Auxin in action: signalling, transport and the control of plant growth and development

Endogenous cAMP elevation in Brassica napus causes changes in phytohormone levels

In higher plants, the regulatory roles of cAMP (cyclic adenosine 3',5'-monophosphate) signaling remain elusive until now. Cellular cAMP levels are generally much lower in higher plants than in animals and transiently elevated for triggering downstream signaling events. Moreover, plant adenylate cyclase (AC) activities are found in different moonlighting multifunctional proteins, which may pose additional complications in distinguishing a specific signaling role for cAMP. Here, we have developed rapeseed (Brassica napus L.) transgenic plants that overexpress an inducible plant-origin AC activity for generating high AC levels much like that in animal cells, which served the genetic model disturbing native cAMP signaling as a whole in plants. We found that overexpression of the soluble AC activity had significant impacts on the contents of indole-3-acetic acid (IAA) and stress phytohormones, i.e. jasmonic acid (JA), abscisic acid (ABA), and salicylic acid (SA) in the transgenic plants. Acute induction of the AC activity caused IAA overaccumulation, and upregulation of TAA1 and CYP83B1 in the IAA biosynthesis pathways, but also simultaneously the hyper-induction of PR4 and KIN2 expression indicating activation of JA and ABA signaling pathways. We observed typical overgrowth phenotypes related to IAA excess in the transgenic plants, including significant increases in plant height, internode length, width of leaf blade, petiole length, root length, and fresh shoot biomass, as well as the precocious seed development, as compared to wild-type plants. In addition, we identified a set of 1465 cAMP-responsive genes (CRGs), which are most significantly enriched in plant hormone signal transduction pathway, and function mainly in relevance to hormonal, abiotic and biotic stress responses, as well as growth and development. Collectively, our results support that cAMP elevation impacts phytohormone homeostasis and signaling, and modulates plant growth and development. We proposed that cAMP signaling may be critical in configuring the coordinated regulation of growth and development in higher plants.

The roles of nitric oxide in improving postharvest fruits quality: Crosstalk with phytohormones

Nowadays, improving the quality of postharvest fruits has become a hot research topic. Nitric oxide (NO) is often regarded as a signaling molecule that delays the postharvest senescence of fruits. Moreover, phytohormones affect the postharvest senescence of fruits. This review mainly describes how NO improves the postharvest quality of fruits by delaying postharvest fruit senescence, mitigating fruit cold damage and controlling postharvest diseases. Furthermore, the crosstalk of NO and multiple plant hormones effectively delays the postharvest senescence of fruits, and the major crosstalk mechanisms include (1) mediating phytohormone signaling. (2) inhibiting ETH production. (3) stimulating antioxidant enzyme activity. (4) decreasing membrane lipid peroxidation. (5) maintaining membrane integrity. (6) inhibiting respiration rate. (7) regulating gene expression related to fruit senescence. This review concluded the roles and mechanisms of NO in delaying postharvest fruit senescence. In addition, the crosstalk mechanisms between NO and various phytohormones on the regulation of postharvest fruit quality are also highlighted, which provides new ideas for the subsequent research.

Space, the final frontier: The spatial component of phytoplankton-bacterial interactions

Microscale interactions between marine phytoplankton and bacteria shape the microenvironment of individual cells, impacting their physiology and ultimately influencing global-scale biogeochemical processes like carbon and nutrient cycling. In dilute environments such as the ocean water column, metabolic exchange between microorganisms likely requires close proximity between partners. However, the biological strategies to achieve this physical proximity remain an understudied aspect of phytoplankton-bacterial associations. Understanding the mechanisms by which these microorganisms establish and sustain spatial relationships and the extent to which spatial proximity is necessary for interactions to occur, is critical to learning how spatial associations influence the ecology of phytoplankton and bacterial communities. Here, we provide an overview of current knowledge on the role of space in shaping interactions among ocean microorganisms, encompassing behavioural and metabolic evidence. We propose that characterising phytoplankton-bacterial interactions from a spatial perspective can contribute to a mechanistic understanding of the establishment and maintenance of these associations and, consequently, an enhanced ability to predict the impact of microscale processes on ecosystem-wide phenomena.

The interplay between extracellular and intercellular auxin signaling in plants

The phytohormone auxin exerts control over remarkable developmental processes in plants. It moves from cell to cell, resulting in the creation of both extracellular auxin and intracellular auxin, which are recognized by distinct auxin receptors. These two auxin signaling systems govern different auxin responses while working together to regulate plant development. In this review, we outline the latest research advancements in unraveling these auxin signaling pathways, encompassing auxin perception and signaling transductions. We emphasize the interaction between extracellular auxin and intercellular auxin, which contributes to the intricate role of auxin in plant development.

How chromatin senses plant hormones

Plant hormones activate receptors, initiating intracellular signaling pathways. Eventually, hormone-specific transcription factors become active in the nucleus, facilitating hormone-induced transcriptional regulation. Chromatin plays a fundamental role in the regulation of transcription, the process by which genetic information encoded in DNA is converted into RNA. The structure of chromatin, a complex of DNA and proteins, directly influences the accessibility of genes to the transcriptional machinery. The different signaling pathways and transcription factors involved in the transmission of information from the receptors to the nucleus have been readily explored, but not so much for the specific mechanisms employed by the cell to ultimately instruct the chromatin changes necessary for a fast and robust transcription activation, specifically for plant hormone responses. In this review, we will focus on the advancements in understanding how chromatin receives plant hormones, facilitating the changes necessary for fast, robust, and specific transcriptional regulation.

Molecular glues and induced proximity: An evolution of tools and discovery

Small molecule molecular glues can nucleate protein complexes and rewire interactomes. Molecular glues are widely used as probes for understanding functional proximity at a systems level, and the potential to instigate event-driven pharmacology has motivated their application as therapeutics. Despite advantages such as cell permeability and the potential for low off-target activity, glues are still rare when compared to canonical inhibitors in therapeutic development. Their often simple structure and specific ability to reshape protein-protein interactions pose several challenges for widespread, designer applications. Molecular glue discovery and design campaigns can find inspiration from the fields of synthetic biology and biophysics to mine chemical libraries for glue-like molecules.

Auxin-mediated stress relaxation in pericycle and endoderm remodeling drives lateral root initiation

Plant development relies on the precise coordination of cell growth, which is influenced by the mechanical constraints imposed by rigid cell walls. The hormone auxin plays a crucial role in regulating this growth by altering the mechanical properties of cell walls. During the postembryonic formation of lateral roots, pericycle cells deep within the main root are triggered by auxin to resume growth and divide to form a new root. This growth involves a complex interplay between auxin, growth, and the resolution of mechanical conflicts with the overlying endodermis. However, the exact mechanisms by which this coordination is achieved are still unknown. Here, we propose a model that integrates tissue mechanics and auxin transport, revealing a connection between the auxin-induced relaxation of mechanical stress in the pericycle and auxin signaling in the endodermis. We show that the endodermis initially limits the growth of pericycle cells, resulting in a modest initial expansion. However, the associated stress relaxation is sufficient to redirect auxin to the overlying endodermis, which then actively accommodates the growth, allowing for the subsequent development of the lateral root. Our model uncovers that increased pericycle turgor and decreased endodermal resistance license expansion of the pericycle and how the topology of the endodermis influences the formation of the new root. These findings highlight the interconnected relationship between mechanics and auxin flow during lateral root initiation, emphasizing the vital role of the endodermis in shaping root development through mechanotransduction and auxin signaling.

Roles of the Arabidopsis KEULE Gene in Postembryonic Development

Cytokinesis in plant cells begins with the fusion of vesicles that transport cell wall materials to the center of the cell division plane, where the cell plate forms and expands radially until it fuses with the parental cell wall. Vesicle fusion is facilitated by trans-SNARE complexes, with assistance from Sec1/Munc18 (SM) proteins. The SNARE protein KNOLLE and the SM protein KEULE are required for membrane fusion at the cell plate. Due to the crucial function of KEULE, all Arabidopsis (Arabidopsis thaliana) keule mutants identified to date are seedling lethal. Here, we identified the Arabidopsis serrata4-1 (sea4-1) and sea4-2 mutants, which carry recessive, hypomorphic alleles of KEULE. Homozygous sea4-1 and sea4-2 plants are viable and fertile but have smaller rosettes and fewer leaves at bolting than the wild type. Their leaves are serrated, small, and wavy, with a complex venation pattern. The mutant leaves also develop necrotic patches and undergo premature senescence. RNA-seq revealed transcriptome changes likely leading to reduced cell wall integrity and an increase in the unfolded protein response. These findings shed light on the roles of KEULE in postembryonic development, particularly in the patterning of rosette leaves and leaf margins.

Single-cell transcriptome atlases of soybean root and mature nodule reveal new regulatory programs that control the nodulation process

The soybean root system is complex. In addition to being composed of various cell types, the soybean root system includes the primary root, the lateral roots, and the nodule, an organ in which mutualistic symbiosis with N-fixing rhizobia occurs. A mature soybean root nodule is characterized by a central infection zone where atmospheric nitrogen is fixed and assimilated by the symbiont, resulting from the close cooperation between the plant cell and the bacteria. To date, the transcriptome of individual cells isolated from developing soybean nodules has been established, but the transcriptomic signatures of cells from the mature soybean nodule have not yet been characterized. Using single-nucleus RNA-seq and Molecular Cartography technologies, we precisely characterized the transcriptomic signature of soybean root and mature nodule cell types and revealed the co-existence of different sub-populations of B. diazoefficiens-infected cells in the mature soybean nodule, including those actively involved in nitrogen fixation and those engaged in senescence. Mining of the single-cell-resolution nodule transcriptome atlas and the associated gene co-expression network confirmed the role of known nodulation-related genes and identified new genes that control the nodulation process. For instance, we functionally characterized the role of GmFWL3, a plasma membrane microdomain-associated protein that controls rhizobial infection. Our study reveals the unique cellular complexity of the mature soybean nodule and helps redefine the concept of cell types when considering the infection zone of the soybean nodule.

Plant-Entomopathogenic Fungi Interaction: Recent Progress and Future Prospects on Endophytism-Mediated Growth Promotion and Biocontrol

Entomopathogenic fungi, often acknowledged primarily for their insecticidal properties, fulfill diverse roles within ecosystems. These roles encompass endophytism, antagonism against plant diseases, promotion of the growth of plants, and inhabitation of the rhizosphere, occurring both naturally and upon artificial inoculation, as substantiated by a growing body of contemporary research. Numerous studies have highlighted the beneficial aspects of endophytic colonization. This review aims to systematically organize information concerning the direct (nutrient acquisition and production of phytohormones) and indirect (resistance induction, antibiotic and secondary metabolite production, siderophore production, and mitigation of abiotic and biotic stresses) implications of endophytic colonization. Furthermore, a thorough discussion of these mechanisms is provided. Several challenges, including isolation complexities, classification of novel strains, and the impact of terrestrial location, vegetation type, and anthropogenic reluctance to use fungal entomopathogens, have been recognized as hurdles. However, recent advancements in biotechnology within microbial research hold promising solutions to many of these challenges. Ultimately, the current constraints delineate potential future avenues for leveraging endophytic fungal entomopathogens as dual microbial control agents.

MtPIN4 plays critical roles in amino acid biosynthesis and metabolism of seed in Medicago truncatula

The regulation of seed development is critical for determining crop yield. Auxins are vital phytohormones that play roles in various aspects of plant growth and development. However, its role in amino acid biosynthesis and metabolism in seeds is not fully understood. In this study, we identified a mutant with small seeds through forward genetic screening in Medicago truncatula. The mutated gene encodes MtPIN4, an ortholog of PIN1. Using molecular approaches and integrative omics analyses, we discovered that auxin and amino acid content significantly decreased in mtpin4 seeds, highlighting the role of MtPIN4-mediated auxin distribution in amino acid biosynthesis and metabolism. Furthermore, genetic analysis revealed that the three orthologs of PIN1 have specific and overlapping functions in various developmental processes in M. truncatula. Our findings emphasize the significance of MtPIN4 in seed development and offer insights into the molecular mechanisms governing the regulation of seed size in crops. This knowledge could be applied to enhance crop quality by targeted manipulation of seed protein regulatory pathways.

Ectopic assembly of an auxin efflux control machinery shifts developmental trajectories

Polar auxin transport in the Arabidopsis (Arabidopsis thaliana) root tip maintains high auxin levels around the stem cell niche that gradually decrease in dividing cells but increase again once they transition toward differentiation. Protophloem differentiates earlier than other proximal tissues and employs a unique auxin "canalization" machinery that is thought to balance auxin efflux with retention. It consists of a proposed activator of PIN-FORMED (PIN) auxin efflux carriers, the cAMP-, cGMP- and Calcium-dependent (AGC) kinase PROTEIN KINASE ASSOCIATED WITH BRX (PAX); its inhibitor, BREVIS RADIX (BRX); and PHOSPHATIDYLINOSITOL-4-PHOSPHATE-5-KINASE (PIP5K) enzymes, which promote polar PAX and BRX localization. Because of a dynamic PAX-BRX-PIP5K interplay, the net cellular output of this machinery remains unclear. In this study, we deciphered the dosage-sensitive regulatory interactions among PAX, BRX, and PIP5K by their ectopic expression in developing xylem vessels. The data suggest that the dominant collective output of the PAX-BRX-PIP5K module is a localized reduction in PIN abundance. This requires PAX-stimulated clathrin-mediated PIN endocytosis upon site-specific phosphorylation, which distinguishes PAX from other AGC kinases. An ectopic assembly of the PAX-BRX-PIP5K module is sufficient to cause cellular auxin retention and affects root growth vigor by accelerating the trajectory of xylem vessel development. Our data thus provide direct evidence that local manipulation of auxin efflux alters the timing of cellular differentiation in the root.

Molecular regulatory mechanisms of staminate strobilus development and dehiscence in Torreya grandis

Gymnosperms are mostly dioecious, and their staminate strobili undergo a longer developmental period than those of angiosperms. However, the underlying molecular mechanisms remain unclear. This study aimed to identify key genes and pathways involved in staminate strobilus development and dehiscence in Torreya grandis. Through weighted gene co-expression network analysis (WGCNA), we identified fast elongation-related genes enriched in carbon metabolism and auxin signal transduction, whereas dehiscence-related genes were abundant in alpha-linolenic acid metabolism and the phenylpropanoid pathway. Based on WGCNA, we also identified PHYTOCHROME-INTERACTING FACTOR4 (TgPIF4) as a potential regulator for fast elongation of staminate strobilus and 2 WRKY proteins (TgWRKY3 and TgWRKY31) as potential regulators for staminate strobilus dehiscence. Multiple protein-DNA interaction analyses showed that TgPIF4 directly activates the expression of TRANSPORT INHIBITOR RESPONSE2 (TgTIR2) and NADP-MALIC ENZYME (TgNADP-ME). Overexpression of TgPIF4 significantly promoted staminate strobilus elongation by elevating auxin signal transduction and pyruvate content. TgWRKY3 and TgWRKY31 bind to the promoters of the lignin biosynthesis gene PHENYLALANINE AMMONIA-LYASE (TgPAL) and jasmonic acid metabolism gene JASMONATE O-METHYLTRANSFERASE (TgJMT), respectively, and directly activate their transcription. Overexpression of TgWRKY3 and TgWRKY31 in the staminate strobilus led to early dehiscence, accompanied by increased lignin and methyl jasmonate levels, respectively. Collectively, our findings offer a perspective for understanding the growth of staminate strobili in gymnosperms.

Targeted protein degradation: from mechanisms to clinic

Targeted protein degradation refers to the use of small molecules to induce the selective degradation of proteins. In its most common form, this degradation is achieved through ligand-mediated neo-interactions between ubiquitin E3 ligases - the principal waste disposal machines of a cell - and the protein targets of interest, resulting in ubiquitylation and subsequent proteasomal degradation. Notable advances have been made in biological and mechanistic understanding of serendipitously discovered degraders. This improved understanding and novel chemistry has not only provided clinical proof of concept for targeted protein degradation but has also led to rapid growth of the field, with dozens of investigational drugs in active clinical trials. Two distinct classes of protein degradation therapeutics are being widely explored: bifunctional PROTACs and molecular glue degraders, both of which have their unique advantages and challenges. Here, we review the current landscape of targeted protein degradation approaches and how they have parallels in biological processes. We also outline the ongoing clinical exploration of novel degraders and provide some perspectives on the directions the field might take.

Investigation into the Synthesis, Bioactivity, and Mechanism of Action of the Novel 6-Pyrazolyl-2-picolinic Acid as a Herbicide

A series of new 4-amino-3,5-dicholo-6-(5-aryl-substituted-1H-pyrazol-1-yl)-2-picolinic acid compounds were designed and prepared to discover herbicidal molecules. The inhibitory activities of all new compounds against the root growth ofArabidopsis thaliana were assayed. On the whole, the new synthesized compounds displayed good inhibition effects and had excellent herbicidal activities on root growth of weed at 500 μM. Importantly, a selection of compounds demonstrated comparable herbicidal properties to picloram. At the dosage of 250 g/ha, most of the compounds showed a 100% postemergence herbicidal activity to control Chenopodium album and Amaranthus retroflexus. Using compound V-2, the mechanism of action was investigated based on a phenotype study using AFB5-deficient Arabidopsis thaliana. It was found that the novel 6-pyrazolyl-2-picolinic acids were auxinic compounds. In addition, it was proposed that V-2 may be an immune activator due to its upregulation of defense genes and the increased content of jasmonic acid.

Auxin regulates bulbil initiation by mediating sucrose metabolism in Lilium lancifolium

Lily bulbils, which serve as advantageous axillary organs for vegetative propagation, have not been extensively studied in terms of the mechanism of bulbil initiation. The functions of auxin and sucrose metabolism have been implicated in axillary organ development, but their relationship in regulating bulbil initiation remains unclear. In this study, exogenous indole-3-acetic acid (IAA) treatment increased the endogenous auxin levels at leaf axils and significantly decreased bulbil number, whereas treatment with the auxin polar transport inhibitor N-1-naphthylphthalamic acid (NPA), which resulted in a low auxin concentration at leaf axils, stimulated bulbil initiation and increased bulbil number. A low level of auxin caused by NPA spraying or silencing of auxin biosynthesis genes YUCCA FLAVIN MONOOXYGENASE-LIKE 6 (LlYUC6) and TRYPTOPHAN AMINOTRANSFERASERELATED 1 (LlTAR1) facilitated sucrose metabolism by activating the expression of SUCROSE SYNTHASES 1 (LlSusy1) and CELL WALL INVERTASE 2 (LlCWIN2), resulting in enhanced bulbil initiation. Silencing LlSusy1 or LlCWIN2 hindered bulbil initiation. Moreover, the transcription factor BASIC HELIX-LOOP-HELIX 35 (LlbHLH35) directly bound the promoter of LlSusy1, but not the promoter of LlCWIN2, and activated its transcription in response to the auxin content, bridging the gap between auxin and sucrose metabolism. In conclusion, our results reveal that an LlbHLH35-LlSusy1 module mediates auxin-regulated sucrose metabolism during bulbil initiation.

Bacterial indole-3-acetic acid: A key regulator for plant growth, plant-microbe interactions, and agricultural adaptive resilience

Indole-3-acetic acid (IAA), a fundamental phytohormone categorized under auxins, not only influences plant growth and development but also plays a critical role in plant-microbe interactions. This study reviews the role of IAA in bacteria-plant communication, with a focus on its biosynthesis, regulation, and the subsequent effects on host plants. Bacteria synthesize IAA through multiple pathways, which include the indole-3-acetamide (IAM), indole-3-pyruvic acid (IPyA), and several other routes, whose full mechanisms remain to be fully elucidated. The production of bacterial IAA affects root architecture, nutrient uptake, and resistance to various abiotic stresses such as drought, salinity, and heavy metal toxicity, enhancing plant resilience and thus offering promising routes to sustainable agriculture. Bacterial IAA synthesis is regulated through complex gene networks responsive to environmental cues, impacting plant hormonal balances and symbiotic relationships. Pathogenic bacteria have adapted mechanisms to manipulate the host's IAA dynamics, influencing disease outcomes. On the other hand, beneficial bacteria utilize IAA to promote plant growth and mitigate abiotic stresses, thereby enhancing nutrient use efficiency and reducing dependency on chemical fertilizers. Advancements in analytical methods, such as liquid chromatography-tandem mass spectrometry, have improved the quantification of bacterial IAA, enabling accurate measurement and analysis. Future research focusing on molecular interactions between IAA-producing bacteria and host plants could facilitate the development of biotechnological applications that integrate beneficial bacteria to improve crop performance, which is essential for addressing the challenges posed by climate change and ensuring global food security. This integration of bacterial IAA producers into agricultural practice promises to revolutionize crop management strategies by enhancing growth, fostering resilience, and reducing environmental impact.

Analysis of the regulatory mechanism of exogenous IAA-mediated tryptophan accumulation and synthesis of endogenous IAA in Chlorococcum humicola

The activated sludge method is widely used for the treatment of phenol-containing wastewater, which gives rise to the problem of toxic residual sludge accumulation. Indole-3-acetic acid (IAA), a typical phytohormone, facilitates the microalgal resistance to toxic inhibition while promoting biomass accumulation. In this study, Chlorococcum humicola (C. humicola) was cultured in toxic sludge extract and different concentrations of IAA were used to regulate its physiological properties and enrichment of high value-added products. Ultimately, proteomics analysis was used to reveal the response mechanism of C. humicola to exogenous IAA. The results showed that the IAA concentration of 5 × 10-6 mol/L (M) was most beneficial for C. humicola to cope with the toxic stress in the sludge extract medium, to promote the activity of rubisco enzyme, to enhance the efficiency of photosynthesis, and, finally, to accumulate protein as a percentage of specific dry weight 1.57 times more than that of the control group. Exogenous IAA altered the relative abundance of various amino acids in C. humicola cells, and proteomic analyses showed that exogenous IAA stimulated the algal cells to produce more indole-3-glycerol phosphate (IGP), indole, and serine by up-regulating the enzymes. These precursors are converted to tryptophan under the regulation of tryptophan synthase (A0A383V983), and tryptophan can be metabolized to endogenous IAA to promote the growth of C. humicola. These findings have important implications for the treatment of toxic residual sludge while enriching for high-value amino acids.

Nodulation Experiment by Cross-Inoculation of Nitrogen-Fixing Bacteria Isolated from Root Nodules of Several Leguminous Plants

Root-nodule nitrogen-fixing bacteria are known for being specific to particular legumes. This study isolated the endophytic root-nodule bacteria from the nodules of legumes and examined them to determine whether they could be used to promote the formation of nodules in other legumes. Forty-six isolates were collected from five leguminous plants and screened for housekeeping (16S rRNA), nitrogen fixation (nifH), and nodulation (nodC) genes. Based on the 16S rRNA gene sequencing and phylogenetic analysis, the bacterial isolates WC15, WC16, WC24, and GM5 were identified as Rhizobium, Sphingomonas, Methylobacterium, and Bradyrhizobium, respectively. The four isolates were found to have the nifH gene, and the study confirmed that one isolate (GM5) had both the nifH and nodC genes. The Salkowski method was used to measure the isolated bacteria for their capacity to produce phytohormone indole acetic acid (IAA). Additional experiments were performed to examine the effect of the isolated bacteria on root morphology and nodulation. Among the four tested isolates, both WC24 and GM5 induced nodulation in Glycine max. The gene expression studies revealed that GM5 had a higher expression of the nifH gene. The existence and expression of the nitrogen-fixing genes implied that the tested strain had the ability to fix the atmospheric nitrogen. These findings demonstrated that a nitrogen-fixing bacterium, Methylobacterium (WC24), isolated from a Trifolium repens, induced the formation of root nodules in non-host leguminous plants (Glycine max). This suggested the potential application of these rhizobia as biofertilizer. Further studies are required to verify the N2-fixing efficiency of the isolates.

Analysis of the global transcriptome and miRNAome associated with seed dormancy during seed maturation in rice (Oryza sativa L. cv. Nipponbare)

BACKGROUND

Seed dormancy is a biological mechanism that prevents germination until favorable conditions for the subsequent generation of plants are encountered. Therefore, this mechanism must be effectively established during seed maturation. Studies investigating the transcriptome and miRNAome of rice embryos and endosperms at various maturation stages to evaluate seed dormancy are limited. This study aimed to compare the transcriptome and miRNAome of rice seeds during seed maturation.

RESULTS

Oryza sativa L. cv. Nipponbare seeds were sampled for embryos and endosperms at three maturation stages: 30, 45, and 60 days after heading (DAH). The pre-harvest sprouting (PHS) assay was conducted to assess the level of dormancy in the seeds at each maturation stage. At 60 DAH, the PHS rate was significantly increased compared to those at 30 and 45 DAH, indicating that the dormancy is broken during the later maturation stage (45 DAH to 60 DAH). However, the largest number of differentially expressed genes (DEGs) and differentially expressed miRNAs (DEmiRs) were identified between 30 and 60 DAH in the embryo and endosperm, implying that the gradual changes in genes and miRNAs from 30 to 60 DAH may play a significant role in breaking seed dormancy. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses confirmed that DEGs related to plant hormones were most abundant in the embryo during 45 DAH to 60 DAH and 30 DAH to 60 DAH transitions. Alternatively, most of the DEGs in the endosperm were related to energy and abiotic stress. MapMan analysis and quantitative real-time polymerase chain reaction identified four newly profiled auxin-related genes (OsSAUR6/12/23/25) and one ethylene-related gene (OsERF087), which may be involved in seed dormancy during maturation. Additionally, miRNA target prediction (psRNATarget) and degradome dataset (TarDB) indicated a potential association between osa-miR531b and ethylene biosynthesis gene (OsACO4), along with osa-miR390-5p and the abscisic acid (ABA) exporter-related gene (OsMATE19) as factors involved in seed dormancy.

CONCLUSIONS

Analysis of the transcriptome and miRNAome of rice embryos and endosperms during seed maturation provided new insights into seed dormancy, particularly its relationship with plant hormones such as ABA, auxin, and ethylene.

Distinct toxic effects, gene expression profiles, and phytohormone responses of Polygonatum cyrtonema exposed to two different antibiotics

The excessive usage of veterinary antibiotics has raised significant concerns regarding their environmental hazard and agricultural impact when entering surface water and soil. Animal waste serves as a primary source of organic fertilizer for intensive large-scale agricultural cultivation, including the widely utilized medicinal and edible plant, Polygonatum cyrtonem. In this study, we employed a novel plant stress tissue culture technology to investigate the toxic effects of tetracycline hydrochloride (TCH) and sulfadiazine (SDZ) on P. cyrtonema. TCH and SDZ exhibited varying degrees of influence on plant growth, photosynthesis, and the reactive oxygen species (ROS) scavenging system. Flavonoid levels increased following exposure to TCH and SDZ. The biosynthesis and signaling pathways of the growth hormones auxin and gibberellic acid were suppressed by both antibiotics, while the salicylic acid-mediated plant stress response was specifically induced in the case of SDZ. Overall, the study unveiled both common and unique responses at physiological, biochemical, and molecular levels in P. cyrtonema following exposure to two distinct types of antibiotics, providing a foundational framework for comprehensively elucidating the precise toxic effects of antibiotics and the versatile adaptive mechanisms in plants.

Aethionema arabicum dimorphic seed trait resetting during transition to seedlings

The transition from germinating seeds to emerging seedlings is one of the most vulnerable plant life cycle stages. Heteromorphic diaspores (seed and fruit dispersal units) are an adaptive bet-hedging strategy to cope with spatiotemporally variable environments. While the roles and mechanisms of seedling traits have been studied in monomorphic species, which produce one type of diaspore, very little is known about seedlings in heteromorphic species. Using the dimorphic diaspore model Aethionema arabicum (Brassicaceae), we identified contrasting mechanisms in the germination responses to different temperatures of the mucilaginous seeds (M+ seed morphs), the dispersed indehiscent fruits (IND fruit morphs), and the bare non-mucilaginous M- seeds obtained from IND fruits by pericarp (fruit coat) removal. What follows the completion of germination is the pre-emergence seedling growth phase, which we investigated by comparative growth assays of early seedlings derived from the M+ seeds, bare M- seeds, and IND fruits. The dimorphic seedlings derived from M+ and M- seeds did not differ in their responses to ambient temperature and water potential. The phenotype of seedlings derived from IND fruits differed in that they had bent hypocotyls and their shoot and root growth was slower, but the biomechanical hypocotyl properties of 15-day-old seedlings did not differ between seedlings derived from germinated M+ seeds, M- seeds, or IND fruits. Comparison of the transcriptomes of the natural dimorphic diaspores, M+ seeds and IND fruits, identified 2,682 differentially expressed genes (DEGs) during late germination. During the subsequent 3 days of seedling pre-emergence growth, the number of DEGs was reduced 10-fold to 277 root DEGs and 16-fold to 164 shoot DEGs. Among the DEGs in early seedlings were hormonal regulators, in particular for auxin, ethylene, and gibberellins. Furthermore, DEGs were identified for water and ion transporters, nitrate transporter and assimilation enzymes, and cell wall remodeling protein genes encoding enzymes targeting xyloglucan and pectin. We conclude that the transcriptomes of seedlings derived from the dimorphic diaspores, M+ seeds and IND fruits, undergo transcriptional resetting during the post-germination pre-emergence growth transition phase from germinated diaspores to growing seedlings.

Dynamic interactions between SPX proteins, the ubiquitination machinery, and signalling molecules for stress adaptation at a whole-plant level

The plant macronutrient phosphorus is a scarce resource and plant-available phosphate is limiting in most soil types. Generally, a gene regulatory module called the phosphate starvation response (PSR) enables efficient phosphate acquisition by roots and translocation to other organs. Plants growing on moderate to nutrient-rich soils need to co-ordinate availability of different nutrients and repress the highly efficient PSR to adjust phosphate acquisition to the availability of other macro- and micronutrients, and in particular nitrogen. PSR repression is mediated by a small family of single SYG1/Pho81/XPR1 (SPX) domain proteins. The SPX domain binds higher order inositol pyrophosphates that signal cellular phosphorus status and modulate SPX protein interaction with PHOSPHATE STARVATION RESPONSE1 (PHR1), the central transcriptional regulator of PSR. Sequestration by SPX repressors restricts PHR1 access to PSR gene promoters. Here we focus on SPX4 that primarily acts in shoots and sequesters many transcription factors other than PHR1 in the cytosol to control processes beyond the classical PSR, such as nitrate, auxin, and jasmonic acid signalling. Unlike SPX1 and SPX2, SPX4 is subject to proteasomal degradation not only by singular E3 ligases, but also by SCF-CRL complexes. Emerging models for these different layers of control and their consequences for plant acclimation to the environment will be discussed.

Unveiling the toxic effects, physiological responses and molecular mechanisms of tobacco (Nicotiana tabacum) in exposure to organic ultraviolet filters

Exposure to organic ultraviolet (UV) filters has raised concerns due to their potential adverse effects on environments. However, their toxic mechanisms on plants remain elusive. In this study, using integrative physiological and transcriptomic approaches we investigated the physiological and molecular responses to three representative UV filters, namely oxybenzone (OBZ), avobenzone (AVB), and octinoxate (OMC), in an agricultural model plant tobacco. The exposure to UV filters disrupts the functionality of photosystem reaction centers and the light-harvesting apparatus. Concurrently, UV filters exert a suppressive effect on the expression of genes encoding Rubisco and Calvin-Benson cycle enzymes, resulting in a decreased efficiency of the Calvin-Benson cycle and consequently hampering the process of photosynthesis. Exposure to UV filters leads to significant generation of reactive oxygen species within tobacco leaves and downregulation of oxidoreductase activities. Moreover, UV filters promote abscisic acid (ABA) accumulation by inducing the expression of ABA biosynthesis genes whereas repress indole-3-acetic acid (IAA) biosynthesis gene expression, which induce leaf yellowing and slow plant growth. In summary, the organic UV filters exert toxic effects on tobacco growth by inhibiting chlorophyll synthesis, photosynthesis, and the Calvin-Benson cycle, while generating excessive reactive oxygen species. This study sheds light on the toxic and tolerance mechanisms of UV filters in agricultural crops.

NnARF17 and NnARF18 from lotus promote root formation and modulate stress tolerance in transgenic Arabidopsis thaliana

Auxin response factors (ARFs) play a crucial role in regulating gene expression within the auxin signal transduction pathway, particularly during adventitious root (AR) formation. In this investigation, we identified full-length sequences for ARF17 and ARF18, encompassing 1,800 and 2,055 bp, encoding 599 and 684 amino acid residues, respectively. Despite exhibiting low sequence homology, the ARF17- and ARF18-encoded proteins displayed significant structural similarity and shared identical motifs. Phylogenetic analysis revealed close relationships between NnARF17 and VvARF17, as well as NnARF18 and BvARF18. Both ARF17 and ARF18 demonstrated responsiveness to exogenous indole-3-acetic acid (IAA), ethephon, and sucrose, exhibiting organ-specific expression patterns. Beyond their role in promoting root development, these ARFs enhanced stem growth and conferred drought tolerance while mitigating waterlogging stress in transgenic Arabidopsis plants. RNA sequencing data indicated upregulation of 51 and 75 genes in ARF17 and ARF18 transgenic plants, respectively, including five and three genes associated with hormone metabolism and responses. Further analysis of transgenic plants revealed a significant decrease in IAA content, accompanied by a marked increase in abscisic acid content under normal growth conditions. Additionally, lotus seedlings treated with IAA exhibited elevated levels of polyphenol oxidase, IAA oxidase, and peroxidase. The consistent modulation of IAA content in both lotus and transgenic plants highlights the pivotal role of IAA in AR formation in lotus seedlings.

TOR in plants: Multidimensional regulators of plant growth and signaling pathways

Target Of Rapamycin (TOR) represents a ubiquitous kinase complex that has emerged as a central regulator of cell growth and metabolism in nearly all eukaryotic organisms. TOR is an evolutionarily conserved protein kinase, functioning as a central signaling hub that integrates diverse internal and external cues to regulate a multitude of biological processes. These processes collectively exert significant influence on plant growth, development, nutrient assimilation, photosynthesis, fruit ripening, and interactions with microorganisms. Within the plant domain, the TOR complex comprises three integral components: TOR, RAPTOR, and LST8. This comprehensive review provides insights into various facets of the TOR protein, encompassing its origin, structure, function, and the regulatory and signaling pathways operative in photosynthetic organisms. Additionally, we explore future perspectives related to this pivotal protein kinase.

"Deciphering the enigmatic role of gamma-aminobutyric acid (GABA) in plants: Synthesis, transport, regulation, signaling, and biological roles in interaction with growth regulators and abiotic stresses."

Gamma-aminobutyric acid (GABA) is an amino acid with a four-carbon structure, widely distributed in various organisms. It exists as a zwitterion, possessing both positive and negative charges, enabling it to interact with other molecules and participate in numerous physiological processes. GABA is widely distributed in various plant cell compartments such as cytoplasm mitochondria, vacuoles, peroxisomes, and plastids. GABA is primarily synthesized from glutamate using glutamate decarboxylase and participates in the GABA shunt within mitochondria, regulating carbon and nitrogen metabolism in plants The transport of GABA is regulated by several intracellular and intercellular transporters such as aluminium-activated malate transporters (ALMTs), GABA transporters (GATs), bidirectional amino acid transporters (BATs), and cationic amino acid transporters (CATs). GABA plays a vital role in cellular transformations, gene expression, cell wall modifications, and signal transduction in plants. Recent research has unveiled the role of GABA as a signaling molecule in plants, regulating stomatal movement and pollen tube growth. This review provides insights into multifaceted impact of GABA on physiological and biochemical traits in plants, including cellular communication, pH regulation, Krebs cycle circumvention, and carbon and nitrogen equilibrium. The review highlights involvement of GABA in improving the antioxidant defense system of plants, mitigating levels of reactive oxygen species under normal and stressed conditions. Moreover, the interplay of GABA with other plant growth regulators (PGRs) have also been explored.

A biostimulant yeast, Hanseniaspora opuntiae, modifies Arabidopsis thaliana root architecture and improves the plant defense response against Botrytis cinerea

MAIN CONCLUSION

The biostimulant Hanseniaspora opuntiae regulates Arabidopsis thaliana root development and resistance to Botrytis cinerea. Beneficial microbes can increase plant nutrient accessibility and uptake, promote abiotic stress tolerance, and enhance disease resistance, while pathogenic microorganisms cause plant disease, affecting cellular homeostasis and leading to cell death in the most critical cases. Commonly, plants use specialized pattern recognition receptors to perceive beneficial or pathogen microorganisms. Although bacteria have been the most studied plant-associated beneficial microbes, the analysis of yeasts is receiving less attention. This study assessed the role of Hanseniaspora opuntiae, a fermentative yeast isolated from cacao musts, during Arabidopsis thaliana growth, development, and defense response to fungal pathogens. We evaluated the A. thaliana-H. opuntiae interaction using direct and indirect in vitro systems. Arabidopsis growth was significantly increased seven days post-inoculation with H. opuntiae during indirect interaction. Moreover, we observed that H. opuntiae cells had a strong auxin-like effect in A. thaliana root development during in vitro interaction. We show that 3-methyl-1-butanol and ethanol are the main volatile compounds produced by H. opuntiae. Subsequently, it was determined that A. thaliana plants inoculated with H. opuntiae have a long-lasting and systemic effect against Botrytis cinerea infection, but independently of auxin, ethylene, salicylic acid, or jasmonic acid pathways. Our results demonstrate that H. opuntiae is an important biostimulant that acts by regulating plant development and pathogen resistance through different hormone-related responses.

Genome-wide identification and expression characterization of the GH3 gene family of tea plant (Camellia sinensis)

To comprehensively understand the characteristics of the GH3 gene family in tea plants (Camellia sinensis), we identified 17 CsGH3 genes and analyzed their physicochemical properties, phylogenetic relationships, gene structures, promoters, and expression patterns in different tissues. The study showed that the 17 CsGH3 genes are distributed on 9 chromosomes, and based on evolutionary analysis, the CsGH3 members were divided into three subgroups. Gene duplication analysis revealed that segmental duplications have a significant impact on the amplification of CsGH3 genes. In addition, we identified and classified cis-elements in the CsGH3 gene promoters and detected elements related to plant hormone responses and non-biotic stress responses. Through expression pattern analysis, we observed tissue-specific expression of CsGH3.3 and CsGH3.10 in flower buds and roots. Moreover, based on predictive analysis of upstream regulatory transcription factors of CsGH3, we identified the potential transcriptional regulatory role of gibberellin response factor CsDELLA in CsGH3.14 and CsGH3.15. In this study, we found that CsGH3 genes are involved in a wide range of activities, such as growth and development, stress response, and transcription. This is the first report on CsGH3 genes and their potential roles in tea plants. In conclusion, these results provide a theoretical basis for elucidating the role of GH3 genes in the development of perennial woody plants and offer new insights into the synergistic effects of multiple hormones on plant growth and development in tea plants.

Enhanced metabolic detoxification is associated with fluroxypyr resistance in Bassia scoparia

Auxin-mimic herbicides chemically mimic the phytohormone indole-3-acetic-acid (IAA). Within the auxin-mimic herbicide class, the herbicide fluroxypyr has been extensively used to control kochia (Bassia scoparia). A 2014 field survey for herbicide resistance in kochia populations across Colorado identified a putative fluroxypyr-resistant (Flur-R) population that was assessed for response to fluroxypyr and dicamba (auxin-mimics), atrazine (photosystem II inhibitor), glyphosate (EPSPS inhibitor), and chlorsulfuron (acetolactate synthase inhibitor). This population was resistant to fluroxypyr and chlorsulfuron but sensitive to glyphosate, atrazine, and dicamba. Subsequent dose-response studies determined that Flur-R was 40 times more resistant to fluroxypyr than a susceptible population (J01-S) collected from the same field survey (LD50 720 and 20 g ae ha-1, respectively). Auxin-responsive gene expression increased following fluroxypyr treatment in Flur-R, J01-S, and in a dicamba-resistant, fluroxypyr-susceptible line 9,425 in an RNA-sequencing experiment. In Flur-R, several transcripts with molecular functions for conjugation and transport were constitutively higher expressed, such as glutathione S-transferases (GSTs), UDP-glucosyl transferase (GT), and ATP binding cassette transporters (ABC transporters). After analyzing metabolic profiles over time, both Flur-R and J01-S rapidly converted [14C]-fluroxypyr ester, the herbicide formulation applied to plants, to [14C]-fluroxypyr acid, the biologically active form of the herbicide, and three unknown metabolites. The formation and flux of these metabolites were faster in Flur-R than J01-S, reducing the concentration of phytotoxic fluroxypyr acid. One unique metabolite was present in Flur-R that was not present in the J01-S metabolic profile. Gene sequence variant analysis specifically for auxin receptor and signaling proteins revealed the absence of non-synonymous mutations affecting auxin signaling and binding in candidate auxin target site genes, further supporting our hypothesis that non-target site metabolic degradation is contributing to fluroxypyr resistance in Flur-R.

Genome-wide identification, characterization, and expression analysis of the sweet potato (Ipomoea batatas [L.] Lam.) ARF, Aux/IAA, GH3, and SAUR gene families

BACKGROUND

Auxins are known to have roles in the tuberization process in sweet potato (Ipomoea batatas [L.] Lam.) and these effects are mediated by various auxin signalling gene families. In this study, an analysis of the sweet potato genome was performed to identify the ARF, Aux/IAA, GH3, and SAUR auxin signalling gene family members in this crop.

RESULTS

A total of 29 ARF, 39 Aux/IAA, 13 GH3, and 200 SAUR sequences were obtained, and their biochemical properties and gene expression profiles were analysed. The sequences were relatively conserved based on exon-intron structure, motif analysis, and phylogenetic tree construction. In silico expression analyses of the genes in fibrous and storage roots indicated that many sequences were not differentially expressed in tuberizing and non-tuberizing roots. However, some ARF, Aux/IAA, and SAUR genes were up-regulated in tuberizing storage roots compared to non-tuberizing fibrous roots while many GH3 genes were down-regulated. Additionally, these genes were expressed in a variety of plant parts, with some genes being highly expressed in shoots, leaves, and stems while others had higher expression in the roots. Some of these genes are up-regulated during the plant's response to various hormone treatments and abiotic stresses. Quantitative RT-PCR confirmation of gene expression was also conducted, and the results were concordant with the in silico analyses. A protein-protein interaction network was predicted for the differentially expressed genes, suggesting that these genes likely form part of a complex regulatory network that controls tuberization. These results confirm those of existing studies that show that auxin signalling genes have numerous roles in sweet potato growth and development.

CONCLUSION

This study provides useful information on the auxin signalling gene families in Ipomoea batatas and suggests putative candidates for further studies on the role of auxin signalling in tuberization and plant development.

Transcriptomics reveals a core transcriptional network of K-type cytoplasmic male sterility microspore abortion in wheat (Triticum aestivum L.)

BACKGROUND

Cytoplasmic male sterility (CMS) plays a crucial role in hybrid production. K-type CMS, a cytoplasmic male sterile line of wheat with the cytoplasms of Aegilops kotschyi, is widely used due to its excellent characteristics of agronomic performance, easy maintenance and easy restoration. However, the mechanism of its pollen abortion is not yet clear.

RESULTS

In this study, wheat K-type CMS MS(KOTS)-90-110 (MS line) and it's fertile near-isogenic line MR (KOTS)-90-110 (MR line) were investigated. Cytological analysis indicated that the anthers of MS line microspore nucleus failed to divide normally into two sperm nucleus and lacked starch in mature pollen grains, and the key abortive period was the uninucleate stage to dinuclear stage. Then, we compared the transcriptome of MS line and MR line anthers at these two stages. 11,360 and 5182 differentially expressed genes (DEGs) were identified between the MS and MR lines in the early uninucleate and binucleate stages, respectively. Based on GO enrichment and KEGG pathways analysis, it was evident that significant transcriptomic differences were "plant hormone signal transduction", "MAPK signaling pathway" and "spliceosome". We identified 17 and 10 DEGs associated with the IAA and ABA signal transduction pathways, respectively. DEGs related to IAA signal transduction pathway were downregulated in the early uninucleate stage of MS line. The expression level of DEGs related to ABA pathway was significantly upregulated in MS line at the binucleate stage compared to MR line. The determination of plant hormone content and qRT-PCR further confirmed that hormone imbalance in MS lines. Meanwhile, 1 and 2 DEGs involved in ABA and Ethylene metabolism were also identified in the MAPK cascade pathway, respectively; the significant up regulation of spliceosome related genes in MS line may be another important factor leading to pollen abortion.

CONCLUSIONS

We proposed a transcriptome-mediated pollen abortion network for K-type CMS in wheat. The main idea is hormone imbalance may be the primary factor, MAPK cascade pathway and alternative splicing (AS) may also play important regulatory roles in this process. These findings provided intriguing insights for the molecular mechanism of microspore abortion in K-type CMS, and also give useful clues to identify the crucial genes of CMS in wheat.

BRIP1 and BRIP2 maintain root meristem by affecting auxin-mediated regulation

MAIN CONCLUSION

This study reveals that mutations in BRIP1/2 subunits of the BAS complex disrupt root meristem development by decreasing PIN genes expression, affecting auxin transport, and downregulating essential root genes PLT. Switch defective/sucrose non-fermentable (SWI/SNF) chromatin remodeling complexes play vital roles in plant development. BRAHMA-interacting proteins1 (BRIP1) and BRIP2 are subunits of BRAHMA (BRM)-associated SWI/SNF complex (BAS) in plants; however, their role and underlying regulatory mechanism in root development are still unknown. Here, we show that brip1 brip2 double mutants have a significantly shortened root meristem and an irregular arrangement in a portion of the root stem cell niche. The mutations in BRIP1 and BRIP2 cause decreased expression of the PIN-FORMED (PIN) genes, which in turn reduces the transport of auxin at the root tip, leading to the disruption of the accurate establishment of normal auxin concentration gradients in the stem cells. Chromatin immunoprecipitation (ChIP) experiments indicated that BRIP1 and BRIP2 directly bind to the PINs. Furthermore, we found a significant down-regulation in the expression of key root development genes, PLETHORA (PLT), in brip1 brip2. The brip1 brip2 plt1 plt2 quadruple mutations do not show further exacerbation in the short-root phenotype compared to plt1 plt2 double mutants. Using a dexamethasone (DEX)-inducible PLT2 transgenic line, we showed that acute overexpression of PLT2 partially rescues root meristem defects of brip1 brip2, suggesting that BRIP1 and BRIP2 act in part through the PLT1/2 pathway. Taken together, our results identify the critical role and the underlying mechanism of BRIP1/2 in maintaining the development of root meristem through the regulation of auxin output and expression of PLTs.

NnWOX1-1, NnWOX4-3, and NnWOX5-1 of lotus (Nelumbo nucifera Gaertn)promote root formation and enhance stress tolerance in transgenic Arabidopsis thaliana

BACKGROUND

Adventitious roots (ARs) represent an important organ system for water and nutrient uptake in lotus plants because of degeneration of the principal root. The WUSCHEL-related homeobox (WOX) gene regulates plant development and growth by affecting the expression of several other genes. In this study, three WOX genes, NnWOX1-1, NnWOX4-3, and NnWOX5-1, were isolated and their functions were assessed in Arabidopsis plants.

RESULTS

The full lengths of NnWOX1-1, NnWOX4-3, and NnWOX5-1 were 1038, 645, and 558 bp, encoding 362, 214, and 185 amino acid residues, respectively. Phylogenetic analysis classified NnWOX1-1 and NnWOX4-3 encoding proteins into one group, and NnWOX5-1 and MnWOX5 encoding proteins exhibited strong genetic relationships. The three genes were induced by sucrose and indoleacetic acid (IAA) and exhibited organ-specific expression characteristics. In addition to improving root growth and salt tolerance, NnWOX1-1 and NnWOX4-3 promoted stem development in transgenic Arabidopsis plants. A total of 751, 594, and 541 genes, including 19, 19, and 13 respective genes related to ethylene and IAA metabolism and responses, were enhanced in NnWOX1-1, NnWOX4-3, and NnWOX5-1 transgenic plants, respectively. Further analysis showed that ethylene production rates in transgenic plants increased, whereas IAA, peroxidase, and lignin content did not significantly change. Exogenous application of ethephon on lotus seedlings promoted AR formation and dramatically increased the fresh and dry weights of the plants.

CONCLUSIONS

NnWOX1-1, NnWOX4-3, and NnWOX5-1 influence root formation, stem development, and stress adaptation in transgenic Arabidopsis plants by affecting the transcription of multiple genes. Among these, changes in gene expression involving ethylene metabolism and responses likely critically affect the development of Arabidopsis plants. In addition, ethylene may represent an important factor affecting AR formation in lotus seedlings.

Substrate recognition and transport mechanism of the PIN-FORMED auxin exporters

Auxins are pivotal plant hormones that regulate plant growth and transmembrane polar auxin transport (PAT) direct patterns of development. The PIN-FORMED (PIN) family of membrane transporters mediate auxin export from the plant cell and play crucial roles in PAT. Here we describe the recently solved structures of PIN transporters, PIN1, PIN3, and PIN8, and also their mechanisms of substrate recognition and transport of auxin. We compare structures of PINs in both inward- and outward-facing conformations, as well as PINs with different binding configurations for auxin. By this comparative analysis, a model emerges for an elevator transport mechanism. Central structural elements necessary for function are identified, and we show that these are shared with other distantly related protein families.

Plasmodesmata callose binding protein 2 contributes to the regulation of cambium/phloem formation and auxin response during the tissue reunion process in incised Arabidopsis stem

Plants are exposed to a variety of biotic and abiotic stresses, including wounding at the stem. The healing process (tissue reunion) begins immediately after stem wounding. The plant hormone auxin plays an important role during tissue reunion. In decapitated stems, auxin transport from the shoot apex is reduced and tissue reunion does not occur but is restored by application of indole-3-acetic acid (IAA). In this study, we found that plasmodesmata callose binding protein 2 (PDCB2) affects the expansion of the cambium/phloem region via changes in auxin response during the process of tissue reunion. PDCB2 was expressed in the cortex and endodermis on the incised side of stems 1-3 days after incision. PDCB2-knockout plants showed reduced callose deposition at plasmodesmata and DR5::GUS activity in the endodermis/cortex in the upper region of the incision accompanied by an increase in size of the cambium/phloem region during tissue reunion. In addition, PIN(PIN-FORMED)3, which is involved in lateral auxin transport, was induced by auxin in the cambium/phloem and endodermis/cortex in the upper part of the incision in wild type, but its expression of PIN3 was decreased in pdcb2 mutant. Our results suggest that PDCB2 contributes to the regulation of cambium/phloem development via auxin response.

Genome-Wide Characterization and Haplotypic Variation Analysis of the YUC Gene Family in Foxtail Millet (Setaria italica)

Panicle development and grain production in crop species are essential breeding characteristics affected by the synthesis of auxin, which is influenced by flavin monooxygenase-encoding genes such as YUC (YUCCA) family members. In this trial, fourteen YUCs were identified and named uniformly in foxtail millet, an ancient crop species cultivated across the world. The phylogenetic analysis revealed that the SiYUCs were clustered into four subgroups; protein motif and gene structure analyses suggested that the closely clustered SiYUC genes were relatively conserved within each subgroup; while genome mapping analysis indicated that the SiYUC genes were unevenly distributed on foxtail millet chromosomes and colinear with other grass species. Transcription analysis revealed that the SiYUC genes differed greatly in expression pattern in different tissues and contained hormonal/light/stress-responding cis-elements. The haplotype characterization of SiYUC genes indicated many superior haplotypes of SiYUCs correlated with higher panicle and grain weight could be favorably selected by breeding. These results will be useful for the further study of the functional characteristics of SiYUC genes, particularly with regard to the marker-assisted pyramiding of beneficial haplotypes in foxtail millet breeding programs.

Fertilization of Microbial Composts: A Technology for Improving Stress Resilience in Plants

Microbial compost plays a crucial role in improving soil health, soil fertility, and plant biomass. These biofertilizers, based on microorganisms, offer numerous benefits such as enhanced nutrient acquisition (N, P, and K), production of hydrogen cyanide (HCN), and control of pathogens through induced systematic resistance. Additionally, they promote the production of phytohormones, siderophore, vitamins, protective enzymes, and antibiotics, further contributing to soil sustainability and optimal agricultural productivity. The escalating generation of organic waste from farm operations poses significant threats to the environment and soil fertility. Simultaneously, the excessive utilization of chemical fertilizers to achieve high crop yields results in detrimental impacts on soil structure and fertility. To address these challenges, a sustainable agriculture system that ensures enhanced soil fertility and minimal ecological impact is imperative. Microbial composts, developed by incorporating characterized plant-growth-promoting bacteria or fungal strains into compost derived from agricultural waste, offer a promising solution. These biofertilizers, with selected microbial strains capable of thriving in compost, offer an eco-friendly, cost-effective, and sustainable alternative for agricultural practices. In this review article, we explore the potential of microbial composts as a viable strategy for improving plant growth and environmental safety. By harnessing the benefits of microorganisms in compost, we can pave the way for sustainable agriculture and foster a healthier relationship between soil, plants, and the environment.

QTL mapping for kernel-related traits in a durum wheat x T. dicoccum segregating population

Durum wheat breeding relies on grain yield improvement to meet its upcoming demand while coping with climate change. Kernel size and shape are the determinants of thousand kernel weight (TKW), which is a key component of grain yield, and the understanding of the genetic control behind these traits supports the progress in yield potential. The present study aimed to dissect the genetic network responsible for kernel size components (length, width, perimeter, and area) and kernel shape traits (width-to-length ratio and formcoefficient) as well as their relationships with kernel weight, plant height, and heading date in durum wheat. Quantitative Trait Locus (QTL) mapping was performed on a segregating population of 110 recombinant inbred lines, derived from a cross between the domesticated emmer wheat accession MG5323 and the durum wheat cv. Latino, evaluated in four different environments. A total of 24 QTLs stable across environments were found and further grouped in nine clusters on chromosomes 2A, 2B, 3A, 3B, 4B, 6B, and 7A. Among them, a QTL cluster on chromosome 4B was associated with kernel size traits and TKW, where the parental MG5323 contributed the favorable alleles, highlighting its potential to improve durum wheat germplasm. The physical positions of the clusters, defined by the projection on the T. durum reference genome, overlapped with already known genes (i.e., BIG GRAIN PROTEIN 1 on chromosome 4B). These results might provide genome-based guidance for the efficient exploitation of emmer wheat diversity in wheat breeding, possibly through yield-related molecular markers.

Vesicle trafficking in rice: too little is known

The vesicle trafficking apparatus is a fundamental machinery to maintain the homeostasis of membrane-enclosed organelles in eukaryotic cells. Thus, it is broadly conserved in eukaryotes including plants. Intensive studies in the model organisms have produced a comprehensive picture of vesicle trafficking in yeast and human. However, with respect to the vesicle trafficking of plants including rice, our understanding of the components and their coordinated regulation is very limited. At present, several vesicle trafficking apparatus components and cargo proteins have been identified and characterized in rice, but there still remain large unknowns concerning the organization and function of the rice vesicle trafficking system. In this review, we outline the main vesicle trafficking pathways of rice based on knowledge obtained in model organisms, and summarize current advances of rice vesicle trafficking. We also propose to develop methodologies applicable to rice and even other crops for further exploring the mysteries of vesicle trafficking in plants.

Cavity and entrance pore development in ant plant hypocotyls

Some genera of Rubiaceae in South-eastern Asia are known as typical ant plants. They have large domatia, which form in well-developed hypocotyls in which ants nest. Previously, cavity formation processes were described; however, these reports were dependent on tissue sections of different individuals of different ages. No continuous time-course analyses were done because cavity formation occurs inside the thick tissues of highly swollen domatia. Here we observed cavity formation processes in ant plants by using X-ray computed tomography (CT) imaging and revealed previously overlooked features of cavity formation. Firstly, the cavity pore occurs at the hypocotyl base in not only gravity-dependent but also basal position-dependent manner. Secondly, the cavity forms prior to the start of short tunnel formation between the cavity and the pore. The cavity axis is parallel to the longitudinal axis of the hypocotyl; however, the short tunnel axis between the pore and cavity depends on gravity. Non-invasive CT scanning is a very powerful method to analyze deeply hidden morphogenic processes in organs.

PIN2/3/4 auxin carriers mediate root growth inhibition under conditions of boron deprivation in Arabidopsis

The mechanistic basis by which boron (B) deprivation inhibits root growth via the mediation of root apical auxin transport and distribution remains elusive. This study showed that B deprivation repressed root growth of wild-type Arabidopsis seedlings, which was related to higher auxin accumulation (observed with DII-VENUS and DR5-GFP lines) in B-deprived roots. Boron deprivation elevated the auxin content in the root apex, coinciding with upregulation of the expression levels of auxin biosynthesis-related genes (TAA1, YUC3, YUC9, and NIT1) in shoots, but not in root apices. Phenotyping experiments using auxin transport-related mutants revealed that the PIN2/3/4 carriers are involved in root growth inhibition caused by B deprivation. B deprivation not only upregulated the transcriptional levels of PIN2/3/4, but also restrained the endocytosis of PIN2/3/4 carriers (observed with PIN-Dendra2 lines), resulting in elevated protein levels of PIN2/3/4 in the plasma membrane. Overall, these results suggest that B deprivation not only enhances auxin biosynthesis in shoots by elevating the expression levels of auxin biosynthesis-related genes but also promotes the polar auxin transport from shoots to roots by upregulating the gene expression levels of PIN2/3/4, as well as restraining the endocytosis of PIN2/3/4 carriers, ultimately resulting in auxin accumulation in root apices and root growth inhibition.

A Comprehensive Review Uncovering the Challenges and Advancements in the In Vitro Propagation of Eucalyptus Plantations

The genus Eucalyptus is a globally captivated source of hardwood and is well known for its medicinal uses. The hybrid and wild species of Eucalyptus are widely used as exotic plantations due to their renowned potential of adapting to various systems and sites, and rapid large-scale propagation of genetically similar plantlets, which further leads to the extensive propagation of this species. Tissue culture plays a crucial role in the preservation, propagation, and genetic improvement of Eucalyptus species. Despite unquestionable progression in biotechnological and tissue culture approaches, the productivity of plantations is still limited, often due to the low efficiency of clonal propagation from cuttings. The obtained F1 hybrids yield high biomass and high-quality low-cost raw material for large-scale production; however, the development of hybrid, clonal multiplication, proliferation, and post-developmental studies are still major concerns. This riveting review describes the problems concerning the in vitro and clonal propagation of Eucalyptus plantation and recent advances in biotechnological and tissue culture practices for massive and rapid micropropagation of Eucalyptus, and it highlights the Eucalyptus germplasm preservation techniques.

AUX1, PIN3, and TAA1 collectively maintain fertility in Arabidopsis

MAIN CONCLUSION

We found that auxin synthesis gene TAA1 and auxin polar transport genes AUX1 and PIN3 collectively maintain fertility and seed size in Arabidopsis. Auxin plays a vital role in plant gametophyte development and embryogenesis. The auxin synthesis gene TAA1 and the auxin polar transport genes AUX1 and PIN3 are expressed during Arabidopsis gametophyte and seed development. However, aux1, pin3, and taa1 single mutants only exhibit mild reproductive defects. We, therefore, generated aux1-T pin3 taa1-k2 and aux1-T pin3-2 taa1-k1 triple mutants by crossing or CRISPR/Cas9 technique. These triple mutants displayed severe reproductive defects with approximately 70% and 77%, respectively, of the siliques failing to elongate after anthesis. Reciprocal crosses and microscopy analyses showed that the development of pollen and ovules in the aux1 pin3 taa1 mutants was normal, whereas the filaments were remarkably short, which might be the cause of the silique sterility. Further analyses indicated that the development and morphology of aux1 pin3 taa1 seeds were normal, but their size was smaller compared with that of the wild type. These results indicate that AUX1, PIN3, and TAA1 act in concert to maintain fertility and seed size in Arabidopsis.

Biosynthetic Pathways and Functions of Indole-3-Acetic Acid in Microorganisms

Indole-3-acetic acid (IAA) belongs to the family of auxin indole derivatives. IAA regulates almost all aspects of plant growth and development, and is one of the most important plant hormones. In microorganisms too, IAA plays an important role in growth, development, and even plant interaction. Therefore, mechanism studies on the biosynthesis and functions of IAA in microorganisms can promote the production and utilization of IAA in agriculture. This mini-review mainly summarizes the biosynthesis pathways that have been reported in microorganisms, including the indole-3-acetamide pathway, indole-3-pyruvate pathway, tryptamine pathway, indole-3-acetonitrile pathway, tryptophan side chain oxidase pathway, and non-tryptophan dependent pathway. Some pathways interact with each other through common key genes to constitute a network of IAA biosynthesis. In addition, functional studies of IAA in microorganisms, divided into three categories, have also been summarized: the effects on microorganisms, the virulence on plants, and the beneficial impacts on plants.

Ginkgo biloba GbbZIP08 transcription factor is involved in the regulation of flavonoid biosynthesis

Ginkgo biloba is the oldest relict plant on Earth and an economic plant resource derived from China. Flavonoids extracted from G. biloba are beneficial to the prevention and treatment of cardiovascular and cerebrovascular diseases. Basic leucine zipper (bZIP) transcription factors (TFs) have been recognized to play important roles in plant secondary metabolism. In this study, GbbZIP08 was isolated and characterized. It encodes a protein containing 154 amino acids, which belongs to hypocotyl 5 in group H of the bZIP family. Tobacco transient expression assay indicated that GbbZIP08 was localized in the plant nucleus. GbbZIP08 overexpression showed that the contents of total flavonoids, kaempferol, and anthocyanin in transgenic tobacco were significantly higher than those in the wild type. Transcriptome sequencing analysis revealed significant upregulation of structural genes in the flavonoid biosynthesis pathway. In addition, phytohormone signal transduction pathways, such as the abscisic acid, salicylic acid, auxin, and jasmonic acid pathways, were enriched with a large number of differentially expressed genes. TFs such as MYB, AP2, WRKY, NAC, bZIP, and bHLH, were also differentially expressed. The above results indicated that GbbZIP08 overexpression promoted flavonoid accumulation and increased the transcription levels of flavonoid-synthesis-related genes in plants.

The consequences of synthetic auxin herbicide on plant-herbivore interactions

Although herbicide drift is a common side effect of herbicide application in agroecosystems, its effects on the ecology and evolution of natural communities are rarely studied. A recent shift to dicamba, a synthetic auxin herbicide known for 'drifting' to nontarget areas, necessitates the examination of drift effects on the plant-insect interactions that drive eco-evo dynamics in weed communities. We review current knowledge of direct effects of synthetic auxin herbicides on plant-insect interactions, focusing on plant herbivory, and discuss potential indirect effects, which are cascading effects on organisms that interact with herbicide-exposed plants. We end by developing a framework for the study of plant-insect interactions given drift, highlighting potential changes to plant developmental timing, resource quantity, quality, and cues.

Living yeast-based biostimulants: different genes for the same results?

Nowadays, many products are available in the plant biostimulants market. Among them, living yeast-based biostimulants are also commercialized. Given the living aspect of these last products, the reproducibility of their effects should be investigated to ensure end-users' confidence. Therefore, this study aimed to compare the effects of a living yeast-based biostimulant between two different soybean cultures. These two cultures named C1 and C2 were conducted on the same variety and soil but in different locations and dates until the VC developmental stage (unifoliate leaves unrolled), with Bradyrhizobium japonicum (control and Bs condition) and with and without biostimulant coating seed treatment. The foliar transcriptomic analysis done first showed a high gene expression difference between the two cultures. Despite this first result, a secondary analysis seemed to show that this biostimulant led to a similar pathway enhancement in plants and with common genes even if the expressed genes were different between the two cultures. The pathways which seem to be reproducibly impacted by this living yeast-based biostimulant are abiotic stress tolerance and cell wall/carbohydrate synthesis. Impacting these pathways may protect the plant from abiotic stresses and maintain a higher level of sugars in plant.

Embryonic abnormalities and genotoxicity induced by 2,4-dichlorophenoxyacetic acid during indirect somatic embryogenesis in Coffea

Indirect somatic embryogenesis (ISE) is a morphogenetic pathway in which somatic cells form callus and, later, somatic embryos (SE). 2,4-dichlorophenoxyacetic acid (2,4-D) is a synthetic auxin that promotes the proliferation and dedifferentiation of somatic cells, inducing the ISE. However, 2,4-D can cause genetic, epigenetic, physiological and morphological disorders, preventing the regeneration and/or resulting abnormal somatic embryos (ASE). We aimed to evaluate the toxic 2,4-D effect during the Coffea arabica and C. canephora ISE, assessing the SE morphology, global 5-methylcytosine levels (5-mC%) and DNA damage. Leaf explants were inoculated in media with different 2,4-D concentrations. After 90 days, the friable calli were transferred to the regeneration medium, and the number of normal and abnormal SE was monthly counted. The increase of the 2,4-D concentration increased the number of responsive explants in both Coffea. At 9.06, 18.08 and 36.24 μM 2,4-D, C. arabica presented the highest values of responsive explants, differing from C. canephora. Normal and abnormal SE regeneration increased in relation to the time and 2,4-D concentration. Global 5-mC% varied at different stages of the ISE in both Coffea. Furthermore, the 2,4-D concentration positively correlated with global 5-mC%, and with the mean number of ASE. All ASE of C. arabica and C. canephora exhibited DNA damage and showed higher global 5-mC%. The allotetraploid C. arabica exhibited greater tolerance to the toxic effect of 2,4-D than the diploid C. canephora. We conclude that synthetic 2,4-D auxin promotes genotoxic and phytotoxic disorders and promotes epigenetic changes during Coffea ISE.

Overexpression of a novel small auxin-up RNA gene, OsSAUR11, enhances rice deep rootedness

BACKGROUND

Deep rooting is an important factor affecting rice drought resistance. However, few genes have been identified to control this trait in rice. Previously, we identified several candidate genes by QTL mapping of the ratio of deep rooting and gene expression analysis in rice.

RESULTS

In the present work, we cloned one of these candidate genes, OsSAUR11, which encodes a small auxin-up RNA (SAUR) protein. Overexpression of OsSAUR11 significantly enhanced the ratio of deep rooting of transgenic rice, but knockout of this gene did not significantly affect deep rooting. The expression of OsSAUR11 in rice root was induced by auxin and drought, and OsSAUR11-GFP was localized both in the plasma membrane and cell nucleus. Through an electrophoretic mobility shift assay and gene expression analysis in transgenic rice, we found that the transcription factor OsbZIP62 can bind to the promoter of OsSAUR11 and promote its expression. A luciferase complementary test showed that OsSAUR11 interacts with the protein phosphatase OsPP36. Additionally, expression of several auxin synthesis and transport genes (e.g., OsYUC5 and OsPIN2) were down-regulated in OsSAUR11-overexpressing rice plants.

CONCLUSIONS

This study revealed a novel gene OsSAUR11 positively regulates deep rooting in rice, which provides an empirical basis for future improvement of rice root architecture and drought resistance.