Graphene oxide and ABA cotreatment regulates root growth of Brassica napus L. by regulating IAA/ABA

The transcription factor TaFDL2-1A functions in auxin metabolism mediated by abscisic acid to regulate shoot growth in wheat

Genetic strategies can be effective in improving wheat (Triticum aestivum L.) drought stress tolerance, but accumulating evidence suggests that overexpressing drought-resistance genes, especially genes related to the abscisic acid (ABA) signaling pathway, can retard plant growth. We previously characterized the positive roles of the wheat bZIP transcription factor TaFD-Like2-1A (TaFDL2-1A) in drought stress tolerance and ABA biosynthesis and response, whereas a dwarfing shoot exhibited under normal conditions. This study determined the underlying mechanisms that allow TaFDL2-1A to affect shoot growth. Overexpressing TaFDL2-1A decreased cell length, cell width, leaf size, shoot length, and biomass in wheat. The results of RNA-seq showed that multiple differently expressed transcripts are enriched in the auxin signaling pathway. Further analysis indicated higher expression levels of Gretchen Hagen3 (GH3) genes and lower indole-3-acetic acid (IAA) concentrations in the TaFDL2-1A overexpression lines. Exogenous IAA treatment restored the phenotypes of the TaFDL2-1A overexpression lines to wild-type levels. Transcriptional regulation analysis suggested that TaFDL2-1A enhances the expression of auxin metabolism genes, such as TaGH3.2-3A, TaGH3.2-3B, TaGH3.8-2A, and TaGH3.8-2D, by directly binding to ACGT core cis-elements. Furthermore, tafdl2 knockout plants had lower expression levels of these GH3 genes and higher IAA levels than Fielder wheat. These GH3 gene expression and IAA levels were induced and reduced in Fielder wheat and tafdl2 knockout plants treated with exogenous ABA. Our findings elucidate mechanisms underlying the functional redundancy of TaFDL2-1A in the crosstalk between ABA and IAA to affect shoot growth and provide insights into the balance between drought resistance and yield in wheat.

CBP60b clade proteins are prototypical transcription factors mediating immunity

Transcriptional reprogramming is critical for plant immunity. Several calmodulin (CaM)-binding protein 60 (CBP60) family transcription factors (TFs) in Arabidopsis (Arabidopsis thaliana), including CBP60g, systemic acquired resistance deficient 1 (SARD1), CBP60a, and CBP60b, are critical for and show distinct roles in immunity. However, there are additional CBP60 members whose function is unclear. We report here that Arabidopsis CBP60c-f, 4 uncharacterized CBP60 members, play redundant roles with CBP60b in the transcriptional regulation of immunity responses, whose pCBP60b-driven expression compensates the loss of CBP60b. By contrast, neither CBP60g nor SARD1 is interchangeable with CBP60b, suggesting clade-specific functionalization. We further show that the function of CBP60b clade TFs relies on DNA-binding domains (DBDs) and CaM-binding domains, suggesting that they are downstream components of calcium signaling. Importantly, we demonstrate that CBP60s encoded in earliest land plant lineage Physcomitrium patens and Selaginella moellendorffii are functionally homologous to Arabidopsis CBP60b, suggesting that the CBP60b clade contains the prototype TFs of the CBP60 family. Furthermore, tomato and cucumber CBP60b-like genes rescue the defects of Arabidopsis cbp60b and activate the expression of tomato and cucumber SALICYLIC ACID INDUCTION DEFICIIENT2 (SID2) and ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1) genes, suggesting that immune response pathways centered on CBP60b are also evolutionarily conserved. Together, these findings suggest that CBP60b clade TFs are functionally conserved in evolution and positively mediate immunity.

Interspecific grafting promotes poplar growth and drought resistance via regulating phytohormone signaling and secondary metabolic pathways

Populus cathayana (C) grafted onto P. deltoides (D) (C/D) can promote growth better than self-grafting (C/C and D/D). However, the mechanisms underlying growth and resistance to drought stress are not clear. In this study, we performed physiological and RNA-seq analysis on the different grafted combinations. It was found that C/D plants exhibited higher growth, net photosynthetic rate, IAA content and intrinsic water use efficiency (WUEi) than C/C and D/D plants under both well-watered and drought-stressed conditions. However, most growth, photosynthetic indices, and IAA content were decreased less in C/D, whereas ABA content, WUEi and root characteristics (e.g., root length, volume, surface area and vitality) were increased more in C/D than in other grafting combinations under drought-stressed conditions. Transcriptomic analysis revealed that the number of differentially expressed genes (DEGs) in leaves of C/D vs C/C (control, 181; drought, 121) was much lower than that in the roots of C/D vs D/D (control, 1639; drought, 1706), indicating that the rootstocks were more responsive to drought resistance. KEGG and GO functional enrichment analysis showed that the enhanced growth and drought resistance of C/D were mainly related to DEGs involved in the pathways of ABA and IAA signaling, and secondary metabolite biosynthesis, especially the pathways for lignin and dopamine synthesis and metabolism. Therefore, our results further demonstrated the dominant role of rootstock in drought resistance, and enriched our knowledge on the mechanism of how interspecific grafting enhanced the growth and drought resistance in poplar.

Overexpression of BnMYBL2-1 improves plant drought tolerance via the ABA-dependent pathway

Drought stress is a major environmental challenge that poses considerable threats to crop survival and growth. Previous research has indicated anthocyanins play a crucial role in alleviating oxidative damage, photoprotection, membrane stabilization, and water retention under drought stress. However, the presence of MYBL2 (MYELOBBLASTOSIS LIKE 2), an R3-MYB transcription factor (TF) which known to suppress anthocyanin biosynthesis. In this study, four BnMYBL2 members were cloned from Brassica napus L, and BnMYBL2-1 was overexpressed in Triticum aestivum L (No BnMYBL2 homologous gene was detected in wheat). Subsequently, the transgenic wheat lines were treated with drought, ABA and anthocyanin. Results showed that transgenic lines exhibited greater drought tolerance compared to the wild-type (WT), characterized by improved leaf water content (LWC), elevated levels of soluble sugars and chlorophyll, and increased antioxidant enzyme activity. Notably, transgenic lines also exhibited significant upregulation in abscisic acid (ABA) content, along with the transcriptional levels of key enzymes involved in ABA signalling under drought. Results also demonstrated that BnMYBL2-1 promoted the accumulation of ABA and anthocyanins in wheat. Overall, the study highlights the positive role of BnMYBL2-1 in enhancing crop drought tolerance through ABA signalling and establishes its close association with anthocyanin biosynthesis. These findings offer valuable insights for the development of drought-resistant crop varieties and enhance the understanding of the molecular mechanisms underlying plant responses to drought stress.

Untargeted metabolism approach reveals difference of varieties of bud and relation among characteristics of grafting seedlings in Camellia oleifera

Camellia oleifera is one of the essential wood oil trees in the world. C.oleifera was propagated by nurse seedling grafting. Since the scion of C.oleifera had a significant regulated effect on the properties of rootstock after grafting and impacted on the growth of the grafted seedlings, it was necessary to understand the characteristics of buds among varieties to cultivate high-quality grafted seedlings. The metabolome was thought to be a powerful tool for understanding connecting phenotype-genotype interactions, which has an important impact on plant growth and development. In this study, UPLC-MS was used to determine the metabolites of the apical buds of CL3, CL4, CL40, and CL53 spring shoots after 30 days of sprout and to measure the growth characteristics of roots and stems after grafting. Metabolomics analysis revealed 554 kinds of metabolites were significant differences among four varieties, and 29 metabolic pathways were identified to have significant changes (p< 0.05), including carboxylic acids and derivatives, fatty Acyls, organooxygen compounds, and prenol lipids metabolites. The metabolites appeared in all varieties, including phenethyl rutinoside in glycosyl compounds and hovenidulcioside A1 in terpene glycosides. Metabolite-metabolite correlations in varieties revealed more complex patterns in relation to bud and enabled the recognition of key metabolites (e.g., Glutamate, (±)Catechin, GA₅₂, ABA, and cs-Zeatin) affecting grafting and growth ability. Each variety has a unique metabolite type and correlation network relationship. Differentiated metabolites showed different growth trends for development after grafting. Many metabolites regulate the growth of scions in buds before grafting, which plays a crucial role in the growth of seedlings after grafting. It not only regulates the growth of roots but also affects the development of this stem. Finally, those results were associated with the genetic background of each cultivar, showing that metabolites could be potentially used as indicators for the genetic background, indicating that metabolites could potentially be used as indicators for seedling growth characteristics. Together, this study will enrich the theoretical basis of seedling growth and lay a foundation for further research on the molecular regulation mechanism interaction between rootstock and scion, rootstock growth, and the development of grafted seedlings after grafting.

Abscisic Acid Induces Adventitious Rooting in Cucumber (Cucumis sativus L.) by Enhancing Sugar Synthesis

Abscisic acid (ABA) affects many important plant processes, such as seed germination, root elongation and stomatal movement. However, little information is available about the relationship between ABA and sugar synthesis during adventitious root formation. The aim of this study was to evaluate the effect of ABA on adventitious root formation in cucumber and whether the effect of this plant hormone on sugar synthesis could be included as a causative factor for adventitious root development. We determined the contents of glucose, sucrose, starch, total sugar and sugar-related enzymes, including sucrose synthase (SS), sucrose phosphate synthase (SPS), hexokinase (HK) and pyruvate kinase (PK) activities in ABA treatment. We also quantified the relative expression of sucrose or glucose synthesis genes during this process. Increasing ABA concentrations significantly improved adventitious root formation, with the most considerable effect at 0.05 μM. Compared to the control, ABA treatment showed higher glucose, sucrose, starch and total sugar contents. Moreover, ABA treatment increased glucose-6-phosphate (G6P), fructose-6-phosphate (F6P) and glucose-1-phosphate (G1P) contents in cucumber explants during adventitious root development, which was followed by an increase of activities of sucrose-related enzymes SS and SPS, glucose-related enzymes HK and PK. ABA, meanwhile, upregulated the expression levels of sucrose or glucose synthesis-related genes, including CsSuSy1, CsSuSy6, CsHK1 and CsHK3. These results suggest that ABA may promote adventitious root development by increasing the contents of glucose, sucrose, starch, total sugar, G6P, F6P and G1P, the activities of SS, SPS, HK, SPS and the expression levels of CsSuSy1, CsSuSy6, CsHK1 and CsHK3 genes. These findings provide evidence for the physiological role of ABA during adventitious root formation and provide a new understanding of the possible relationship between ABA and sugar synthesis during adventitious rooting in plants.

The Effects of Graphene-Family Nanomaterials on Plant Growth: A Review

Numerous reports of graphene-family nanomaterials (GFNs) promoting plant growth have opened up a wide range of promising potential applications in agroforestry. However, several toxicity studies have raised growing concerns about the biosafety of GFNs. Although these studies have provided clues about the role of GFNs from different perspectives (such as plant physiology, biochemistry, cytology, and molecular biology), the mechanisms by which GFNs affect plant growth remain poorly understood. In particular, a systematic collection of data regarding differentially expressed genes in response to GFN treatment has not been conducted. We summarize here the fate and biological effects of GFNs in plants. We propose that soil environments may be conducive to the positive effects of GFNs but may be detrimental to the absorption of GFNs. Alterations in plant physiology, biochemistry, cytological structure, and gene expression in response to GFN treatment are discussed. Coincidentally, many changes from the morphological to biochemical scales, which are caused by GFNs treatment, such as affecting root growth, disrupting cell membrane structure, and altering antioxidant systems and hormone concentrations, can all be mapped to gene expression level. This review provides a comprehensive understanding of the effects of GFNs on plant growth to promote their safe and efficient use.

Integrating transcriptome and physiological analyses to elucidate the molecular responses of buckwheat to graphene oxide

With the increasing application of nanomaterials, evaluation of the phytotoxicity of nanoparticles has attracted considerable interest. Buckwheat is an economically pseudocereal crop, which is a potential model for investigating the response of plants to hazardous materials. In this study, the response of buckwheat to graphene oxide (GO) was investigated by integrating physiological and transcriptome analysis. GO can penetrate into buckwheat root and stem, and high concentrations of GO inhibited seedlings growth. High concentration of GO improved ROS production and regulated the activities and gene expression of oxidative enzymes, which implying GO may affect plant growth via regulating ROS detoxification. Root and stem exhibit distinct transcriptomic responses to GO, and the GO-responsive genes in stem are more enriched in cell cycle and epigenetic regulation. GO inhibited plant hormone biosynthesis and signaling by analyzing the expression data. Additionally, 97 small secreted peptides (SSPs) encoding genes were found to be involved in GO response. The gene expression of 111 transcription factor (TFs) and 43 receptor-like protein kinases (RLKs) were regulated by GO, and their expression showed high correlation with SSPs. Finally, the TFs-SSPs-RLKs signaling networks in regulating GO response were proposed. This study provides insights into the molecular responses of plants to GO.

Bismuth Vanadium Oxide Can Promote Growth and Activity in Arabidopsis thaliana

The excellent properties of nanomaterials have been confirmed in many fields, but their effects on plants are still unclear. In this study, different concentrations of bismuth vanadate (BV) were added to the growth medium to analyze the growth of seedlings, including taproots, lateral roots, leaf stomata, root activity, and superoxide anion O₂^.- generation. Gene expression levels related to root growth were determined by quantitative PCR in Arabidopsis thaliana. The results showed that BV promoted the growth of taproots and the development of lateral roots, enhanced the length of the extension zone in roots, increased the number and size of leaf stomata and root activity, reduced the accumulation of ROS in seedlings, and changed the expression levels of genes related to polyamines or hormones. At the same time, we investigated the antibacterial activity of BV against a variety of common pathogens causing crop diseases. The results showed that BV could effectively inhibit the growth of Fusarium wilt of cotton and rice sheath blight. These results provide a new prospect for the development of nanomaterial-assisted plants, which is expected to become one of the ways to solve the problem of controlling and promoting the development of plants. At the same time, it also provides a reference for the study of the effect of BV on plants.

A new function of white-rot fungi Ceriporia lacerata HG2011: improvement of biological nitrogen fixation of broad bean (Vicia faba)

The inoculation of plant growth-promoting microbes with multifarious functions is a simple, economic, and effective way to improve nodulation and biological nitrogen fixation (BNF) of legumes. Broad bean (Vicia faba) is commonly grown in the winter in tropics and subtropics for increasing soil N and farmers' income. The new functions of Ceriporia lacerata HG2011, a white-rot fungus, in nodulation and BNF (measured by ¹⁵N natural abundance) were studied with the broad bean in liquid culture, soil incubation, and greenhouse pot experiments. The results showed that this fungus released IAA, GA, and Fe-binding ligands into culture solutions, increased lateral roots and root surfaces, and mobilized phosphorus and iron into bioavailable forms in the soil. These performances may be beneficial to nodulation and BNF. The indigenous rhizobia that infect broad been were long-lived in the experimental soil. The efficiency of exogenous rhizobium inoculation may be unsatisfactory in the soils for frequently growing broad beans because of fierce competition with native rhizobia. Compared with no inoculation, the fungal inoculant increased nutrient (nitrogen, phosphorus, and potassium) availability in the fertilized soil, nodule mass, and plant BNF and nutrient uptake, leading to higher plant biomass and grain yield. Thus, C. lacerata HG2011 provided more potential sites for rhizobia infection in nodulation, increased nodule size, and improved nodule mineral nutrient (particularly phosphorus and iron) and photosynthate acquisitions, resulting in better nodulation and increased plant BNF. These significant findings firstly proved a new function of C. lacerata HG2011 in improving the inoculation and BNF of legume plants.

Arabidopsis LSH8 Positively Regulates ABA Signaling by Changing the Expression Pattern of ABA-Responsive Proteins

Phytohormone ABA regulates the expression of numerous genes to significantly affect seed dormancy, seed germination and early seedling responses to biotic and abiotic stresses. However, the function of many ABA-responsive genes remains largely unknown. In order to improve the ABA-related signaling network, we conducted a large-scale ABA phenotype screening. LSH, an important transcription factor family, extensively participates in seedling development and floral organogenesis in plants, but whether its family genes are involved in the ABA signaling pathway has not been reported. Here we describe a new function of the transcription factor LSH8 in an ABA signaling pathway. In this study, we found that LSH8 was localized in the nucleus, and the expression level of LSH8 was significantly induced by exogenous ABA at the transcription level and protein level. Meanwhile, seed germination and root length measurements revealed that lsh8 mutant lines were ABA insensitive, whereas LSH8 overexpression lines showed an ABA-hypersensitive phenotype. With further TMT labeling quantitative proteomic analysis, we found that under ABA treatment, ABA-responsive proteins (ARPs) in the lsh8 mutant presented different changing patterns with those in wild-type Col4. Additionally, the number of ARPs contained in the lsh8 mutant was 397, six times the number in wild-type Col4. In addition, qPCR analysis found that under ABA treatment, LSH8 positively mediated the expression of downstream ABA-related genes of ABI3, ABI5, RD29B and RAB18. These results indicate that in Arabidopsis, LSH8 is a novel ABA regulator that could specifically change the expression pattern of APRs to positively mediate ABA responses.

Graphene oxide exposure suppresses nitrate uptake by roots of wheat seedlings

Despite the large number of studies reporting the phytotoxicity of graphene-based materials, the effects of these materials on nutrient uptake in plants remain unclear. The present study showed that nitrate concentrations were significantly decreased in the roots of wheat plants treated with graphene oxide (GO) at 200-800 mg L^-1. Non-invasive microelectrode measurement demonstrated that GO could significantly inhibit the net NO₃^- influx in the meristematic, elongation, and mature zones of wheat roots. Further analysis indicated that GO could be trapped in the root vacuoles, and that the maximal root length and the number of lateral roots were significantly reduced. Additionally, root tip whitening, creases, oxidative stress, and weakened respiration were observed. These observations indicate that GO is highly unfavorable for vigorous root growth and inhibits increase in root uptake area. At the molecular level, GO exposure caused DNA damage and inhibited the expression of most nitrate transporters (NRTs) in wheat roots, with the most significantly downregulated genes being NRT1.3, NRT1.5, NRT2.1, NRT2.3, and NRT2.4. We concluded that GO exposure decreased the root uptake area and root activity, and decreased the expression of NRTs, which may have consequently suppressed the NO₃^- uptake rate, leading to adverse nitrate accumulation in stressed plants.

Graphene oxide and indole-3-acetic acid cotreatment regulates the root growth of Brassica napus L. via multiple phytohormone pathways

BACKGROUND

Studies have indicated that graphene oxide (GO) could regulated Brassica napus L. root growth via abscisic acid (ABA) and indole-3-acetic acid (IAA). To study the mechanism and interaction between GO and IAA further, B. napus L (Zhongshuang No. 9) seedlings were treated with GO and IAA accordance with a two factor completely randomized design.

RESULTS

GO and IAA cotreatment significantly regulated the root length, number of adventitious roots, and contents of IAA, cytokinin (CTK) and ABA. Treatment with 25 mg/L GO alone or IAA (> 0.5 mg/L) inhibited root development. IAA cotreatment enhanced the inhibitory role of GO, and the inhibition was strengthened with increased in IAA concentration. GO treatments caused oxidative stress in the plants. The ABA and CTK contents decreased; however, the IAA and gibberellin (GA) contents first increased but then decreased with increasing IAA concentration when IAA was combined with GO compared with GO alone. The 9-cis-epoxycarotenoid dioxygenase (NCED) transcript level strongly increased when the plants were treated with GO. However, the NCED transcript level and ABA concentration gradually decreased with increasing IAA concentration under GO and IAA cotreatment. GO treatments decreased the transcript abundance of steroid 5-alpha-reductase (DET2) and isochorismate synthase 1 (ICS), which are associated with brassinolide (BR) and salicylic acid (SA) biosynthesis, but increased the transcript abundance of brassinosteroid insensitive 1-associated receptor kinase 1 (BAK1), cam-binding protein 60-like G (CBP60) and calmodulin binding protein-like protein 1, which are associated with BR and SA biosynthesis. Last, GO treatment increased the transcript abundance of 1-aminocyclopropane-1-carboxylic acid synthase 2 (ACS2), which is associated with the ethylene (ETH) pathway.

CONCLUSIONS

Treatment with 25 mg/L GO or IAA (> 0.5 mg/L) inhibited root development. However, IAA and GO cotreatment enhanced the inhibitory role of GO, and this inhibition was strengthened with increased IAA concentration. IAA is a key factor in the response of B. napus L to GO and the responses of B. napus to GO and IAA cotreatment involved in multiple pathways, including those involving ABA, IAA, GA, CTK, BR, SA. Specifically, GO and IAA cotreatment affected the GA content in the modulation of B. napus root growth.