Local Auxin Biosynthesis Mediates Plant Growth and Development

Actin-bundling protein fimbrin serves as a new auxin biosynthesis orchestrator in Arabidopsis root tips

Plants delicately regulate endogenous auxin levels through the coordination of transport, biosynthesis, and inactivation, which is crucial for growth and development. While it is well-established that the actin cytoskeleton can regulate auxin levels by affecting polar transport, its potential role in auxin biosynthesis has remained largely unexplored. Using LC-MS/MS-based methods combined with fluorescent auxin marker detection, we observed a significant increase in root auxin levels upon deletion of the actin bundling proteins AtFIM4 and AtFIM5. Fluorescent observation, immunoblotting analysis, and biochemical approaches revealed that AtFIM4 and AtFIM5 affect the protein abundance of the key auxin synthesis enzyme YUC8 in roots. AtFIM4 and AtFIM5 regulate the auxin synthesis enzyme YUC8 at the protein level, with its degradation mediated by the 26S proteasome. This regulation modulates auxin synthesis and endogenous auxin levels in roots, consequently impacting root development. Based on these findings, we propose a molecular pathway centered on the 'actin cytoskeleton-26S proteasome-YUC8-auxin' axis that controls auxin levels. Our findings shed light on a new pathway through which plants regulate auxin synthesis. Moreover, this study illuminates a newfound role of the actin cytoskeleton in regulating plant growth and development, particularly through its involvement in maintaining protein homeostasis via the 26S proteasome.

Analysis Transcriptome and Phytohormone Changes Associated with the Allelopathic Effects of Ginseng Hairy Roots Induced by Different-Polarity Ginsenoside Components

The allelopathic autotoxicity of ginsenosides is an important cause of continuous cropping obstacles in ginseng planting. There is no report on the potential molecular mechanism of the correlation between polarity of ginsenoside components and their allelopathic autotoxicity. This study applied a combination of metabolomics and transcriptomics analysis techniques, combined with apparent morphology, physiological indexes, and cell vitality detection of the ginseng hairy roots, through which the molecular mechanism of correlation between polarity and allelopathic autotoxicity of ginsenosides were comprehensively studied. The hairy roots of ginseng presented more severe cell apoptosis under the stress of low-polarity ginsenoside components (ZG70). ZG70 exerted allelopathic autotoxicity by regulating the key enzyme genes of cis-zeatin (cZ) synthesis pathway, indole-3-acetic acid (IAA) synthesis pathway, and jasmonates (JAs) signaling transduction pathway. The common pathway for high-polarity ginsenoside components (ZG50) and ZG70 to induce the development of allelopathic autotoxicity was through the expression of key enzymes in the gibberellin (GA) signal transduction pathway, thereby inhibiting the growth of ginseng hairy roots. cZ, indole-3-acetamid (IAM), gibberellin A1 (GA1), and jasmonoyl-L-isoleucine (JA-ILE) were the key response factors in this process. It could be concluded that the polarity of ginsenoside components were negatively correlated with their allelopathic autotoxicity.

Plant Growth Regulation in Cell and Tissue Culture In Vitro

Precise knowledge of all aspects controlling plant tissue culture and in vitro plant regeneration is crucial for plant biotechnologists and their correlated industry, as there is increasing demand for this scientific knowledge, resulting in more productive and resilient plants in the field. However, the development and application of cell and tissue culture techniques are usually based on empirical studies, although some data-driven models are available. Overall, the success of plant tissue culture is dependent on several factors such as available nutrients, endogenous auxin synthesis, organic compounds, and environment conditions. In this review, the most important aspects are described one by one, with some practical recommendations based on basic research in plant physiology and sharing our practical experience from over 20 years of research in this field. The main aim is to help new plant biotechnologists and increase the impact of the plant tissue culture industry worldwide.

Seed priming with light quality and Cyperus rotundus L. extract modulate the germination and initial growth of Moringa oleifera Lam. seedlings

Abstract Improving plant germination is essential to guarantee better quality seedlings. Thus, this research aimed to evaluate whether the seed priming with light quality (LIQ) and the aqueous extract of Cyperus rotundus (AEC) tuber could modulate the germination and initial growth of Moringa oleifera L. seedlings. The experimental design was a completely randomized in the 4x4 factorial scheme, composed of four LIQ conditions (white, blue, red, and distant red light) and four AEC concentrations (0, 25, 50 and 100%). Seed priming with red light reduced the average emergence time, while blue, red, and extreme red lights associated with 50% of aqueous extract of C. rotundus increased shoot initial length and photosynthetic pigment accumulation. Seed priming with blue light resulted in seedlings with a shorter final shoot length. However, application of 100% of aqueous extract of C. rotundus reversed this. The white light in combination with concentrations of 50 and 100% of AEC promoted a higher relative shoot growth rate of seedlings. The research revealed that seed priming with light quality and aqueous extracts of C. rotundus tubers modulates the germination and initial growth of M. oleifera seedlings. More work needs to be done to determine the responsible compounds in AEC that is responsible for priming growth as phytohormones.

Comparative Transcriptome Analysis Reveals the Underlying Response Mechanism to Salt Stress in Maize Seedling Roots

Crop growth and development can be impeded by salt stress, leading to a significant decline in crop yield and quality. This investigation performed a comparative analysis of the physiological responses of two maize inbred lines, namely L318 (CML115) and L323 (GEMS58), under salt-stress conditions. The results elucidated that CML115 exhibited higher salt tolerance compared with GEMS58. Transcriptome analysis of the root system revealed that DEGs shared by the two inbred lines were significantly enriched in the MAPK signaling pathway-plant and plant hormone signal transduction, which wield an instrumental role in orchestrating the maize response to salt-induced stress. Furthermore, the DEGs' exclusivity to salt-tolerant genotypes was associated with sugar metabolism pathways, and these unique DEGs may account for the disparities in salt tolerance between the two genotypes. Meanwhile, we investigated the dynamic global transcriptome in the root systems of seedlings at five time points after salt treatment and compared transcriptome data from different genotypes to examine the similarities and differences in salt tolerance mechanisms of different germplasms.

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.

Gibberellin biosynthesis is required for CPPU-induced parthenocarpy in melon

Spraying N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU), an exogenous cytokinin (CK) growth regulator, is the conventional method for inducing fruit set during melon (Cucumis melo L.) production; however, the mechanism by which CPPU induces fruit set is unclear. Through histological and morphological observations, fruit size was comparable between CPPU-induced fruits and normal pollinated fruits because CPPU-induced fruits had higher cell density but smaller cell size compared with normal pollinated fruits. CPPU promotes the accumulation of gibberellin (GA) and auxin and decreases the level of abscisic acid (ABA) during fruit set. Moreover, application of the GA inhibitor paclobutrazol (PAC) partially inhibits CPPU-induced fruit set. Transcriptome analysis revealed that CPPU-induced fruit set specifically induced the GA-related pathway, in which the key synthase encoding gibberellin 20-oxidase 1 (CmGA20ox1) was specifically upregulated. Further study indicated that the two-component response regulator 2 (CmRR2) of the cytokinin signaling pathway, which is highly expressed at fruit setting, positively regulates the expression of CmGA20ox1. Collectively, our study determined that CPPU-induced melon fruit set is dependent on GA biosynthesis, providing a theoretical basis for the creation of parthenocarpic melon germplasm.

Spatiotemporal, physiological and transcriptomic dynamics of wild jujube seedlings under saline conditions

Soil salinity is a major constraint limiting jujube production in China. Wild jujube (Ziziphus jujuba var. spinosa (Bunge) Hu ex H. F. Chow) is widely used as the rootstock of jujube (Z. jujuba) to overcome the saline conditions. To understand the adaptive mechanism in wild jujube under saline conditions, we combined spatiotemporal and physiological assessments with transcriptomic analysis on wild jujube seedlings undergoing various salt treatments. These salt treatments showed dose and duration effects on biomass, photosynthesis, (K+) and (Na+) accumulation. Salt treatments induced higher levels of salicylic acid in roots and leaves, whereas foliar abscisic acid was also elevated after 8 days. The number of differential expression genes increased with higher doses and also longer exposure of NaCl treatments, with concomitant changes in the enriched Gene Ontology terms that were indicative of altered physiological activities. Gene co-expression network analysis identified the core gene sets associated with salt-induced changes in leaves, stems and roots, respectively. The nitrogen transporters, potassium transporters and a few transcription factors belonging to WRKY/MYB/bHLH families were clustered as the hub genes responding to salt treatments, which were related to elevated nitrogen and K+/Na+. Ectopic overexpression of two WRKY transcription factor genes (ZjWRKY6 and ZjWRKY65) conferred stronger salt-tolerance in Arabidopsis thaliana transformants by enhancing the activities of antioxidant enzymes, decreasing malondialdehyde accumulation and maintaining K+/Na+ homeostasis. This study provided evidence about the spatiotemporal, physiological and transcriptomic dynamics of wild jujube during salt stress and identified potential genes for further research to improve salt tolerance in jujube.

Carbon and nitrogen metabolism affects kentucky bluegrass rhizome expansion

BACKGROUND

Rhizome is vital for carbon and nitrogen metabolism of the whole plant. However, the effect of carbon and nitrogen in the rhizome on rhizome expansion remains unclear.

RESULTS

Three wild Kentucky bluegrass (Poa pratensis L.) germplasms with different rhizome expansion capacity (strong expansion capacity, 'YZ'; medium expansion capacity, 'WY'; and weak expansion capacity, 'AD') were planted in the field and the rhizomes number, tiller number, rhizome dry weight, physiological indicators and enzyme activity associated carbon and nitrogen metabolisms were measured. Liquid chromatography coupled to mass spectrometry (LC-MS) was utilized to analyze the metabolomic of the rhizomes. The results showed that the rhizome and tiller numbers of the YZ were 3.26 and 2.69-fold of that of the AD, respectively. The aboveground dry weight of the YZ was the greatest among all three germplasms. Contents of soluble sugar, starch, sucrose, NO₃^--N, and free amino acid were significantly higher in rhizomes of the YZ than those of the WY and AD (P < 0.05). The activities of glutamine synthetase (GS), glutamate dehydrogenase (GDH) and sucrose phosphate synthase (SPS) of the YZ were the highest among all three germplasm, with values of 17.73 A·g^- 1 h^- 1, 5.96 µmol·g^- 1 min^- 1, and 11.35 mg·g^- 1 h^- 1, respectively. Metabolomics analyses revealed that a total of 28 differentially expressed metabolites (DEMs) were up-regulated, and 25 DEMs were down-regulated in both comparison groups (AD vs. YZ group and WY vs. YZ group). Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis demonstrated that metabolites related to histidine metabolism, tyrosine metabolism, tryptophan metabolism, and phenylalanine metabolism were associated with rhizomes carbon and nitrogen metabolism.

CONCLUSIONS

Overall, the results suggest that soluble sugar, starch, sucrose, NO₃^--N, and free amino acid in rhizome are important to and promote rhizome expansion in Kentucky bluegrass, while tryptamine, 3-methylhistidine, 3-indoleacetonitrile, indole, and histamine may be key metabolites in promoting carbon and nitrogen metabolism of rhizome.

MicroRNA156ab regulates apple plant growth and drought tolerance by targeting transcription factor MsSPL13

Drought stress substantially reduces the productivity of apple plants and severely restricts the development of the apple industry. Malus sieversii, a wild apple with excellent drought resistance, is a valuable wild resource for rootstock improvement of cultivated apple (Malus domestica). miRNAs and their targets play essential roles in plant growth and stress responses, but their roles in drought stress responses in apple are unknown. Here, we demonstrate that microRNA156ab is upregulated in M. sieversii in response to drought stress. Overexpressing msi-miR156ab promoted auxin accumulation, maintained the growth of apple plants, and increased plant resistance to osmotic stress. Antioxidant enzyme activities and proline contents were also increased in miR156ab-OE transgenic apple lines, which improved drought resistance. The SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) transcription factor MsSPL13 is the target of msi-miR156ab, as demonstrated by 5-RACE and dual luciferase assays. Heterologous expression of MsSPL13 decreased auxin contents and inhibited growth in Arabidopsis (Arabidopsis thaliana) under normal and stress conditions. The activities of antioxidant enzymes were also suppressed in MsSPL13-OE transgenic Arabidopsis, reducing drought resistance. We showed that MsSPL13 regulates the expression of the auxin-related genes MsYUCCA5, PIN-FORMED7 (MsPIN7), and Gretchen Hagen3-5 (MsGH3-5) by binding to the GTAC cis-elements in their promoters, thereby regulating auxin metabolism. Finally, we demonstrated that the miR156ab-SPL13 module is involved in mediating the difference in auxin metabolism and stress responses between the M. sieversii and M26 (M. domestica) rootstocks. Overall, these findings reveal that the miR156ab-SPL13 module enhances drought stress tolerance in apples by regulating auxin metabolism and antioxidant enzyme activities.

Asymmetric cell division in plant development

Asymmetric cell division (ACD) is a fundamental process that generates new cell types during development in eukaryotic species. In plant development, post-embryonic organogenesis driven by ACD is universal and more important than in animals, in which organ pattern is preset during embryogenesis. Thus, plant development provides a powerful system to study molecular mechanisms underlying ACD. During the past decade, tremendous progress has been made in our understanding of the key components and mechanisms involved in this important process in plants. Here, we present an overview of how ACD is determined and regulated in multiple biological processes in plant development and compare their conservation and specificity among different model cell systems. We also summarize the molecular roles and mechanisms of the phytohormones in the regulation of plant ACD. Finally, we conclude with the overarching paradigms and principles that govern plant ACD and consider how new technologies can be exploited to fill the knowledge gaps and make new advances in the field.

Functional redundancy of OsPIN1 paralogous genes in regulating plant growth and development in rice

The OsPIN1 paralogous genes (OsPIN1a-1d) are important for root and panicle development in rice (Oryza sativa L.). However, the specific role of OsPIN1 paralogous genes is still not clear. To understand the specific roles of PIN1 paralogs in rice, we generated pin1 triple and quadruple mutants by crossing the pin1a pin1b and pin1c pin1d double mutants which we previously created. Compared with the 7-day-old wild type, the pin1a pin1c pin1d and pin1b pin1c pin1d triple mutants showed no obvious phenotype variation except that the pin1a pin1c pin1d triple mutant had shorter primary root and shoot. The pin1a pin1b pin1c and pin1a pin1b pin1d triple mutants exhibited a series of developmental abnormalities, including shorter primary roots, longer root hairs, fewer crown roots and lateral roots, shorter and curved shoots. Furthermore, the pin1a pin1b pin1c pin1d quadruple mutant displayed more severe phenotypic defects which was lethal. In addition, the expression levels of some hormone signal transduction and crown root development related genes, such as OsIAAs, OsARFs, OsRRs, and OsCRLs, were significantly altered in the stem base of all examined pin1 multiple mutants. Taken together, our results demonstrated that the four OsPIN1 paralogous genes function redundantly in regulating rice growth and development.

Phosphorus Recycling, Biocontrol, and Growth Promotion Capabilities of Soil Bacterial Isolates from Mexican Oak Forests: An Alternative to Reduce the Use of Agrochemicals in Maize Cultivation

Six bacteria (Bacillus velezensis 13, Bacillus subtillis 42, Pseudomonas fluorescens E221, Pseudomonas Poae EE12, Rahnella sp. EM1, and Serratia sp. EM2) isolated from the soil and litter of Mexican oak forests were characterized by identifying their ability to acquire phosphorus from different sources, analyzed for their biocontrol capabilities against two different phytopathogenic fungi, and finally tested for their ability to stimulate the germination of maize seeds and promotion of maize seedling growth. The greatest capacity to biocontrol the mycelial growth of phytopathogenic fungi Botrytis cinerea and Fusarium oxysporum was found in B. velezensis 13 and B. subtillis 42. P. poae EE12 and P. fluorescens E221 significantly promoted germination and the length of the primary root in Zea mays. Rahnella sp. EM1 and Serratia sp. EM2 could produce indole compounds related to auxin synthesis and increased the fresh weight of the maize seedlings. Together, these isolates represent an alternative to reduce the use of agrochemicals in maize cultivation. In general, soil microorganisms from Mexican oak forests represent a source of genetic resources for the sustainable management and conservation of soils for agricultural use.

Autotetraploidization Gives Rise to Differential Gene Expression in Response to Saline Stress in Rice

Plant polyploidization represents an effective means for plants to perpetuate their adaptive advantage in the face of environmental variation. Numerous studies have identified differential responsiveness to environmental cues between polyploids and their related diploids, and polyploids might better adapt to changing environments. However, the mechanism that underlies polyploidization contribution during abiotic stress remains hitherto obscure and needs more comprehensive assessment. In this study, we profile morphological and physiological characteristics, and genome-wide gene expression between an autotetraploid rice and its diploid donor plant following saline stress. The results show that the autotetraploid rice is more tolerant to saline stress than its diploid precursor. The physiological characteristics were rapidly responsive to saline stress in the first 24 h, during which the elevations in sodium ion, superoxide dismutase, peroxidase, and 1-aminocyclopropane-1-carboxylic acid were all significantly higher in the autotetraploid than in the diploid rice. Meanwhile, the genome-wide gene expression analysis revealed that the genes related to ionic transport, peroxidase activity, and phytohormone metabolism were differentially expressed in a significant manner between the autotetraploid and the diploid rice in response to saline stress. These findings support the hypothesis that diverse mechanisms exist between the autotetraploid rice and its diploid donor plant in response to saline stress, providing vital information for improving our understanding on the enhanced performance of polyploid plants in response to salt stress.

The roles of epigenetic modifications in the regulation of auxin biosynthesis

Auxin is one of the most important plant growth regulators of plant morphogenesis and response to environmental stimuli. Although the biosynthesis pathway of auxin has been elucidated, the mechanisms regulating auxin biosynthesis remain poorly understood. The transcription of auxin biosynthetic genes is precisely regulated by complex signaling pathways. When the genes are expressed, epigenetic modifications guide mRNA synthesis and therefore determine protein production. Recent studies have shown that different epigenetic factors affect the transcription of auxin biosynthetic genes. In this review, we focus our attention on the molecular mechanisms through which epigenetic modifications regulate auxin biosynthesis.

Acidic and Alkaline Conditions Affect the Growth of Tree Peony Plants via Altering Photosynthetic Characteristics, Limiting Nutrient Assimilation, and Impairing ROS Balance

Exposure to acidic and alkaline conditions were found to cause the excess accumulation of reactive oxygen species in tree peony, thereby causing damage and inhibiting plant growth and development. The activities of antioxidant enzymes were also found to be significantly up-regulated, especially under alkaline conditions; this explained why tree peony is better adapted to alkaline than to acidic conditions. Through pairwise comparisons, 144 differentially expressed genes (DEGs) associated with plant growth, photosynthesis, and stress were identified. The DEGs related to stress were up-regulated, whereas the remaining DEGs were almost all down-regulated after acid and alkaline treatments. The nutrient assimilation was greatly inhibited. Chlorophyll synthesis genes were suppressed, and chlorophyll content was reduced. The development and structures of stomata and chloroplasts and the transcription of related genes were also influenced. Among photosynthesis-related DEGs, electron transport chains were the most sensitive. The suppressed expression of photosynthesis genes and the reduced light-harvesting capacity, together with the impairment of chloroplasts and stomata, finally led to a sharp decrease in the net photosynthetic rate. Carbohydrate accumulation and plant biomass were also reduced. The present study provides a theoretical basis for the response mechanisms of tree peony to adverse pH conditions and enriches knowledge of plant adaptation to alkaline conditions.

Isolation of indole-3-acetic acid-producing Azospirillum brasilense from Vietnamese wet rice: co-immobilization of isolate and microalgae as a sustainable biorefinery

Production of indole-3-acetic acid (IAA) is well documented in various studies for the bacteria that inhabit the rhizosphere of plants, but with roots of wet rice, the outstandings have been not yet elucidated. This study began with the isolation of bacteria type strain Azospirillum sp. and developed the investigation to a screening of their ability in IAA production. This screening conducted a selection of only bacteria that was capable of the production of IAA with its content of over 25µg. mL^-1 for sequencing. Of 10 isolates only one resulted from the type strain Azospirillum brasilense (A. brasilense) with a similarity of 100%. Various factors that influence A. brasilense in biosynthesizing IAA such as temperature, pH, nitrogen presence and concentration of tryptophan in the culture medium were examined. The results indicated that the culture conditions were suitable for IAA biosynthesis at pH 6.5, 30°C, culture media with nitrogen, and 0.1% trytophan. The next survey on the role of the immobilization of this bacteria with microalgae in alginate was highlighted to its support in microalgal growth. With the co-immobilization of bacteria and microalgae, the density of Chlorella vulgaris was significantly increased during 15-day culture, inducing 2.2 times of cell content in culture batch microalgae immobilized A. brasilense higher than that free-bacteria.

Spatiotemporal auxin distribution in Arabidopsis tissues is regulated by anabolic and catabolic reactions under long-term ammonium stress

BACKGROUND

The plant hormone auxin is a major coordinator of plant growth and development in response to diverse environmental signals, including nutritional conditions. Sole ammonium (NH₄⁺) nutrition is one of the unique growth-suppressing conditions for plants. Therefore, the quest to understand NH₄⁺-mediated developmental defects led us to analyze auxin metabolism.

RESULTS

Indole-3-acetic acid (IAA), the most predominant natural auxin, accumulates in the leaves and roots of mature Arabidopsis thaliana plants grown on NH₄⁺, but not in the root tips. We found changes at the expressional level in reactions leading to IAA biosynthesis and deactivation in different tissues. Finally, NH₄⁺ nutrition would facilitate the formation of inactive oxidized IAA as the final product.

CONCLUSIONS

NH₄⁺-mediated accelerated auxin turnover rates implicate transient and local IAA peaks. A noticeable auxin pattern in tissues correlates with the developmental adaptations of the short and highly branched root system of NH₄⁺-grown plants. Therefore, the spatiotemporal distribution of auxin might be a root-shaping signal specific to adjust to NH₄⁺-stress conditions.

Identification, analysis, and modeling of the YUCCA protein family genome-wide in Coffea canephora

Auxin is involved in almost every aspect of plant growth and development, from embryogenesis to senescence. Indole-3-acetic acid (IAA) is the main known natural auxin that is synthesized by enzymes tryptophan aminotransferase of arabidopsis (TAA) and YUCCA (YUC) of the flavin-containing monooxygenases family (FMO) from one of the tryptophan-dependent pathways. Genome-wide identification and comprehensive analysis of the YUC-protein family have been conducted in Coffea canephora in the present study. A total of 10 members CcYUC gene family were identified in C. canephora. Phylogenetic analysis revealed that the CcYUC protein family is evolutionarily conserved, and they consist of four groups. In contrast, bioinformatic analysis predicted a hydrophobic transmembrane helix (TMH) for one CcYUC (YUC10) member only. Isoelectric point (pI), molecular mass (Ms), signal peptide, subcellular localization, and phosphorylation sites were predicted for CcYUC proteins. YUC enzymes require the prosthetic group flavin adenine dinucleotide (FAD) and the cofactor nicotinamide adenine dinucleotide phosphate (NADPH) for their enzymatic activity. Therefore, we include the molecular docking for CcYUC2-FAD-NADPH-IPyA and yucasin, which is a specific inhibitor for YUC activity. The docking results showed FAD and NADPH binding at the big and small domain sites, respectively, in CcYUC2. IPyA binds very close to FAD along the big domain, and yucasin competes for the same site as IPA, blocking IAA production. Furthermore, in silico point mutations affect the stability of the CcYUC2-4 proteins.

Hydrogen Sulfide Improves the Cold Stress Resistance through the CsARF5-CsDREB3 Module in Cucumber

As an important gas signaling molecule, hydrogen sulfide (H₂S) plays a crucial role in regulating cold tolerance. H₂S cooperates with phytohormones such as abscisic acid, ethylene, and salicylic acid to regulate the plant stress response. However, the synergistic regulation of H₂S and auxin in the plant response to cold stress has not been reported. This study showed that sodium hydrosulfide (NaHS, an H₂S donor) treatment enhanced the cold stress tolerance of cucumber seedlings and increased the level of auxin. CsARF5, a cucumber auxin response factor (ARF) gene, was isolated, and its role in regulating H₂S-mediated cold stress tolerance was described. Transgenic cucumber leaves overexpressing CsARF5 were obtained. Physiological analysis indicated that overexpression of CsARF5 enhanced the cold stress tolerance of cucumber and the regulation of the cold stress response by CsARF5 depends on H₂S. In addition, molecular assays showed that CsARF5 modulated cold stress response by directly activating the expression of the dehydration-responsive element-binding (DREB)/C-repeat binding factor (CBF) gene CsDREB3, which was identified as a positive regulator of cold stress. Taken together, the above results suggest that CsARF5 plays an important role in H₂S-mediated cold stress in cucumber. These results shed light on the molecular mechanism by which H₂S regulates cold stress response by mediating auxin signaling; this will provide insights for further studies on the molecular mechanism by which H₂S regulates cold stress. The aim of this study was to explore the molecular mechanism of H₂S regulating cold tolerance of cucumber seedlings and provide a theoretical basis for the further study of cucumber cultivation and environmental adaptability technology in winter.

H2O2 Functions as a Downstream Signal of IAA to Mediate H2S-Induced Chilling Tolerance in Cucumber

Hydrogen sulfide (H₂S) plays a crucial role in regulating chilling tolerance. However, the role of hydrogen peroxide (H₂O₂) and auxin in H₂S-induced signal transduction in the chilling stress response of plants was unclear. In this study, 1.0 mM exogenous H₂O₂ and 75 μM indole-3-acetic acid (IAA) significantly improved the chilling tolerance of cucumber seedlings, as demonstrated by the mild plant chilling injury symptoms, lower chilling injury index (CI), electrolyte leakage (EL), and malondialdehyde content (MDA) as well as higher levels of photosynthesis and cold-responsive genes under chilling stress. IAA-induced chilling tolerance was weakened by N, N′-dimethylthiourea (DMTU, a scavenger of H₂O₂), but the polar transport inhibitor of IAA (1-naphthylphthalamic acid, NPA) did not affect H₂O₂-induced mitigation of chilling stress. IAA significantly enhanced endogenous H₂O₂ synthesis, but H₂O₂ had minimal effects on endogenous IAA content in cucumber seedlings. In addition, the H₂O₂ scavenger DMTU, inhibitor of H₂O₂ synthesis (diphenyleneiodonium chloride, DPI), and IAA polar transport inhibitor NPA reduced H₂S-induced chilling tolerance. Sodium hydrosulfide (NaHS) increased H₂O₂ and IAA levels, flavin monooxygenase (FMO) activity, and respiratory burst oxidase homolog (RBOH1) and FMO-like protein (YUCCA2) mRNA levels in cucumber seedlings. DMTU, DPI, and NPA diminished NaHS-induced H₂O₂ production, but DMTU and DPI did not affect IAA levels induced by NaHS during chilling stress. Taken together, the present data indicate that H₂O₂ as a downstream signal of IAA mediates H₂S-induced chilling tolerance in cucumber seedlings.

NB-LRR genes: characteristics in three Solanum species and transcriptional response to Ralstonia solanacearum in tomato

NB-LRR genes in the three Solanum species showed specific constitution characteristics and evolved multiple clusters and duplicates. Some genes could respond to biotic stresses such as tomato bacterial wilt. Nucleotide-binding and leucine-rich repeat (NB-LRR, NLR) is a largest resistance gene family in plants, which plays a key role in response to biotic stresses. In this study, NB-LRR genes in cultivated tomato Solanum lycopersicum (Sl) and its wild relatives S. pennellii (Spe) and S. pimpinellifolium (Spi) were analyzed using bioinformatics approaches. In total, 238, 202 and 217 NB-LRR genes of 8 different types were found in Sl, Spe and Spi, respectively. The three species showed similar genomic characteristics. The NB-LRR genes were mainly distributed on chromosomes 4, 5 and 11 and located at the distal zones, forming multiple clusters and tandem duplicates. A large number of homologs appeared through gene expansion, with most Ka/Ks values being less than 1, indicating that purifying selection had occurred in evolution. These genes were mainly expressed in root and could respond to different biotic stresses. RT-qPCR analysis revealed that SlNLR genes could respond to tomato bacterial wilt, with SlNLR1 probably involved in the resistance response, whereas others being the opposite. The transcription factors (TFs) and interaction proteins that regulate target genes were mainly Dof, NAC and MYB families and kinases. The results provide a basis for the isolation and application of related genes in plant disease resistance breeding.

Cytokinin-Controlled Gradient Distribution of Auxin in Arabidopsis Root Tip

The plant root is a dynamic system, which is able to respond promptly to external environmental stimuli by constantly adjusting its growth and development. A key component regulating this growth and development is the finely tuned cross-talk between the auxin and cytokinin phytohormones. The gradient distribution of auxin is not only important for the growth and development of roots, but also for root growth in various response. Recent studies have shed light on the molecular mechanisms of cytokinin-mediated regulation of local auxin biosynthesis/metabolism and redistribution in establishing active auxin gradients, resulting in cell division and differentiation in primary root tips. In this review, we focus our attention on the molecular mechanisms underlying the cytokinin-controlled auxin gradient in root tips.

Recent Advances in Understanding Mechanisms of Plant Tolerance and Response to Aluminum Toxicity

Aluminum (Al) toxicity is a major environmental stress that inhibits plant growth and development. There has been impressive progress in recent years that has greatly increased our understanding of the nature of Al toxicity and its mechanisms of tolerance. This review describes the transcription factors (TFs) and plant hormones involved in the adaptation to Al stress. In particular, it discusses strategies to confer plant resistance to Al stress, such as transgenic breeding, as well as small molecules and plant growth-promoting rhizobacteria (PGPRs) to alleviate Al toxicity. This paper provides a theoretical basis for the enhancement of plant production in acidic soils.

Plant cell totipotency: Insights into cellular reprogramming

Plant cells have a powerful capacity in their propagation to adapt to environmental change, given that a single plant cell can give rise to a whole plant via somatic embryogenesis without the need for fertilization. The reprogramming of somatic cells into totipotent cells is a critical step in somatic embryogenesis. This process can be induced by stimuli such as plant hormones, transcriptional regulators and stress. Here, we review current knowledge on how the identity of totipotent cells is determined and the stimuli required for reprogramming of somatic cells into totipotent cells. We highlight key molecular regulators and associated networks that control cell fate transition from somatic to totipotent cells. Finally, we pose several outstanding questions that should be addressed to enhance our understanding of the mechanisms underlying plant cell totipotency.

Roles of YABBY transcription factors in the modulation of morphogenesis, development, and phytohormone and stress responses in plants

The YABBY family is a class of plant-specific transcription factors comprising a typical N-terminal C2C2-type zinc finger domain and a C-terminal helix-loop-helix YABBY domain. YABBY transcription factors play important roles in multiple biological processes, including polarity establishment in plant leaves, the formation and development of reproductive organs, the response to plant hormone signals, resistance to stress, crop breeding and agricultural production. The aim of this review is to summarize our current understanding of the roles, functions and value of the YABBY family in plants, with particular emphasis on new insights into the molecular and physiological mechanisms involved in the YABBY-mediated modulation of polarity establishment, morphogenesis and development, and phytohormone and stress responses in plants. In addition, we propose that this transcription factor family presents great value and potential for research, application and development in crop breeding and agricultural production in the future.

How Plant Hormones Mediate Salt Stress Responses

Salt stress is one of the major environmental stresses limiting plant growth and productivity. To adapt to salt stress, plants have developed various strategies to integrate exogenous salinity stress signals with endogenous developmental cues to optimize the balance of growth and stress responses. Accumulating evidence indicates that phytohormones, besides controlling plant growth and development under normal conditions, also mediate various environmental stresses, including salt stress, and thus regulate plant growth adaptation. In this review, we mainly discuss and summarize how plant hormones mediate salinity signals to regulate plant growth adaptation. We also highlight how, in response to salt stress, plants build a defense system by orchestrating the synthesis, signaling, and metabolism of various hormones via multiple crosstalks.

Improved reproductive growth of euhalophyte Suaeda salsa under salinity is correlated with altered phytohormone biosynthesis and signal transduction

Phytohormones are essential for plant reproductive growth. Salinity limits crop reproductive growth and yield, but improves reproductive growth of euhalophytes. However, little is known about the mechanisms underlying salinity's effects on plant reproductive growth. To elucidate the role of plant hormones in flower development of the euhalophyte Suaeda salsa under saline conditions, we analysed endogenous gibberellic acid (GA3,4), indoleacetic acid (IAA), zeatin riboside (ZR), abscisic acid (ABA), and brassinosteroids (BRs) during flowering in control (0 mM) and NaCl-treated (200 mM) plants. At the end of vegetative growth, endogenous GA3, GA4, ABA and BR contents in stems of NaCl-treated plants were significantly higher than those in controls. During flowering, GA3, GA4, IAA and ZR contents showed the most significant enhancement in flower organs of plants treated with NaCl when compared with controls. Additionally, genes related to ZR, IAA, GA, BR and ABA biosynthesis and plant hormone signal transduction, such as those encoding CYP735A, CYP85A, GID1, NCED, PIF4, AHP, TCH4, SnRK2 and ABF, were upregulated in S. salsa flowers from NaCl-treated plants. These results suggest that coordinated upregulation of genes involved in phytohormone biosynthesis and signal transduction contributes to the enhanced reproductive growth of S. salsa under salinity.

Mechanisms of Waterlogging Tolerance in Plants: Research Progress and Prospects

Waterlogging is one of the main abiotic stresses suffered by plants. Inhibition of aerobic respiration during waterlogging limits energy metabolism and restricts growth and a wide range of developmental processes, from seed germination to vegetative growth and further reproductive growth. Plants respond to waterlogging stress by regulating their morphological structure, energy metabolism, endogenous hormone biosynthesis, and signaling processes. In this updated review, we systematically summarize the changes in morphological structure, photosynthesis, respiration, reactive oxygen species damage, plant hormone synthesis, and signaling cascades after plants were subjected to waterlogging stress. Finally, we propose future challenges and research directions in this field.

Epigenetic Regulation of Auxin Homeostasis

Epigenetic regulation involves a myriad of mechanisms that regulate the expression of loci without altering the DNA sequence. These different mechanisms primarily result in modifications of the chromatin topology or DNA chemical structure that can be heritable or transient as a dynamic response to environmental cues. The phytohormone auxin plays an important role in almost every aspect of plant life via gradient formation. Auxin maxima/minima result from a complex balance of metabolism, transport, and signaling. Although epigenetic regulation of gene expression during development has been known for decades, the specific mechanisms behind the spatiotemporal dynamics of auxin levels in plants are only just being elucidated. In this review, we gather current knowledge on the epigenetic mechanisms regulating the expression of genes for indole-3-acetic acid (IAA) metabolism and transport in Arabidopsis and discuss future perspectives of this emerging field.

Molecular Responses during Plant Grafting and Its Regulation by Auxins, Cytokinins, and Gibberellins

Plant grafting is an important horticulture technique used to produce a new plant after joining rootstock and scion. This is one of the most used techniques by horticulturists to enhance the quality and production of various crops. Grafting helps in improving the health of plants, their yield, and the quality of plant products, along with the enhancement of their postharvest life. The main process responsible for successful production of grafted plants is the connection of vascular tissues. This step determines the success rate of grafts and hence needs to be studied in detail. There are many factors that regulate the connection of scion and stock, and plant hormones are of special interest for researchers in the recent times. These phytohormones act as signaling molecules and have the capability of translocation across the graft union. Plant hormones, mainly auxins, cytokinins, and gibberellins, play a major role in the regulation of various key physiological processes occurring at the grafting site. In the current review, we discuss the molecular mechanisms of graft development and the phytohormone-mediated regulation of the growth and development of graft union.

The Nuts and Bolts of PIN Auxin Efflux Carriers

The plant-specific proteins named PIN-FORMED (PIN) efflux carriers facilitate the direction of auxin flow and thus play a vital role in the establishment of local auxin maxima within plant tissues that subsequently guide plant ontogenesis. They are membrane integral proteins with two hydrophobic regions consisting of alpha-helices linked with a hydrophilic loop, which is usually longer for the plasma membrane-localized PINs. The hydrophilic loop harbors molecular cues important for the subcellular localization and thus auxin efflux function of those transporters. The three-dimensional structure of PIN has not been solved yet. However, there are scattered but substantial data concerning the functional characterization of amino acid strings that constitute these carriers. These sequences include motifs vital for vesicular trafficking, residues regulating membrane diffusion, cellular polar localization, and activity of PINs. Here, we summarize those bits of information striving to provide a reference to structural motifs that have been investigated experimentally hoping to stimulate the efforts toward unraveling of PIN structure-function connections.