of SMXL7 and SMXL8 contributes to gibberellin- and auxin-mediated fiber cell elongation in cotton

Cotton (Gossypium) fiber length, a key trait determining fiber yield and quality, is highly regulated by a class of recently identified phytohormones, strigolactones (SLs). However, the underlying molecular mechanisms of SL signaling involved in fiber cell development are largely unknown. Here, we show that the SL signaling repressors MORE AXILLARY GROWTH2-LIKE7 (GhSMXL7) and GhSMXL8 negatively regulate cotton fiber elongation. Specifically, GhSMXL7 and GhSMXL8 inhibit the polyubiquitination and degradation of the gibberellin (GA)-triggered DELLA protein (GhSLR1). Biochemical analysis revealed that GhSMXL7 and GhSMXL8 physically interact with GhSLR1, which interferes with the association of GhSLR1 with the E3 ligase GA INSENSITIVE2 (GhGID2), leading to the repression of GA signal transduction. GhSMXL7 also interacts with the transcription factor GhHOX3, preventing its binding to the promoters of essential fiber elongation regulatory genes. Moreover, both GhSMXL7 and GhSMXL8 directly bind to the promoter regions of the AUXIN RESPONSE FACTOR (ARF) genes GhARF18-10A, GhARF18-10D, and GhARF19-7D to suppress their expression. Cotton plants in which GhARF18-10A, GhARF18-10D, and GhARF19-7D transcript levels had been reduced by virus-induced gene silencing (VIGS) displayed reduced fiber length compared with control plants. Collectively, our findings reveal a mechanism illustrating how SL integrates GA and auxin signaling to coordinately regulate plant cell elongation at the single-cell level.

OsCYP706C2 diverts rice strigolactone biosynthesis to a noncanonical pathway branch

Strigolactones exhibit dual functionality as regulators of plant architecture and signaling molecules in the rhizosphere. The important model crop rice exudes a blend of different strigolactones from its roots. Here, we identify the inaugural noncanonical strigolactone, 4-oxo-methyl carlactonoate (4-oxo-MeCLA), in rice root exudate. Comprehensive, cross-species coexpression analysis allowed us to identify a cytochrome P450, OsCYP706C2, and two methyl transferases as candidate enzymes for this noncanonical rice strigolactone biosynthetic pathway. Heterologous expression in yeast and Nicotiana benthamiana indeed demonstrated the role of these enzymes in the biosynthesis of 4-oxo-MeCLA, which, expectedly, is derived from carlactone as substrate. The oscyp706c2 mutants do not exhibit a tillering phenotype but do have delayed mycorrhizal colonization and altered root phenotype. This work sheds light onto the intricate complexity of strigolactone biosynthesis in rice and delineates its role in symbiosis and development.

Smoke-water treatment of seeds, an ancient technique for increasing seed vigor

Germination is an essential phenomenon in the life cycle of plants, and a variety of external and internal factors influence it. Fire and the produced smoke have been vital environmental stimulants for the germination of seeds in many plant species, like Leucospermum cordifolium and Serruria florida. These plants do not germinate at all if fire and smoke are not present. This phenomenon of germination in plant species has existed in the ecosystem since ancient times. Various studies to study the response of seeds to smoke and its extracts have been undertaken for stimulation of germination by burning various plant materials and bubbling the smoke produced through water. The application of plant-derived smoke and smoke water is well known for promoting germination, breaking dormancy, and checking abiotic stress. This significantly indicates that plant-derived smoke contains some bioactive metabolites responsible for the physiological metabolism of seed germination and is involved in enhancing seed vigor. The present review deals with the ancient use of smoke and smoke extracts for seed priming, the cost-efficient method of its preparation, the mode of action of karrikins relating to its perception by plants, and its significant effects on various crops, including its ability to check biotic and abiotic stresses.

Strigolactones Negatively Regulate Tobacco Mosaic Virus Resistance in Nicotiana benthamiana

Strigolactones (SLs) are plant hormones that regulate diverse developmental processes and environmental responses in plants. It has been discovered that SLs play an important role in regulating plant immune resistance to pathogens but there are currently no reports on their role in the interaction between Nicotiana benthamiana and the tobacco mosaic virus (TMV). In this study, the exogenous application of SLs weakened the resistance of N. benthamiana to TMV, promoting TMV infection, whereas the exogenous application of Tis108, a SL inhibitor, resulted in the opposite effect. Virus-induced gene silencing (VIGS) inhibition of two key SL synthesis enzyme genes, NtCCD7 and NtCCD8, enhanced the resistance of N. benthamiana to TMV. Additionally, we conducted a screening of N. benthamiana related to TMV infection. TMV-infected plants treated with SLs were compared to the control by using RNA-seq. The KEGG enrichment analysis and weighted gene co-expression network analysis (WGCNA) of differentially expressed genes (DEGs) suggested that plant hormone signaling transduction may play a significant role in the SL-TMV-N. benthamiana interactions. This study reveals new functions of SLs in regulating plant immunity and provides a reference for controlling TMV diseases in production.

Structural insights into strigolactone catabolism by carboxylesterases reveal a conserved conformational regulation

Phytohormone levels are regulated through specialized enzymes, participating not only in their biosynthesis but also in post-signaling processes for signal inactivation and cue depletion. Arabidopsis thaliana (At) carboxylesterase 15 (CXE15) and carboxylesterase 20 (CXE20) have been shown to deplete strigolactones (SLs) that coordinate various growth and developmental processes and function as signaling molecules in the rhizosphere. Here, we elucidate the X-ray crystal structures of AtCXE15 (both apo and SL intermediate bound) and AtCXE20, revealing insights into the mechanisms of SL binding and catabolism. The N-terminal regions of CXE15 and CXE20 exhibit distinct secondary structures, with CXE15 characterized by an alpha helix and CXE20 by an alpha/beta fold. These structural differences play pivotal roles in regulating variable SL hydrolysis rates. Our findings, both in vitro and in planta, indicate that a transition of the N-terminal helix domain of CXE15 between open and closed forms facilitates robust SL hydrolysis. The results not only illuminate the distinctive process of phytohormone breakdown but also uncover a molecular architecture and mode of plasticity within a specific class of carboxylesterases.

Distinguishing the functions of canonical strigolactones as rhizospheric signals

Strigolactones (SLs) act as regulators of plant architecture as well as signals in rhizospheric communications. Reduced availability of minerals, particularly phosphorus, leads to an increase in the formation and release of SLs that enable adaptation of root and shoot architecture to nutrient limitation and, simultaneously, attract arbuscular mycorrhizal fungi (AMF) for establishing beneficial symbiosis. Based on their chemical structure, SLs are designated as either canonical or non-canonical; however, the question of whether the two classes are also distinguished in their biological functions remained largely elusive until recently. In this review we summarize the latest advances in SL biosynthesis and highlight new findings pointing to rhizospheric signaling as the major function of canonical SLs.

Genome-Wide Identification and Expression Characterization of the D27 Gene Family of Capsicum annuum L

As a crucial member of the gene family involved in the biosynthesis of strigolactones, D27 plays an important regulatory role in plant branching and root development, which is essential for field management and yield increase in peppers (Capsicum annuum L.). To comprehensively understand the characteristics of the pepper D27 gene family, we identified three CaD27 genes. By analyzing their physicochemical properties, phylogenetic relationships, gene structures, promoters, and expression patterns in different tissues, the characteristics of the CaD27 gene family were revealed. The research results showed that these three CaD27 genes are located in three different chromosomes. Evolutionary analysis divided the members of CaD27 into three groups, and gene collinearity analysis did not find any duplicates, indicating the diversity and non-redundancy of the CaD27 gene family members. In addition, we identified and classified cis-elements in the promoter regions of CaD27 genes, with a relatively high proportion related to light and plant hormone responses. Expression pattern analysis showed that CaD27.1 is expressed in leaves, while CaD27.2 is expressed in roots, indicating tissue specificity. Furthermore, protein interaction predictions revealed an interaction between D27.2 and CCD7. This study provided important insights into the function and regulatory mechanisms of the CaD27 gene family and the role of strigolactones in plant growth and development.

GhMAX2 Contributes to Auxin-Mediated Fiber Elongation in Cotton (Gossypium hirsutum)

Strigolactones (SLs) represent a new group of phytohormones that play a pivotal role in the regulation of plant shoot branching and the development of adventitious roots. In cotton (Gossypium hirsutum, Gh), SLs play a crucial role in the regulation of fiber cell elongation and secondary cell wall thickness. However, the underlying molecular mechanisms of SL signaling involved in fiber cell development are largely unknown. In this study, we report two SL-signaling genes, GhMAX2-3 and GhMAX2-6, which positively regulate cotton fiber elongation. Further protein-protein interaction and degradation assays showed that the repressor of the auxin cascade GhIAA17 serves as a substrate for the F-box E3 ligase GhMAX2. The in vivo ubiquitination assay suggested that GhMAX2-3 and GhMAX2-6 ubiquitinate GhIAA17 and coordinately degrade GhIAA17 with GhTIR1. The findings of this investigation offer valuable insights into the roles of GhMAX2-mediated SL signaling in cotton and establish a solid foundation for future endeavors aimed at optimizing cotton plant cultivation.

Exploring silique number in Brassica napus L.: Genetic and molecular advances for improving yield

Silique number is a crucial yield-related trait for the genetic enhancement of rapeseed (Brassica napus L.). The intricate molecular process governing the regulation of silique number involves various factors. Despite advancements in understanding the mechanisms regulating silique number in Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa), the molecular processes involved in controlling silique number in rapeseed remain largely unexplored. In this review, we identify candidate genes and review the roles of genes and environmental factors in regulating rapeseed silique number. We use genetic regulatory networks for silique number in Arabidopsis and grain number in rice to uncover possible regulatory pathways and molecular mechanisms involved in regulating genes associated with rapeseed silique number. A better understanding of the genetic network regulating silique number in rapeseed will provide a theoretical basis for the genetic improvement of this trait and genetic resources for the molecular breeding of high-yielding rapeseed.

Overexpression of CsBRC, an F-box gene from Camellia sinensis, increased the plant branching in tobacco and rice

Tea plant (Camellia sinensis [L.]) is one of the most important crops in China, and tea branch is an important agronomic trait that determines the yield of tea plant. In previous work focused on GWAS that detecting GWAS signals related to plant architecture through whole genome re-sequencing of ancient tea plants, a gene locus TEA 029928 significantly related to plant type was found. Sequence alignment results showed that this gene belonged to the F-box family. We named it CsBRC. CsBRC-GFP fusion proteins were mainly localized in the plasma membrane. By comparing the phenotypes of CsBRC transgenic tobacco and WT tobacco, it was found that the number of branches of transgenic tobacco was significantly higher than that of wild-type tobacco. Through RNA-seq analysis, it was found that CsBRC affects the branching development of plants by regulating the expression of genes related to brassinosteroid synthesis pathway in plants. In addition, overexpression of CsBRC in rice could increase tiller number, grain length and width, and 1,000-grain weight.

Zaxinone Synthase overexpression modulates rice physiology and metabolism, enhancing nutrient uptake, growth and productivity

The rice Zaxinone Synthase (ZAS) gene encodes a carotenoid cleavage dioxygenase (CCD) that forms the apocarotenoid growth regulator zaxinone in vitro. Here, we generated and characterized constitutive ZAS-overexpressing rice lines, to better understand ZAS role in determining zaxinone content and regulating growth and architecture. ZAS overexpression enhanced endogenous zaxinone level, promoted root growth and increased the number of productive tillers, leading to about 30% higher grain yield per plant. Hormone analysis revealed a decrease in strigolactone (SL) content, which we confirmed by rescuing the high-tillering phenotype through application of a SL analogue. Metabolomics analysis revealed that ZAS overexpressing plants accumulate higher amounts of monosaccharide sugars, in line with transcriptome analysis. Moreover, transgenic plants showed higher carbon (C) assimilation rate and elevated root phosphate, nitrate and sulphate level, enhancing the tolerance towards low phosphate (Pi). Our study confirms ZAS as an important determinant of rice growth and architecture and shows that ZAS regulates hormone homoeostasis and a combination of physiological processes to promote growth and grain yield, which makes this gene an excellent candidate for sustainable crop improvement.

Insights into stereoselective ring formation in canonical strigolactone: Identification of a dirigent domain-containing enzyme catalyzing orobanchol synthesis

Strigolactones (SLs) are plant apocarotenoids with diverse roles and structures. Canonical SLs, widespread and characterized by structural variations in their tricyclic lactone (ABC-ring), are classified into two types based on C-ring configurations. The steric C-ring configuration emerges during the BC-ring closure, downstream of the biosynthetic intermediate, carlactonoic acid (CLA). Most plants produce either type of canonical SLs stereoselectively, e.g., tomato (Solanum lycopersicum) yields orobanchol with an α-oriented C-ring. The mechanisms driving SL structural diversification are partially understood, with limited insight into functional implications. Furthermore, the exact molecular mechanism for the stereoselective BC-ring closure reaction is yet to be known. We identified an enzyme, the stereoselective BC-ring-forming factor (SRF), from the dirigent protein (DIR) family, specifically the DIR-f subfamily, whose biochemical function had not been characterized, making it a key enzyme in stereoselective canonical SL biosynthesis with the α-oriented C-ring. We first confirm the precise catalytic function of the tomato cytochrome P450 SlCYP722C, previously shown to be involved in orobanchol biosynthesis [T. Wakabayashi et al., Sci. Adv. 5, eaax9067 (2019)], to convert CLA to 18-oxocarlactonoic acid. We then show that SRF catalyzes the stereoselective BC-ring closure reaction of 18-oxocarlactonoic acid, forming orobanchol. Our methodology combines experimental and computational techniques, including SRF structure prediction and conducting molecular dynamics simulations, suggesting a catalytic mechanism based on the conrotatory 4π-electrocyclic reaction for the stereoselective BC-ring formation in orobanchol. This study sheds light on the molecular basis of how plants produce SLs with specific stereochemistry in a controlled manner.

Chemistry of Strigolactones, Key Players in Plant Communication

Today, the use of artificial pesticides is questionable and the adaptation to global warming is a necessity. The promotion of favorable natural interactions in the rhizosphere offers interesting perspectives for changing the type of agriculture. Strigolactones (SLs), the latest class of phytohormones to be discovered, are also chemical mediators in the rhizosphere. We present in this review the diversity of natural SLs, their analogs, mimics, and probes essential for the biological studies of this class of compounds. Their biosynthesis and access by organic synthesis are highlighted especially concerning noncanonical SLs, the more recently discovered natural SLs. Organic synthesis of analogs, stable isotope-labeled standards, mimics, and probes are also reviewed here. In the last part, the knowledge about the SL perception is described as well as the different inhibitors of SL receptors that have been developed.

Strigolactone insensitivity affects differential shoot and root transcriptome in barley

Strigolactones (SLs) are plant hormones that play a crucial role in regulating various aspects of plant architecture, such as shoot and root branching. However, the knowledge of SL-responsive genes and transcription factors (TFs) that control the shaping of plant architecture remains elusive. Here, transcriptomic analysis was conducted using the SL-insensitive barley mutant hvd14.d (carried mutation in SL receptor DWARF14, HvD14) and its wild-type (WT) to unravel the differences in gene expression separately in root and shoot tissues. This approach enabled us to select more than six thousand SL-dependent genes that were exclusive to each studied organ or not tissue-specific. The data obtained, along with in silico analyses, found several TFs that exhibited changed expression between the analyzed genotypes and that recognized binding sites in promoters of other identified differentially expressed genes (DEGs). In total, 28 TFs that recognize motifs over-represented in DEG promoters were identified. Moreover, nearly half of the identified TFs were connected in a single network of known and predicted interactions, highlighting the complexity and multidimensionality of SL-related signalling in barley. Finally, the SL control on the expression of one of the identified TFs in HvD14- and dose-dependent manners was proved. Obtained results bring us closer to understanding the signalling pathways regulating SL-dependent plant development.

In vitro assay and inhibition of 9-cis-epoxycarotenoid dioxygenase (NCED) from Solanum lycopersicum and Zea mays

The article reports methods for the expression and assay of 9-cis-epoxycarotenoid cleavage dioxygenase (NCED), an enzyme involved in the biosynthesis of phytohormone abscisic acid in plants. A method for the preparation of the unstable substrate 9'-cis-neoxanthin from fresh spinach is described. The inhibition of Solanum lycopersicum NCED by a series of aryl hydroxamic acid inhibitors is illustrated, and inhibitors D2 and D4 are assayed against NCED isozymes from Zea mays.

Tomato Mutants Reveal Root and Shoot Strigolactone Involvement in Branching and Broomrape Resistance

The phytohormones strigolactones (SLs) control root and shoot branching and are exuded from roots into the rhizosphere to stimulate interaction with mycorrhizal fungi. The exuded SLs serve as signaling molecules for the germination of parasitic plants. The broomrape Phelipanche aegyptiaca is a widespread noxious weed in various crop plants, including tomato (Solanum lycopersicum). We have isolated three mutants that impair SL functioning in the tomato variety M82: SHOOT BRANCHING 1 (sb1) and SHOOT BRANCHING 2 (sb2), which abolish SL biosynthesis, and SHOOT BRANCHING 3 (sb3), which impairs SL perception. The over-branching phenotype of the sb mutants resulted in a severe yield loss. The isogenic property of the mutations in a determinate growth variety enabled the quantitative evaluation of the contribution of SL to yield under field conditions. As expected, the mutants sb1 and sb2 were completely resistant to infection by P. aegyptiaca due to the lack of SL in the roots. In contrast, sb3 was more susceptible to P. aegyptiaca than the wild-type M82. The SL concentration in roots of the sb3 was two-fold higher than in the wild type due to the upregulation of the transcription of SL biosynthesis genes. This phenomenon suggests that the steady-state level of root SLs is regulated by a feedback mechanism that involves the SL signaling pathway. Surprisingly, grafting wild-type varieties on sb1 and sb2 rootstocks eliminated the branching phenotype and yield loss, indicating that SL synthesized in the shoots is sufficient to control shoot branching. Moreover, commercial tomato varieties grafted on sb1 were protected from P. aegyptiaca infection without significant yield loss, offering a practical solution to the broomrape crisis.

Independent regulation of strigolactones and blumenols during arbuscular mycorrhizal symbiosis in rice

The apocarotenoid strigolactones (SLs) facilitate pre-symbiotic communication between arbuscular mycorrhizal (AM) fungi and plants. Related blumenol-C-glucosides (blumenols), have also been associated with symbiosis, but the cues that are involved in the regulation of blumenol accumulation during AM symbiosis remain unclear. In rice, our analyses demonstrated a strict correlation between foliar blumenol abundance and intraradical fungal colonisation. More specifically, rice mutants affected at distinct stages of the interaction revealed that fungal cortex invasion was required for foliar blumenol accumulation. Plant phosphate status and D14L hormone signalling had no effect, contrasting their known role in induction of SLs. This a proportion of the SL biosynthetic enzymes, D27 and D17, are equally required for blumenol production. These results importantly clarify that, while there is a partially shared biosynthetic pathway between SL and blumenols, the dedicated induction of the related apocarotenoids occurs in response to cues acting at distinct stages during the root colonisation process. However, we reveal that neither SLs nor blumenols are essential for fungal invasion of rice roots.

Synthesis and Biological Properties of Fluorescent Strigolactone Mimics Derived from 1,8-Naphthalimide

Strigolactones (SLs) have potential to be used in sustainable agriculture to mitigate various stresses that plants have to deal with. The natural SLs, as well as the synthetic analogs, are difficult to obtain in sufficient amounts for practical applications. At the same time, fluorescent SLs would be useful for the mechanistic understanding of their effects based on bio-imaging or spectroscopic techniques. In this study, new fluorescent SL mimics containing a substituted 1,8-naphthalimide ring system connected through an ether link to a bioactive furan-2-one moiety were prepared. The structural, spectroscopic, and biological activity of the new SL mimics on phytopathogens were investigated and compared with previously synthetized fluorescent SL mimics. The chemical group at the C-6 position of the naphthalimide ring influences the fluorescence parameters. All SL mimics showed effects similar to GR24 on phytopathogens, indicating their suitability for practical applications. The pattern of the biological activity depended on the fungal species, SL mimic and concentration, and hyphal order. This dependence is probably related to the specificity of each fungal receptor-SL mimic interaction, which will have to be analyzed in-depth. Based on the biological properties and spectroscopic particularities, one SL mimic could be a good candidate for microscopic and spectroscopic investigations.

Temperature Effect on Rhizome Development in Perennial rice

Traditional agriculture is becoming increasingly not adapted to global climate change. Compared with annual rice, perennial rice has strong environmental adaptation and needs fewer natural resources and labor inputs. Rhizome, a kind of underground stem for rice to achieve perenniallity, can grow underground horizontally and then bend upward, developing into aerial stems. The temperature has a great influence on plant development. To date, the effect of temperature on rhizome development is still unknown. Fine temperature treatment of Oryza longistaminata (OL) proved that compared with higher temperatures (28-30 ℃), lower temperature (17-19 ℃) could promote the sprouting of axillary buds and enhance negative gravitropism of branches, resulting in shorter rhizomes. The upward growth of branches was earlier at low temperature than that at high temperature, leading to a high frequency of shorter rhizomes and smaller branch angles. Comparative transcriptome showed that plant hormones played an essential role in the response of OL to temperature. The expressions of ARF17, ARF25 and FucT were up-regulated at low temperature, resulting in prospectively asymmetric auxin distribution, which subsequently induced asymmetric expression of IAA20 and WOX11 between the upper and lower side of the rhizome, further leading to upward growth of the rhizome. Cytokinin and auxin are phytohormones that can promote and inhibit bud outgrowth, respectively. The auxin biosynthesis gene YUCCA1 and cytokinin oxidase/dehydrogenase gene CKX4 and CKX9 were up-regulated, while cytokinin biosynthesis gene IPT4 was down-regulated at high temperature. Moreover, the D3 and D14 in strigolactones pathways, negatively regulating bud outgrowth, were up-regulated at high temperature. These results indicated that cytokinin, auxins, and strigolactones jointly control bud outgrowth at different temperatures. Our research revealed that the outgrowth of axillary bud and the upward growth of OL rhizome were earlier at lower temperature, providing clues for understanding the rhizome growth habit under different temperatures, which would be helpful for cultivating perennial rice.

Advances in the Modulation of Potato Tuber Dormancy and Sprouting

The post-harvest phase of potato tuber dormancy and sprouting are essential in determining the economic value. The intricate transition from dormancy to active growth is influenced by multiple factors, including environmental factors, carbohydrate metabolism, and hormonal regulation. Well-established environmental factors such as temperature, humidity, and light play pivotal roles in these processes. However, recent research has expanded our understanding to encompass other novel influences such as magnetic fields, cold plasma treatment, and UV-C irradiation. Hormones like abscisic acid (ABA), gibberellic acid (GA), cytokinins (CK), auxin, and ethylene (ETH) act as crucial messengers, while brassinosteroids (BRs) have emerged as key modulators of potato tuber sprouting. In addition, jasmonates (JAs), strigolactones (SLs), and salicylic acid (SA) also regulate potato dormancy and sprouting. This review article delves into the intricate study of potato dormancy and sprouting, emphasizing the impact of environmental conditions, carbohydrate metabolism, and hormonal regulation. It explores how various environmental factors affect dormancy and sprouting processes. Additionally, it highlights the role of carbohydrates in potato tuber sprouting and the intricate hormonal interplay, particularly the role of BRs. This review underscores the complexity of these interactions and their importance in optimizing potato dormancy and sprouting for agricultural practices.

SUPPRESSOR OF MAX2 1-LIKE (SMXL) homologs are MAX2-dependent repressors of Physcomitrium patens growth

SUPPRESSOR OF MAX2 (SMAX)1-LIKE (SMXL) proteins are a plant-specific clade of type I HSP100/Clp-ATPases. SMXL genes are present in virtually all land plant genomes. However, they have mainly been studied in angiosperms. In Arabidopsis (Arabidopsis thaliana), 3 functional SMXL subclades have been identified: SMAX1/SMXL2, SMXL345, and SMXL678. Of these, 2 subclades ensure endogenous phytohormone signal transduction. SMAX1/SMXL2 proteins are involved in KAI2 ligand (KL) signaling, while SMXL678 proteins are involved in strigolactone (SL) signaling. Many questions remain regarding the mode of action of these proteins, as well as their ancestral roles. We addressed these questions by investigating the functions of the 4 SMXL genes in the moss Physcomitrium patens. We demonstrate that PpSMXL proteins are involved in the conserved ancestral MAX2-dependent KL signaling pathway and negatively regulate growth. However, PpSMXL proteins expressed in Arabidopsis cannot replace SMAX1 or SMXL2 function in KL signaling, whereas they can functionally replace SMXL4 and SMXL5 and restore root growth. Therefore, the molecular functions of SMXL proteins are conserved, but their interaction networks are not. Moreover, the PpSMXLC/D clade positively regulates SL signal transduction in P. patens. Overall, our data reveal that SMXL proteins in moss mediate crosstalk between the SL and KL signaling pathways.

Milestones in understanding transport, sensing, and signaling of the plant nutrient phosphorus

As an essential nutrient element, phosphorus (P) is primarily acquired and translocated as inorganic phosphate (Pi) by plant roots. Pi is often sequestered in the soil and becomes limited for plant growth. Plants have developed a sophisticated array of adaptive responses, termed P starvation responses, to cope with P deficiency by improving its external acquisition and internal utilization. Over the past 2 to 3 decades, remarkable progress has been made toward understanding how plants sense and respond to changing environmental P. This review provides an overview of the molecular mechanisms that regulate or coordinate P starvation responses, emphasizing P transport, sensing, and signaling. We present the major players and regulators responsible for Pi uptake and translocation. We then introduce how P is perceived at the root tip, how systemic P signaling is operated, and the mechanisms by which the intracellular P status is sensed and conveyed. Additionally, the recent exciting findings about the influence of P on plant-microbe interactions are highlighted. Finally, the challenges and prospects concerning the interplay between P and other nutrients and strategies to enhance P utilization efficiency are discussed. Insights obtained from this knowledge may guide future research endeavors in sustainable agriculture.

Recent advances in research on phosphate starvation signaling in plants

Phosphorus is indispensable for plant growth and development, with its status crucial for determining crop productivity. Plants have evolved various biochemical, morphological, and developmental responses to thrive under conditions of low P availability, as inorganic phosphate (Pi), the primary form of P uptake, is often insoluble in soils. Over the past 25 years, extensive research has focused on understanding these responses, collectively forming the Pi starvation response system. This effort has not only expanded our knowledge of strategies to cope with Pi starvation (PS) but also confirmed their adaptive significance. Moreover, it has identified and characterized numerous components of the intricate regulatory network governing P homeostasis. This review emphasizes recent advances in PS signaling, particularly highlighting the physiological importance of local PS signaling in inhibiting primary root growth and uncovering the role of TORC1 signaling in this process. Additionally, advancements in understanding shoot-root Pi allocation and a novel technique for studying Pi distribution in plants are discussed. Furthermore, emerging data on the regulation of plant-microorganism interactions by the PS regulatory system, crosstalk between the signaling pathways of phosphate starvation, phytohormones and immunity, and recent studies on natural variation in Pi homeostasis are addressed.

Environmentally adaptive reshaping of plant photomorphogenesis by karrikin and strigolactone signaling

Coordinated morphogenic adaptation of growing plants is critical for their survival and propagation under fluctuating environments. Plant morphogenic responses to light and warm temperatures, termed photomorphogenesis and thermomorphogenesis, respectively, have been extensively studied in recent decades. During photomorphogenesis, plants actively reshape their growth and developmental patterns to cope with changes in light regimes. Accordingly, photomorphogenesis is closely associated with diverse growth hormonal cues. Notably, accumulating evidence indicates that light-directed morphogenesis is profoundly affected by two recently identified phytochemicals, karrikins (KARs) and strigolactones (SLs). KARs and SLs are structurally related butenolides acting as signaling molecules during a variety of developmental steps, including seed germination. Their receptors and signaling mediators have been identified, and associated working mechanisms have been explored using gene-deficient mutants in various plant species. Of particular interest is that the KAR and SL signaling pathways play important roles in environmental responses, among which their linkages with photomorphogenesis are most comprehensively studied during seedling establishment. In this review, we focus on how the phytochemical and light signals converge on the optimization of morphogenic fitness. We also discuss molecular mechanisms underlying the signaling crosstalks with an aim of developing potential ways to improve crop productivity under climate changes.

Rapid in-situ aerobic biodegradation of high salt and oily food waste employing constructed synthetic microbiome

The high salt content of food waste (FW) severely limits microbial physiological activity and reduces its biodegradability. In this study, a salt-tolerant thermophilic bacterial agent that consists of four different substrate degradation functional strains was evaluated for efficient high salt and oily FW in solid-state aerobic biodegradation disposers. The phy-chemical properties, enzyme activities, microbial community structure, and function during the biodegradation process were evaluated under high salt (5%) stress. The results showed that the agent promoted the degradation rate, increased the matrix temperature, decreased the moisture content (MC), and enhanced enzyme activities without putrid smell. High-throughput sequencing indicated community structure succession between different groups and the positive contribution of the inoculated functional strains. During the FW biodegradation process, the Bacillus sp. inoculated was the dominant genus in the agent group. Furthermore, CCA further confirmed the positive effects of the four inoculated strains on high salt and oily FW aerobic biodegradation. Functional prediction and metabolite results both confirmed that the agent was more efficient in carbon, amino acid, and lipid metabolism, which demonstrated that the synthetic microbial consortium holds a potential advantage for efficiency and subsequent resource utilization for organic fertilizer.

Strigolactones affect the yield of Tartary buckwheat by regulating endogenous hormone levels

BACKGROUND

As a newly class of endogenous phytohormones, strigolactones (SLs) regulate crop growth and yield formation by interacting with other hormones. However, the physiological mechanism of SLs affect the yield by regulating the balance of endogenous hormones of Tartary buckwheat is still unclear.

RESULTS

In this study, a 2-year field experiment was conducted on Tartary buckwheat (Jinqiao 2) to study the effects of different concentrations (0, 10, and 20 µmol/L) of artificial synthetic analogs of SLs (rac-GR24) and inhibitor of SL synthesis (Tis-108) on the growth, endogenous-hormone content, and yield of Tartary buckwheat. The main-stem branch number, grain number per plant, grain weight per plant, and yield of Tartary buckwheat continuously decreased with increased rac-GR24 concentration, whereas the main-stem diameter and plant height initially increased and then decreased. Rac-GR24 treatment significantly increased the content of SLs and abscisic acid (ABA) in grains, and it decreased the content of Zeatin (Z) + Zeatin nucleoside (ZR). Conversely, Tis-108 treatment decreased the content of SLs and ABA but increased the content of Z + ZR. Results of correlation analysis showed that the content of ABA and SLs, the ratio of SLs/(Z + ZR), SLs/ABA, and ABA/(Z + ZR) were significantly negatively correlated with the yield of Tartary buckwheat, and that Z + ZR content was significantly positively correlated with the yield. Regression analysis further showed that ABA/ (Z + ZR) can explain 58.4% of the variation in yield.

CONCLUSIONS

In summary, by adjusting the level of endogenous SLs in Tartary buckwheat, the balance of endogenous hormones in grains can be changed, thereby exerting the effect on yield. The results can provide a new agronomic method for the high-yield cultivation of Tartary buckwheat.

Deciphering the differential expression patterns of yield-related negative regulators in hexaploid wheat cultivars and hybrids at different growth stages

BACKGROUND

Hexaploid bread wheat underwent a series of polyploidization events through interspecific hybridizations that conferred adaptive plasticity and resulted in duplication and neofunctionalization of major agronomic genes. The genetic architecture of polyploid wheat not only confers adaptive plasticity but also offers huge genetic diversity. However, the contribution of different gene copies (homeologs) encoded from different subgenomes (A, B, D) at different growth stages remained unexplored.

METHODS

In this study, hybrid of elite cultivars of wheat were developed via reciprocal crosses (cytoplasm swapping) and phenotypically evaluated. We assessed differential expression profiles of yield-related negative regulators in these cultivars and their F1 hybrids and identified various cis-regulatory signatures by employing bioinformatics tools. Furthermore, the preferential expression patterns of the syntenic triads encoded from A, B, and D subgenomes were assessed to decipher their functional redundancy at six different growth stages.

RESULTS

Hybrid progenies showed better heterosis such as up to 17% increase in the average number of grains and up to 50% increase in average thousand grains weight as compared to mid-parents. Based on the expression profiling, our results indicated significant dynamic transcriptional expression patterns, portraying the different homeolog-dominance at the same stage in the different cultivars and their hybrids. Albeit belonging to same syntenic triads, a dynamic trend was observed in the regulatory signatures of these genes that might be influencing their expression profiles.

CONCLUSION

These findings can substantially contribute and provide insights for the selective introduction of better cultivars into traditional and hybrid breeding programs which can be harnessed for the improvement of future wheat.

2-oxoglutarate-dependent dioxygenases and BAHD acyltransferases drive the structural diversification of orobanchol in Fabaceae plants

Strigolactones (SLs), a class of plant apocarotenoids, serve dual roles as rhizosphere-signaling molecules and plant hormones. Orobanchol, a major naturally occurring SL, along with its various derivatives, has been detected in the root exudates of plants of the Fabaceae family. Medicaol, fabacyl acetate, and orobanchyl acetate were identified in the root exudates of barrel medic (Medicago truncatula), pea (Pisum sativum), and cowpea (Vigna unguiculata), respectively. Although the biosynthetic pathway leading to orobanchol production has been elucidated, the biosynthetic pathways of the orobanchol derivatives have not yet been fully elucidated. Here, we report the identification of 2-oxoglutarate-dependent dioxygenases (DOXs) and BAHD acyltransferases responsible for converting orobanchol to these derivatives in Fabaceae plants. First, the metabolic pathways downstream of orobanchol were analyzed using substrate feeding experiments. Prohexadione, an inhibitor of DOX inhibits the conversion of orobanchol to medicaol in barrel medic. The DOX inhibitor also reduced the formation of fabacyl acetate and fabacol, a precursor of fabacyl acetate, in pea. Subsequently, we utilized a dataset based on comparative transcriptome analysis to select a candidate gene encoding DOX for medicaol synthase in barrel medic. Recombinant proteins of the gene converted orobanchol to medicaol. The candidate genes encoding DOX and BAHD acyltransferase for fabacol synthase and fabacol acetyltransferase, respectively, were selected by co-expression analysis in pea. The recombinant proteins of the candidate genes converted orobanchol to fabacol and acetylated fabacol. Furthermore, fabacol acetyltransferase and its homolog in cowpea acetylated orobanchol. The kinetics and substrate specificity analyses revealed high affinity and strict recognition of the substrates of the identified enzymes. These findings shed light on the molecular mechanisms underlying the structural diversity of SLs.

Design, Synthesis, and Bioactivities of N-Heterocyclic Ureas as Strigolactone Response Antagonists against Parasitic-Weed Seed Germination

The pernicious parasitism exhibited by root parasitic weeds such as Orobanche and Striga poses substantial peril to agricultural productivity and global food security. This deleterious phenomenon hinges upon the targeted induction of the signaling molecule strigolactones (SLs). Consequently, the identification of prospective SL antagonists holds significant promise in the realm of mitigating the infection of these pernicious weeds. In this study, we synthesized and characterized D12 based on a potent SL antagonist KK094. In vivo assay results demonstrated that D12 remarkably impedes the germination of Phelipanche aegyptiaca and Striga asiatica seeds, while also alleviating the inhibitory consequence of the SL analogue GR24 on hypocotyl elongation in Arabidopsis thaliana. The docking study and ITC assay indicated that D12 can interact strongly with the SL receptor protein, which may interfere with the binding of SL to the receptor protein as a result. In addition, the results of crop safety assessment tests showed that D12 had no adverse effects on rice seed germination and seedling growth and development. The outcomes obtained from the present study suggested that D12 exhibited promise as a prospective antagonist of SL receptors, thereby displaying substantial efficacy in impeding the seed germination process of root parasitic weeds, providing a promising basis for rational design and development of further Striga-specific herbicides.

Design, Synthesis and Biological Evaluation of Novel Phenyl-Substituted Naphthoic Acid Ethyl Ester Derivatives as Strigolactone Receptor Inhibitor

Strigolactones (SLs) are plant hormones that regulate several key agronomic traits, including shoot branching, leaf senescence, and stress tolerance. The artificial regulation of SL biosynthesis and signaling has been considered as a potent strategy in regulating plant architecture and combatting the infection of parasitic weeds to help improve crop yield. DL1b is a previously reported SL receptor inhibitor molecule that significantly promotes shoot branching. Here, we synthesized 18 novel compounds based on the structure of DL1b. We performed rice tillering activity assay and selected a novel small molecule, C6, as a candidate SL receptor inhibitor. In vitro bioassays demonstrated that C6 possesses various regulatory functions as an SL inhibitor, including inhibiting germination of the root parasitic seeds Phelipanche aegyptiaca, delaying leaf senescence and promoting hypocotyl elongation of Arabidopsis. ITC analysis and molecular docking experiments further confirmed that C6 can interact with SL receptor proteins, thereby interfering with the binding of SL to its receptor. Therefore, C6 is considered a novel SL receptor inhibitor with potential applications in plant architecture control and prevention of root parasitic weed infestation.

Development of a stable genetic transformation system in Erigeron breviscapus: a case study with EbYUC2 in relation to leaf number and flowering time

MAIN CONCLUSION

A stable genetic transformation system for Erigeron breviscapus was developed. We cloned the EbYUC2 gene and genetically transformed it into Arabidopsis thaliana and E. breviscapus. The leaf number, YUC2 gene expression, and the endogenous auxin content in transgenic plants were significantly increased. Erigeron breviscapus is a prescription drug for the clinical treatment of cardiovascular and cerebrovascular diseases. The rosette leaves have the highest content of the major active compound scutellarin and are an important component in the yield of E. breviscapus. However, little is known about the genes related to the leaf number and flowering time of E. breviscapus. In our previous study, we identified three candidate genes related to the leaf number and flowering of E. breviscapus by combining resequencing data and genome-wide association study (GWAS). However, their specific functions remain to be characterized. In this study, we cloned and transformed the previously identified full-length EbYUC2 gene into Arabidopsis thaliana, developed the first stable genetic transformation system for E. breviscapus, and obtained the transgenic plants overexpressing EbYUC2. Compared with wild-type plants, the transgenic plants showed a significant increase in the number of leaves, which was correlated with the increased expression of EbYUC2. Consistently, the endogenous auxin content, particularly indole-3-acetic acid, in transgenic plants was also significantly increased. These results suggest that EbYUC2 may control the leaf number by regulating auxin biosynthesis, thereby laying a foundation for revealing the molecular mechanism governing the leaf number and flowering time of E. breviscapus.

Comparative Transcriptome Analysis Reveals Inhibitory Roles of Strigolactone in Axillary Bud Outgrowth in Ratoon Rice

Axillary bud outgrowth, a key factor in ratoon rice yield formation, is regulated by several phytohormone signals. The regulatory mechanism of key genes underlying ratoon buds in response to phytohormones in ratoon rice has been less reported. In this study, GR24 (a strigolactone analogue) was used to analyze the ratooning characteristics in rice cultivar Huanghuazhan (HHZ). Results show that the elongation of the axillary buds in the first seasonal rice was significantly inhibited and the ratoon rate was reduced at most by up to 40% with GR24 treatment. Compared with the control, a significant reduction in the content of auxin and cytokinin in the second bud from the upper spike could be detected after GR24 treatment, especially 3 days after treatment. Transcriptome analysis suggested that there were at least 742 and 2877 differentially expressed genes (DEGs) within 6 h of GR24 treatment and 12 h of GR24 treatment, respectively. Further bioinformatics analysis revealed that GR24 treatment had a significant effect on the homeostasis and signal transduction of cytokinin and auxin. It is noteworthy that the gene expression levels of OsCKX1, OsCKX2, OsGH3.6, and OsGH3.8, which are involved in cytokinin or auxin metabolism, were enhanced by the 12 h GR24 treatment. Taken overall, this study showed the gene regulatory network of auxin and cytokinin homeostasis to be regulated by strigolactone in the axillary bud outgrowth of ratoon rice, which highlights the importance of these biological pathways in the regulation of axillary bud outgrowth in ratoon rice and would provide theoretical support for the molecular breeding of ratoon rice.

Genome-Wide Association Analysis of Effective Tillers in Rice under Different Nitrogen Gradients

Nitrogen is a crucial element that impacts rice yields, and effective tillering is a significant agronomic characteristic that can influence rice yields. The way that reduced nitrogen affects effective tillering is a complex quantitative trait that is controlled by multiple genes, and its genetic basis requires further exploration. In this study, 469 germplasm varieties were used for a genome-wide association analysis aiming to detect quantitative trait loci (QTL) associated with effective tillering at low (60 kg/hm2) and high (180 kg/hm2) nitrogen levels. QTLs detected over multiple years or under different treatments were scrutinized in this study, and candidate genes were identified through haplotype analysis and spatio-temporal expression patterns. A total of seven genes (NAL1, OsCKX9, Os01g0690800, Os02g0550300, Os02g0550700, Os04g0615700, and Os04g06163000) were pinpointed in these QTL regions, and were considered the most likely candidate genes. These results provide favorable information for the use of auxiliary marker selection in controlling effective tillering in rice for improved yields.

Comprehensive Evolutionary Analysis of the SMXL Gene Family in Rosaceae: Further Insights into Its Origin, Expansion, Diversification, and Role in Regulating Pear Branching

SMXL genes constitute a conserved gene family that is ubiquitous in angiosperms and involved in regulating various plant processes, including branching, leaf elongation, and anthocyanin biosynthesis, but little is known about their molecular functions in pear branching. Here, we performed genome-wide identification and investigation of the SMXL genes in 16 angiosperms and analyzed their phylogenetics, structural features, conserved motifs, and expression patterns. In total, 121 SMXLs genes were identified and were classified into four groups. The number of non-redundant SMXL genes in each species varied from 3 (Amborella trichopoda Baill.) to 18 (Glycine max Merr.) and revealed clear gene expansion events over evolutionary history. All the SMXL genes showed conserved structures, containing no more than two introns. Three-dimensional protein structure prediction revealed distinct structures between but similar structures within groups. A quantitative real-time PCR analysis revealed different expressions of 10 SMXL genes from pear branching induced by fruit-thinning treatment. Overall, our study provides a comprehensive investigation of SMXL genes in the Rosaceae family, especially pear. The results offer a reference for understanding the evolutionary history of SMXL genes and provide excellent candidates for studying fruit tree branching regulation, and in facilitating pear pruning and planting strategies.

Feedback regulation of the isoprenoid pathway by SsdTPS overexpression has the potential to enhance plant tolerance to drought stress

In order to maintain the dynamic physiological balance, plants are compelled to adjust their energy metabolism and signal transduction to cope with the abiotic stresses caused by complex and changeable environments. The diterpenoid natural compound and secondary metabolites, sclareol, derived from Salvia sclarea, has gained significant attention owing to its economic value as a spice material and diverse physiological activities. Here, we focused on the roles and regulatory mechanisms of the sclareol diterpene synthase gene SsdTPS in the resistance of S. sclarea to abiotic stresses. Our results suggested that abiotic stresses could induce the response and upregulation of SsdTPS expression and isoprenoid pathway in S. sclarea. Ectopic expression of SsdTPS conferred drought tolerance in transgenic Arabidopsis, compared with wild-type. Overexpression of SsdTPS enhanced the transcription of ABA signal transduction synthetic regulators and induced the positive feedback upregulating key regulatory genes in the MEP pathway, thereby promoting the increase of ABA content and improving drought tolerance in transgenic plants. In addition, SsdTPS-overexpressed transgenic Arabidopsis improved the responses of stomatal regulatory genes and ROS scavenging enzyme activities and gene expression to drought stress. This promoted the stomatal closure and ROS reduction, thus enhancing water retention capacity and reducing oxidative stress damage. These findings unveil the potentially positive role of SsdTPS in orchestrating multiple regulatory mechanisms and maintaining homeostasis for improved abiotic stress resistance in S. sclarea, providing a novel insight into strategies for promoting drought resistance and cultivating highly tolerant plants.

Strigolactone biosynthesis in rice can occur via a 9-cis-3-OH-10'-apo-β-carotenal intermediate

Strigolactones (SLs) play a crucial role in regulating plant architecture and mediating rhizosphere interactions. They are synthesized from all-trans-β-carotene converted into the intermediate carlactone (CL) via the intermediate 9-cis-β-apo-10'-carotenal. Recent studies indicate that plants can also synthesize 3-OH-CL from all-trans-β-zeaxanthin via the intermediate 9-cis-3-OH-β-apo-10'-carotenal. However, the question of whether plants can form bioactive SLs from 9-cis-3-OH-β-apo-10'-carotenal remains elusive. In this study, we supplied the 13 C-labeled 9-cis-3-OH-β-apo-10'-carotenal to rice seedlings and monitored the synthesis of SLs using liquid chromatography-mass spectrometry (LC-MS) and Striga bioassay. We further validated the biological activity of 9-cis-3-OH-β-apo-10'-carotenal-derived SLs using the ccd7/d17 SL-deficient mutant, which demonstrated increased Striga seed-germinating activity and partial rescue of tiller numbers and plant height. Our results establish 9-cis-3-OH-β-apo-10'-carotenal as a significant SL biosynthetic intermediate with implications for understanding plant hormonal functions and potential applications in agriculture.