Role of cytokinin and auxin in shaping root architecture: regulating vascular differentiation, lateral root initiation, root apical dominance and root gravitropism

Impact of amino acid supplementation on hydroponic lettuce (Lactuca sativa L.) growth and nutrient content

Lettuce (Lactuca sativa L.), a widely cultivated leafy green, is valued for its rich content of bioactive compounds, including folates, vitamins, tocopherols, ascorbic acid, and antioxidants. This study aimed to evaluate the effects of amino acid supplementation on the growth and nutrient content of hydroponically grown lettuce. A greenhouse experiment using a completely randomized design (CRD) was conducted, with three replications and three plants per replication. There were 4 treatments (T0 (Control), T1 (Methionine 20 mg/L), T2 (Tryptophan 220 mg/L, T3 (Glycine 200 mg/L) of this experiment Growth parameters, including biomass, leaf length, leaf width, and leaf area, were measured four weeks after transplantation. L-methionine supplementation resulted in a significant improvement in plant growth, with a 23.60% increase in biomass and a 31.41% increase in leaf area. Conversely, L-tryptophan treatment led to substantial reductions in growth, including a 98.78% decrease in biomass. Nutrient analysis revealed that amino acid treatments, especially methionine, enhanced the nitrogen, phosphorus, and potassium content in leaf tissues. These results suggest that L-methionine has a positive effect on both growth and nutrient uptake in hydroponic lettuce, while L-tryptophan and L-glycine negatively affect plant development. The differential responses to amino acid treatments may be attributed to their distinct roles in plant metabolism, with methionine enhancing sulfur-containing compounds and proteins essential for growth, while tryptophan and glycine could disrupt metabolic pathways. Future research should explore the mechanisms underlying these effects and evaluate the optimal amino acid concentrations for maximizing hydroponic lettuce production and nutrient density.

Seed Endophytic Bacteria from Manilkara zapota L. and Their Influence as Rice Seed Priming Agents

In recent years, seed endophytes have gained significant attention due to their impact on the ecology, health, and productivity of host plants. Extensive research is being conducted to explore novel endophytic bacteria for sustainable crop improvement. Manilkara zapota L. P. Royen (Sapotaceae) is a highly stress-tolerant tree widely cultivated in tropical countries, yet its associated endophytes remain unexplored. In this study, nine bacterial isolates were obtained from M. zapota seeds, of which three (LA2, LA4, and NS1) were selected based on their IAA production capability which ranged from 2.3, 6.34, and 16.1 µg mL-1, respectively. Identification through 16S rRNA sequencing confirmed LA2 as Pseudomonas rhodesiae, LA4 as Bacillus cereus, and NS1 as Enterobacter cloacae. All isolates exhibited nitrogen-fixing ability, while NS1 uniquely solubilized potassium and phosphorus with KSI and PSI value as 2.9 and 2.3, respectively. Further, the efficacy of the bacterial isolates in promoting rice seedling growth was evaluated, and novel bioformulation was prepared from the consortia of LA2 + LA4, LA2 + NS1, LA4 + NS1, and LA2 + LA4 + NS1. All the isolates and bioformulations were tested as biopriming agents. Rice seedling growth experiments revealed a significant increase in germination percentage, root length, and shoot length following biopriming with individual isolates and consortia. Among treatments, the LA2 + LA4 combination exhibited the highest growth promotion, with a root length increase of 2.1-fold and shoot length increase of 2.3-fold as compared to control. Thus, our results highlighted that bioprospecting microbes from M. zapota seeds can help in nutrient management and seedling establishment.

Root system morphoanatomy of sunflower genotypes under water deficit

Sunflower is classified as a moderately drought tolerant crop. Genotypic variations and water availability are factors that influence the root development of the crop, which is important for water absorption in deep regions of the soil. Therefore, tests in controlled water deficit environments allow evaluating a set of morphoanatomical characteristics of the root system that attribute tolerance to water deficit, contributing to sunflower genetic improvement programs. The objective of this study was to identify a set of root morphoanatomical characteristics of four sunflower genotypes subjected to controlled water deficit. We tested four commercial sunflower genotypes (OLISUN03, AGUARÁ06, HELIO250 and BRS323) under well-irrigated (field capacity) and water restriction (40% of field capacity) conditions, completely randomized design with six replicates was applied, grown in rhizotron pot, allowing to evaluate root development through imaging and anatomical characteristics related to water absorption in different regions of the sunflower root system. Plants under water deficit showed changes that contributed to water absorption in different positions of root development. Under water deficit, the tissue differentiation occurred first near the root apex, while at field capacity differentiation occurred close to the root base. In the condition of water deficit, it was verified narrow root system architecture (RSA) for the genotype OLISUN03, deep RSA for BRS323, reduced endoderm thickness in OLISUN03 and vascular cylinder area in AGUARÁ06. In general, water deficit promoted changes in the morphological and anatomical characteristics of the root system. Morphological and anatomical modifications of the root system contribute to the anchoring and absorption of water and nutrients in places with little water availability in the soil.

Eco-friendly Biocontrol of Ralstonia solanacearum and Plant Growth Promotion in Tobacco Using Garbage Enzyme and Bacillus velezensis A1

Ralstonia solanacearum, the causative agent of bacterial wilt disease, poses a significant threat to agriculture. The demand for safe and high-quality food has increased interest in biological control agents (BCAs), despite challenges related to stability and cost. Garbage enzymes (GEs) are a promising alternative, rich in beneficial microbes and organic compounds. In this study, four types of GEs (onion, garlic, ginger, and mixed fruit) were individually tested against R. solanacearum in vitro, with only onion GE showing significant inhibition. Filtered onion GE, which lacked any microbes, also showed inhibition; however, its heat-treated form exhibited a reduced inhibitory effect, indicating the role of heat-sensitive compounds in inhibiting R. solanacearum. An antagonistic bacterial strain A1, isolated from onion GE, inhibited pathogen growth by up to 75% through volatile compounds. Cell-free culture filtrate of the strain A1 also inhibited R. solanacearum in vitro. Strain A1 exhibited nitrogen fixation, siderophore production, indole acetic acid (IAA) synthesis, and extracellular enzyme production, positioning it as a potent biocontrol agent. The genome analysis of the strain A1 revealed the presence of several plant growth-promoting genes. In vivo studies with GE, GE-filtered, and strain A1 demonstrated significant pathogen inhibition and promoted tobacco plant growth. Disease incidence was reduced to 26.6% with GE, 46.67% with microbe-free GE, and 40% with strain A1. Overall, these treatments positively impacted plant root and shoot lengths as well as both fresh and dry weights. Our findings highlight onion GE as a potential, environmentally friendly method for controlling bacterial wilt and enhancing plant development, offering an alternative approach to traditional chemical controls in agriculture.

Beneficial Effects of ACC Deaminase-Producing Rhizobacteria on the Drought Stress Resistance of Coffea arabica L

Given the challenges of climate change, effective adaptation strategies for crops like coffee are crucial. This study evaluated twelve 1-aminocyclopropane-1-carboxylate deaminase-producing bacterial strains selectively isolated from the rhizosphere of Coffea arabica L. cv. Costa Rica 95 in a plantation located in Veracruz, Mexico, focusing on their potential to enhance drought resistance. The strains, representing seven genera from the Gamma-proteobacteria and Bacteroidota groups, were characterized for growth-promoting traits, including ACC deaminase activity, indole-3-acetic acid (IAA) synthesis, phosphates solubilization, siderophore production, and nitrogen fixation. Strains of the genus Pantoea exhibited higher ACC deaminase activity, phosphate solubilization, and IAA synthesis, while others, such as Sphingobacterium and Chryseobacterium, showed limited plant growth-promoting traits. A pot experiment was conducted with coffee plants subjected to either full irrigation (soil with 85% volumetric water content) or drought (soil with 55% volumetric water content) conditions, along with inoculation with the isolated strains. Plants inoculated with Pantoea sp. RCa62 demonstrated improved growth metrics and physiological traits under drought, including higher leaf area, relative water content (RWC), biomass, and root development compared to uninoculated controls. Similar results were observed with Serratia sp. RCa28 and Pantoea sp. RCa31 under full irrigation conditions. Pantoea sp. RCa62 exhibited superior root development under stress, contributing to overall plant development. Proline accumulation was significantly higher in drought-stressed, non-inoculated plants compared to those inoculated with Pantoea sp. RCa62. This research highlights the potential of Pantoea sp. RCa62 to enhance coffee plant resilience to drought and underscores the need for field application and further validation of these bioinoculants in sustainable agricultural practices.

Comprehensive analysis of small RNA, transcriptome, and degradome sequencing: Mapping the miRNA-gene regulatory network for the development of sweet potato tuber roots

As an important starch crop, sweet potato has significant practical importance for maintaining food security worldwide. This study identified differential expressed genes associated with the expansion of tuberous roots by comparing the transcriptome across tuberous roots at the initial period (initiated tuberous roots (ITRs), rapid expansion period (tuberous roots (TRs), fibrous roots (FRs) at the seedling stage, and fibrous roots at the adult stage (unexpanded FRs (UFRs)). sRNA-seq and degradome analyses were performed to reveal the role of miRNAs in tuberous root development in sweet potato. A total of 29,633 genes and 510 miRNAs were differential expressed among FRs, ITRs, TRs, and UFRs. Integrated analyses of these data revealed genes involved in metabolism, hormone response, and signal transduction that might participate in the induction of tuberous root formation, while genes involved in carbohydrate and energy metabolism that might participate in the tuberous root swelling. A joint analysis of miRNAs and DEGs related to tuber development revealed by degradome-seq identified twelve miRNA-target gene pairs involved in gene expression process, hormone response, and metabolism of secondary metabolites that might be key regulators of root tuber development in sweet potato. Moreover, the functions of many miRNA-target gene pairs involved in the initiation of root tuber were related to auxin signaling response, and an exogenous hormone treatment experiment was further performed. The results indicated that auxin treatment had the most significant effect on increasing sweet potato yield, suggesting a dominant role of the auxin pathway in the regulation of sweet potato tuberous root development. Additionally, two miRNA-target pairs, miR319-TCP4 and miR172-AP2, which were identified from the degradome, were verified via 5' RNA ligase-mediated rapid amplification of cDNA ends (RLR-RACE) and tobacco transient cotransformation tests, and their expression was impacted by auxin treatment, which further validated the reliability of our multiomics analysis results. Our research provides new insights into the role of miRNAs in sweet potato root tuber development.

Root system architecture plasticity with beneficial rhizosphere microbes: Current findings and future perspectives

The rhizosphere microbiota, often referred to as the plant's "second genome" plays a critical role in modulating root system architecture (RSA). Despite this, existing methods to analyze root phenotypes in the context of root-microbe interactions remain limited, and the precise mechanisms affecting RSA by microbes are still not fully understood. This review comprehensively evaluates current root phenotyping techniques relevant to plant-microbe interactions, discusses their limitations, and explores future directions for integrating advanced technologies to elucidate microbial roles in altering RSA. Here, we summarized that microbial metabolite, primarily through auxin signaling pathways, drive root development changes. By harnessing advanced phenotyping tools, we aim to uncover more detailed mechanisms by which microbes modify RSA, providing valuable insights into strategies for optimizing nutrient uptake, bolstering food security, and enhancing resilience against climate-induced environmental stresses.

A lipid synthase maintains metabolic flux for jasmonate synthesis to regulate root growth and phosphate homeostasis

Plants require phosphate (Pi) for proper growth and development but often face scarcity of this vital nutrient in the soil. Pi starvation triggers membrane lipid remodeling to utilize the membrane phospholipid-bound Pi in plants. In this process, phospholipids are replaced by non-Pi-containing galactolipids (monogalactosyldiacylglycerol, MGDG; digalactosyldiacylglycerol, DGDG) and sulfolipids. The galactolipids ratio (MGDG:DGDG) is suggested to influence jasmonic acid (JA) biosynthesis. However, how the MGDG:DGDG ratio, JA levels, and root growth are coordinated under Pi deficiency in rice (Oryza sativa) remains unknown. Here, we characterized DGDG synthase 1 (OsDGD1) for its role in regulating root development by maintaining metabolic flux for JA biosynthesis. We showed that OsDGD1 is responsive under low Pi and is under the direct control of Phosphate Starvation Response 2, the master regulator of low Pi adaptations. Further, OsDGD1 knockout (KO) lines showed marked phenotypic differences compared to the wild type, including a significant reduction in root length and biomass, leading to reduced Pi uptake. Further, lipidome analyses revealed reduced DGDG levels in the KO line, leading to reduced membrane remodeling, thus affecting P utilization efficiency. We also observed an increase in the MGDG:DGDG ratio in KO lines, which enhanced the endogenous JA levels and signaling. This imbalance of JA in KO plants led to changes in auxin levels, causing drastic root growth inhibition. These findings indicate the critical role of OsDGD1 in maintaining optimum levels of JA during Pi deficiency for conducive root growth. Besides acting as signaling molecules and structural components, our study widens the role of lipids as metabolic flux controllers for phytohormone biosynthesis.

Identification of the AHP family reveals their critical response to cytokinin regulation during adventitious root formation in apple rootstock

Adventitious root (AR) formation is a bottleneck for vegetative proliferation. In this study, 13 AHP genes (MdAHPs) were identified in the apple genome. Phylogenetic analysis grouped them into 3 clusters (I, II, III), with 4, 4, and 5 genes respectively. The 13 MdAHPs family members were named MdAHP1 to MdAHP13 by chromosome positions. The physicochemical properties, phylogenetic relationship, motifs, and elements of their proteins were also analyzed. The amino acid quantity varied from 60~189 aa, isoelectric point lay between 4.10 and 8.93, and there were 3~7 protein-conserving motifs. Excluding MdAHP6, other members' promoter sequences behaved 2-4 CTK response elements. Additionally, the expression characteristics of MdAHPs family members at key stages of AR formation and in different tissues were also examined with exogenous 6-BA and Lov treatments. The results showed that MdAHP3 might be a key member in AR formation. GUS staining indicated that the activity of the MdAHP3 promoter was also significantly enhanced by CTK treatment. The protein interactions of MdAHP3/MdAHP1 and MdAHP3/MdAHP6 were verified. Compared with WT, 35S::MdAHP3 transgenic poplars inhibited AR formation. The above experimental results suggested that MdAHP3, as a key family member, interacts with MdAHP1 and MdAHP6 proteins to jointly mediate AR formation in apple rootstocks.

A nitrogen-responsive cytokinin oxidase/dehydrogenase regulates root response to high ammonium in rice

Plant root system is significantly influenced by high soil levels of ammonium nitrogen, leading to reduced root elongation and enhanced lateral root branching. In Arabidopsis, these processes have been reported to be mediated by phytohormones and their downstream signaling pathways, while the controlling mechanisms remain elusive in crops. Through a transcriptome analysis of roots subjected to high/low ammonium treatments, we identified a cytokinin oxidase/dehydrogenase encoding gene, CKX3, whose expression is induced by high ammonium. Knocking out CKX3 and its homologue CKX8 results in shorter seminal roots, fewer lateral roots, and reduced sensitivity to high ammonium. Endogenous cytokinin levels are elevated by high ammonium or in ckx3 mutants. Cytokinin application results in shorter seminal roots and fewer lateral roots in wild-type, mimicking the root responses of ckx3 mutants to high ammonium. Furthermore, CKX3 is transcriptionally activated by type-B RR25 and RR26, and ckx3 mutants have reduced auxin content and signaling in roots under low ammonium. This study identified RR25/26-CKX3-cytokinin as a signal module that mediates root responses to external ammonium by modulating of auxin signaling in the root meristem and lateral root primordium. This highlights the critical role of cytokinin metabolism in regulating rice root development in response to ammonium.

In Vitro vs. In Vivo Transcriptomic Approach Revealed Core Pathways of Nitrogen Deficiency Response in Tea Plant (Camellia sinensis (L.) Kuntze)

For the first time, we used an in vitro vs. in vivo experimental design to reveal core pathways under nitrogen deficiency (ND) in an evergreen tree crop. These pathways were related to lignin biosynthesis, cell redox homeostasis, the defense response to fungus, the response to Karrikin, amino acid transmembrane transport, the extracellular region, the cellular protein catabolic process, and aspartic-type endopeptidase activity. In addition, the mitogen-activated protein kinase pathway and ATP synthase (ATP)-binding cassette transporters were significantly upregulated under nitrogen deficiency in vitro and in vivo. Most of the MAPK downstream genes were related to calcium signaling (818 genes) rather than hormone signaling (157 genes). Moreover, the hormone signaling pathway predominantly contained auxin- and abscisic acid-related genes, indicating the crucial role of these hormones in ND response. Overall, 45 transcription factors were upregulated in both experiments, 5 WRKYs, 3 NACs, 2 MYBs, 2 ERFs, HD-Zip, RLP12, bHLH25, RADIALIS-like, and others, suggesting their ND regulation is independent from the presence of a root system. Gene network reconstruction displayed that these transcription factors participate in response to fungus/chitin, suggesting that nitrogen response and pathogen response have common regulation. The upregulation of lignin biosynthesis genes, cytochrome genes, and strigalactone response genes was much more pronounced under in vitro ND as compared to in vivo ND. Several cell wall-related genes were closely associated with cytochromes, indicating their important role in flavanols biosynthesis in tea plant. These results clarify the signaling mechanisms and regulation of the response to nitrogen deficiency in evergreen tree crops.

Gravitropic Gene Expression Divergence Associated With Adaptation to Contrasting Environments in an Australian Wildflower

Plants adapt to their local environment through complex interactions between genes, gene networks and hormones. Although the impact of gene expression on trait regulation and evolution has been recognised for many decades, its role in the evolution of adaptation is still a subject of intense exploration. We used a Multi-parent Advanced Generation Inter-Cross (MAGIC) population, which we derived from crossing multiple parents from two distinct coastal ecotypes of an Australia wildflower, Senecio lautus. We focused on studying the contrasting gravitropic behaviours of these ecotypes, which have evolved independently multiple times and show strong responses to natural selection in field experiments, emphasising the role of natural selection in their evolution. Here, we investigated how gene expression differences have contributed to the adaptive evolution of gravitropism. We studied gene expression in 60 pools at five time points (30, 60, 120, 240 and 480 min) after rotating half of the pools 90°. We found 428 genes with differential expression in response to the 90° rotation treatment. Of these, 81 genes (~19%) have predicted functions related to the plant hormones auxin and ethylene, which are crucial for the gravitropic response. By combining insights from Arabidopsis mutant studies and analysing our gene networks, we propose a preliminary model to explain the differences in gravitropism between ecotypes. This model suggests that the differences arise from changes in the transport and availability of the two hormones auxin and ethylene. Our findings indicate that the genetic basis of adaptation involves interconnected signalling pathways that work together to give rise to new ecotypes.

Systemic strategies for cytokinin biosynthesis and catabolism in Arabidopsis roots and leaves under prolonged ammonium nutrition

Cytokinins are growth-regulating plant hormones that are considered to adjust plant development under environmental stresses. During sole ammonium nutrition, a condition known to induce growth retardation of plants, altered cytokinin content can contribute to the characteristic ammonium toxicity syndrome. To understand the metabolic changes in cytokinin pools, cytokinin biosynthesis and degradation were analyzed in the leaves and roots of mature Arabidopsis plants. We found that in leaves of ammonium-grown plants, despite induction of biosynthesis on the expression level, there was no active cytokinin build-up because they were effectively routed toward their downstream catabolites. In roots, cytokinin conjugation was also induced, together with low expression of major synthetic enzymes, resulting in a decreased content of the trans-zeatin form under ammonium conditions. Based on these results, we hypothesized that in leaves and roots, cytokinin turnover is the major regulator of the cytokinin pool and does not allow active cytokinins to accumulate. A potent negative-regulator of root development is trans-zeatin, therefore its low level in mature root tissues of ammonium-grown plants may be responsible for occurrence of a wide root system. Additionally, specific cytokinin enhancement in apical root tips may evoke a short root phenotype in plants under ammonium conditions. The ability to flexibly regulate cytokinin metabolism and distribution in root and shoot tissues can contribute to adjusting plant development in response to ammonium stress.

Hydrotropism mechanisms and their interplay with gravitropism

Plants partly optimize their water recruitment from the growth medium by directing root growth toward a moisture source, a phenomenon termed hydrotropism. The default mechanism of downward growth, termed gravitropism, often functions to counteract hydrotropism when the water-potential gradient deviates from the gravity vector. This review addresses the identity of the root sites in which hydrotropism-regulating factors function to attenuate gravitropism and the interplay between these various factors. In this context, the function of hormones, including auxin, abscisic acid, and cytokinins, as well as secondary messengers, calcium ions, and reactive oxygen species in the conflict between these two opposing tropisms is discussed. We have assembled the available data on the effects of various chemicals and genetic backgrounds on both gravitropism and hydrotropism, to provide an up-to-date perspective on the interactions that dictate the orientation of root tip growth. We specify the relevant open questions for future research. Broadening our understanding of root mechanisms of water recruitment holds great potential for providing advanced approaches and technologies that can improve crop plant performance under less-than-optimal conditions, in light of predicted frequent and prolonged drought periods due to global climate change.

The Receptor Kinases DRUS1 and DRUS2 Behave Distinctly in Osmotic Stress Tolerance by Modulating the Root System Architecture via Auxin Signaling

Receptor kinases DRUS1 (Dwarf and Runtish Spikelet1) and DRUS2 are orthologues of the renowned Arabidopsis thaliana gene FERONIA, which play redundant roles in rice growth and development. Whether the two duplicated genes perform distinct functions in response to environmental stress is largely unknown. Here, we found that osmotic stress (OS) and ABA increased DRUS1 expression while decreasing DRUS2. When subjected to osmotic stress, the increased DRUS1 in drus2 mutants suppresses the OsIAA repressors, resulting in a robust root system with an increased number of adventitious and lateral roots as well as elongated primary, adventitious, and lateral roots, conferring OS tolerance. In contrast, the decreased DRUS2 in drus1-1 mutants are not sufficient to suppress OsIAA repressors, leading to a feeble root system with fewer adventitious and lateral roots and hindering seminal root growth, rendering OS intolerance. All these findings offer valuable insights into the biological significance of the duplication of two homologous genes in rice, wherein, if one is impaired, the other one is able to continue auxin-signaling-mediated root growth and development to favor resilience to environmental stress, such as water shortage.

Exogenous Cytokinin Induces Callus and Protocorm-Like-Bodies Formation in In Vitro Root Tips of Vanilla planifolia Andrews

Vanilla is a popular flavouring essence derived from the pods of vanilla orchid plants. Due to the high demand for vanilla flavour, high yielding vanilla plantlets are necessary for establishing vanilla plantations. Clonal micropropagation is a viable technique for the mass production of high yielding vanilla plantlets. This study reports an efficient regeneration protocol by using cytokinin as the sole plant growth regulator to regenerate plantlets from the root tips of a commercial vanilla orchid species, Vanilla planifolia. Most studies to date have reported using seeds and nodes as starting explants for in vitro micropropagation of vanilla orchids. So far, regeneration from roots has not been very successful. Previous studies favoured the use of auxins only or high auxin to cytokinin ratios to induce callus, and sole cytokinins were used for direct shoot regeneration. However, it was sporadically observed in plantlets regeneration of V. planifolia that multiple shoots were regenerated from the tips of intact aerial roots submerged in media. This study therefore investigated the regeneration of excised vanilla root tips through the application of most commonly used auxins (1-naphthaleneacetic acid and 2,4-dichlorophenoxyacetic acid) and cytokinins (6-benzylaminopurine and thidiazuron). High auxin presence is known to promote callusing in in vitro plants. However, in this study, auxin treatment inhibits callusing in root tips. While cytokinin treatments, even at low levels, has promoted high rate of callusing. These callus cells regenerate into protocorm-like-body (PLB) shoots when cytokinin levels are increased to 0.5 mg/mL 6-benzylaminopurine (BAP) under light conditions. The findings of the study have the potential of providing large quantity of high yielding vanilla plantlets through clonal micropropagation.

Using microalgae to reduce the use of conventional fertilizers in hydroponics and soil-based cultivation

The intensive use of agrochemicals has led to nutrient loss, greenhouse gas emissions, and resource depletion, thus the development of sustainable agricultural solutions is required. Microalgal biomass has the potential to provide nutrients such as nitrogen, phosphorus, and potassium, along with various plant growth promoters, to enhance crop productivity and impart disease resistance. This study provides a comprehensive assessment of the potential applications of microalgal extracts and biomass in the contexts of seed germination, hydroponic systems, and soil-based crop cultivation. The results revealed that the extracts from Chlorella sp. and Anabaena sp. have no significant impact on the germination of wheat seeds. High concentrations of Chlorella sp. and Anabaena sp. cell extracts in hydroponics enhanced the length of cucumber seedling stems by 81.7 % and 58.3 %, respectively. Additionally, the use of microalgal cell extracts hindered root elongation while stimulating the growth of lateral and fibrous roots. Furthermore, the study compared the performance of 5 different fertilizers: 1) inorganic fertilizer (IF), 2) organic fertilizer (OF), 3) microalgae-based biofertilizer (MF), 4) inorganic fertilizer + microalgae-based biofertilizer (IM), 5) organic fertilizer + microalgae-based biofertilizer (OM). The findings indicate that the plant growth and soil physicochemical properties in the groups supplied with different fertilizers are comparable and significantly higher than those in the control group. The levels of protein, chlorophyll A, and chlorophyll B in the MF group increased significantly by 40 %, 29.2 %, and 33.5 %, respectively, compared to the control group. However, it remained notably lower compared to groups supplied with inorganic and organic fertilizers (p < 0.05). Combining microalgae with organic fertilizer can simultaneously enhance the yield and quality of Chinese cabbage, representing a promising source of crop nutrition. In conclusion, this study suggests that it is promising to use microalgae to reduce the use of conventional fertilizers in hydroponics and soil-based cultivation.

Identification of genetics and hormonal factors involved in Quercus robur root growth regulation in different cultivation system

Understanding the molecular processes and hormonal signals that govern root growth is of paramount importance for effective forest management. While Arabidopsis studies have shed light on the role of the primary root in root system development, the structure of root systems in trees is considerably more intricate, posing challenges to comprehend taproot growth in acorn-sown and nursery-cultivated seedlings. In this study, we investigated Quercus robur seedlings using rhizotrons, containers, and transplanted containers to rhizotrons, aiming to unravel the impact of forest nursery practices on processes governing taproot growth and root system development. Root samples were subjected to RNA-seq analysis to identify gene expression patterns and perform differential gene expression and phytohormone analysis. Among studied cultivation systems, differentially expressed genes (DEGs) exhibited significant diversity, where the number of co-occurring DEGs among cultivation systems was significantly smaller than the number of unique DEGs in different cultivation systems. Moreover, the results imply that container cultivation triggers the activation of several genes associated with linolenic acid and peptide synthesis in root growth. Upon transplantation from containers to rhizotrons, rapid enhancement in gene expression occurs, followed by gradual reduction as root growth progresses, ultimately reaching a similar expression pattern as observed in the taproot of rhizotron-cultivated seedlings. Phytohormone analysis revealed that taproot growth patterns under different cultivation systems are regulated by the interplay between auxin and cytokinin concentrations. Moreover, the diversification of hormone levels within the root zone and cultivation systems allows for taproot growth inhibition and prompt recovery in transplanted seedlings. Our study highlights the crucial role of hormone interactions during the early stages of taproot elongation, influencing root system formation across.

S1 basic leucine zipper transcription factors shape plant architecture by controlling C/N partitioning to apical and lateral organs

Plants tightly control growth of their lateral organs, which led to the concept of apical dominance. However, outgrowth of the dormant lateral primordia is sensitive to the plant's nutritional status, resulting in an immense plasticity in plant architecture. While the impact of hormonal regulation on apical dominance is well characterized, the prime importance of sugar signaling to unleash lateral organ formation has just recently emerged. Here, we aimed to identify transcriptional regulators, which control the trade-off between growth of apical versus lateral organs. Making use of locally inducible gain-of-function as well as single and higher-order loss-of-function approaches of the sugar-responsive S1-basic-leucine-zipper (S1-bZIP) transcription factors, we disclosed their largely redundant function in establishing apical growth dominance. Consistently, comprehensive phenotypical and analytical studies of S1-bZIP mutants show a clear shift of sugar and organic nitrogen (N) allocation from apical to lateral organs, coinciding with strong lateral organ outgrowth. Tissue-specific transcriptomics reveal specific clade III SWEET sugar transporters, crucial for long-distance sugar transport to apical sinks and the glutaminase GLUTAMINE AMIDO-TRANSFERASE 1_2.1, involved in N homeostasis, as direct S1-bZIP targets, linking the architectural and metabolic mutant phenotypes to downstream gene regulation. Based on these results, we propose that S1-bZIPs control carbohydrate (C) partitioning from source leaves to apical organs and tune systemic N supply to restrict lateral organ formation by C/N depletion. Knowledge of the underlying mechanisms controlling plant C/N partitioning is of pivotal importance for breeding strategies to generate plants with desired architectural and nutritional characteristics.

Humic acid improves wheat growth by modulating auxin and cytokinin biosynthesis pathways

Humic acids have been widely used for centuries to enhance plant growth and productivity. The beneficial effects of humic acids have been attributed to different functional groups and phytohormone-like compounds enclosed in macrostructure. However, the mechanisms underlying the plant growth-promoting effects of humic acids are only partially understood. We hypothesize that the bio-stimulatory effect of humic acids is mainly due to the modulation of innate pathways of auxin and cytokinin biosynthesis in treated plants. A physiological investigation along with molecular characterization was carried out to understand the mechanism of bio-stimulatory effects of humic acid. A gene expression analysis was performed for the genes involved in auxin and cytokinin biosynthesis pathways in wheat seedlings. Furthermore, Arabidopsis thaliana transgenic lines generated by fusing the auxin-responsive DR5 and cytokinin-responsive ARR5 promoter to ß-glucuronidase (GUS) reporter were used to study the GUS expression analysis in humic acid treated seedlings. This study demonstrates that humic acid treatment improved the shoot and root growth of wheat seedlings. The expression of several genes involved in auxin (Tryptophan Aminotransferase of Arabidopsis and Gretchen Hagen 3.2) and cytokinin (Lonely Guy3) biosynthesis pathways were up-regulated in humic acid-treated seedlings compared to the control. Furthermore, GUS expression analysis showed that bioactive compounds of humic acid stimulate endogenous auxin and cytokinin-like activities. This study is the first report in which using ARR5:GUS lines we demonstrate the biostimulants activity of humic acid.

FvemiR160-FveARF18A-FveAP1/FveFUL module regulates flowering time in woodland strawberry

Flowering is an indicator of plant transformation from vegetative to reproductive growth. miR160 has been shown to have a significant effect on the growth and development of fruits, leaves, and roots of plants or their stress response to environment, but the participation of miR160 in regulating flowering time in plants is unclear. In this study, we found that two FvemiR160s (FvemiR160a/FvemiR160b) mature sequences in strawberry (Fragaria vesca) were consistent. It was displayed that the miR160 mature sequence is highly conserved in various species, and the miR160 mature sequence formed by the 5' arm of the MIR160 precursor was more conserved. Three FveARFs in woodland strawberry were negatively regulated by FvemiR160a, among which FveARF18A was the most significant. Phylogenetic analysis indicated that FvemiR160 is closely related to apple (Malus domestica), grape (Vitis vinifera), and Arabidopsis thaliana, while FveARF18A is closely related to RcARF18. Subsequently, we demonstrated that FvemiR160a can target cutting FveARF18A to negatively regulate its expression by RLM-5' RACE, cleavage site mutation, and GFP fluorescence assay. Moreover, we observed that FveMIR160a overexpressed plants have advanced flowering, while mFveARF18A overexpressed plants have delayed flowering. We also verified that FveARF18A negatively regulates the expression of FveAP1 and FveFUL by binding their promoters by yeast one-hybrid, LUC, and GUS assay, and FveAP1 and FveFUL transgenic Arabidopsis showed early flowering phenotype. In addition, the expression level of FvemiR160a was decreased obviously while that of FveARF18A was increased obviously by MeJA, GA and IAA. In conclusion, our study reveals the important role of the FvemiR160-FveARF18A-FveAP1/FveFUL module in the flowering process of woodland strawberry and provides a new pathway for studying flowering.

Genome-wide identification and expression profiles analysis of the authentic response regulator gene family in licorice

Introduction

As one of the traditional Chinese medicinal herbs that were most generally used, licorice attracts lots of interest due to its therapeutic potential. Authentic response regulators (ARRs) are key factors in cytokinin signal transduction and crucial for plant growth and stress response processes. Nevertheless, the characteristics and functions of the licorice ARR genes are still unknown.

Results

In present study, a systematic genome-wide identification and expression analysis of the licorice ARR gene family were conducted and 51 ARR members were identified. Collinearity analysis revealed the significant roles of segmental duplications in the expansion of licorice ARR genes. The cis-acting elements associated with development, stress and phytohormone responses were identified, implying their pivotal roles in diverse regulatory processes. RNA-seq and qRT-PCR results suggested that A-type, but not B-type ARRs were induced by zeatin. Additionally, ARRs participated in diverse abiotic stresses and phytohormones responses. Yeast one-hybrid assay demonstrated that GuARR1, GuARR2, GuARR11, GuARR12, GuARR10-1, GuARR10-2 and GuARR14 were able to bind to the promoter of GuARR8-3, and GuARR1, GuARR12 bound to the GuARR8-1 promoter. GuARR1, GuARR2, GuARR11 and GuARR10-2 bound to the GuARR6-2 promoter as well as GuARR12 and GuARR10-2 bound to the GuARR6-1 promoter.

Discussion

Collectively, these findings provide a basis for future ARR genes function investigations, shedding light on the potential medicinal properties and agricultural applications of licorice.

Signal communication during microbial modulation of root system architecture

Every living organism on Earth depends on its interactions with other organisms. In the rhizosphere, plants and microorganisms constantly exchange signals and influence each other's behavior. Recent studies have shown that many beneficial rhizosphere microbes can produce specific signaling molecules that affect plant root architecture and therefore could have substantial effects on above-ground growth. This review examines these chemical signals and summarizes their mechanisms of action, with the aim of enhancing our understanding of plant-microbe interactions and providing references for the comprehensive development and utilization of these active components in agricultural production. In addition, we highlight future research directions and challenges, such as searching for microbial signals to induce primary root development.

A conserved graft formation process in Norway spruce and Arabidopsis identifies the PAT gene family as central regulators of wound healing

The widespread use of plant grafting enables eudicots and gymnosperms to join with closely related species and grow as one. Gymnosperms have dominated forests for over 200 million years, and despite their economic and ecological relevance, we know little about how they graft. Here we developed a micrografting method in conifers using young tissues that allowed efficient grafting with closely related species and between distantly related genera. Conifer graft junctions rapidly connected vasculature and differentially expressed thousands of genes including auxin and cell-wall-related genes. By comparing these genes to those induced during Arabidopsis thaliana graft formation, we found a common activation of cambium, cell division, phloem and xylem-related genes. A gene regulatory network analysis in Norway spruce (Picea abies) predicted that PHYTOCHROME A SIGNAL TRANSDUCTION 1 (PAT1) acted as a core regulator of graft healing. This gene was strongly up-regulated during both spruce and Arabidopsis grafting, and Arabidopsis mutants lacking PAT genes failed to attach tissues or successfully graft. Complementing Arabidopsis PAT mutants with the spruce PAT1 homolog rescued tissue attachment and enhanced callus formation. Together, our data show an ability for young tissues to graft with distantly related species and identifies the PAT gene family as conserved regulators of graft healing and tissue regeneration.

Structures and mechanisms of the Arabidopsis cytokinin transporter AZG1

Cytokinins are essential for plant growth and development, and their tissue distributions are regulated by transmembrane transport. Recent studies have revealed that members of the 'Aza-Guanine Resistant' (AZG) protein family from Arabidopsis thaliana can mediate cytokinin uptake in roots. Here we present 2.7 to 3.3 Å cryo-electron microscopy structures of Arabidopsis AZG1 in the apo state and in complex with its substrates trans-zeatin (tZ), 6-benzyleaminopurine (6-BAP) or kinetin. AZG1 forms a homodimer and each subunit shares a similar topology and domain arrangement with the proteins of the nucleobase/ascorbate transporter (NAT) family. These structures, along with functional analyses, reveal the molecular basis for cytokinin recognition. Comparison of the AZG1 structures determined in inward-facing conformations and predicted by AlphaFold2 in the occluded conformation allowed us to propose that AZG1 may carry cytokinins across the membrane through an elevator mechanism.

Methylobacterium spp. mitigation of UV stress in mung bean (Vigna radiata L.)

Methylotrophs are a diverse group of bacteria that abundantly colonize the phyllosphere and have great potential to withstand UV irradiation because of their pigmented nature and ability to promote plant growth through various mechanisms. The present study investigated the effects of UVB radiation on plant growth-promoting (PGP) properties of methylotrophic bacteria and the growth of Vigna radiata L. A total of 55 methylotrophic bacteria were isolated from desert plants, and 15 methylotrophs were resistant to UVB radiation for 4 h. All UVB-resistant methylotrophs possess a methyldehydrogenase gene. Identification based on 16S rRNA gene sequencing revealed that all 15 UVB-resistant methylotrophs belonged to the genera Methylorubrum (07), Methylobacterium (07), and Rhodococcus (01). Screening of methylotrophs for PGP activity in the presence and absence of UVB radiation revealed that all isolates showed ACC deaminase activity and growth on a nitrogen-free medium. Furthermore, the production of IAA-like substances ranged from 8.62 to 85.76 µg/mL, siderophore production increased from 3.47 to 65.75% compared to the control. Seed germination assay with V. radiata L. (mung bean) exposed to UVB radiation revealed that methylotrophs improved seed germination, root length, and shoot length compared to the control. The present findings revealed that the isolates SD3, SD2, KD1, KD5, UK1, and UK3 reduced the deleterious effects of UVB radiation on mung bean plants and can be used to protect seedlings from UVB radiation for sustainable agriculture.

Characterization of endophytic bacteria isolated from root nodules of lentil in intercropping with durum wheat

Legumes improve soil fertility by interacting symbiotically with nitrogen-fixing rhizobia allocated in root nodules. Some bacterial endophytes can coexist with rhizobia in nodules and might help legumes by enhancing stress tolerance, producing hormones stimulating plant growth, and increasing plant nutrient intake. Twenty-six bacterial endophytes from Lens culinaris root nodules cultivated in intercropping with Triticum durum were identified and characterized molecularly and biochemically. Potential plant growth-promoting strains have been selected according to the indole acetic acid and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase production, and for their inorganic phosphate solubilization ability. The presence of genes associated to ACC deaminase and nitrogenase was evaluated. Six selected strains were grown with varying NaCl and polyethylene glycol concentrations to test their salt and osmotic stress tolerance. Priestia megaterium 11NL3 and Priestia aryabhattai 19NL1, resulted to be tolerant to salinity and osmotic stress, were tested on four genotypes of T. durum seeds in different stress conditions. The effect of strain inoculation on seed germination, vigor, and root-to-shoot ratio varied depending on the type of stress and on the durum wheat genotypes. For future research, it will be necessary to test the selected bacterial strains at different plant phenological stages and to clarify the mechanisms involved in the different outcomes of plant-microbe interactions.

Mismatch between primary and secondary growth and its consequences on wood formation in Qinghai spruce

The connections between the primary and secondary growth of trees allows better understanding of the dynamics of carbon sequestration in forest ecosystems. The relationship between primary and secondary growth of trees could change due to the diverging responses of meristems to climate warming. In this study, the bud phenology and radial growth dynamics of Qinghai spruce (Picea crassifolia) in arid and semi-arid areas of China in 2019 and 2020 were weekly monitored to analyze their response to different weather conditions and their links with carbon sink. Xylem anatomical traits (i.e. lumen radial diameter and cell wall thickness) were quantified along cell radial files after the end of xylem lignification to calculate the early-to-latewood transition date. Winter and early spring (January-March) were warmer in 2020 with a colder April compared with 2019. Precipitation in April-June was lower in 2020 than in 2019. In 2019, bud phenology occurred earlier, while the onset of xylem formation and the early-to-latewood transition date were delayed. The duration from the beginning of split bud and exposed shoot to the early-to-latewood transition date was positively correlated with the radial width of earlywood (accounting for ~80% of xylem width) and total xylem width. The longer duration of xylem cell division did not increase xylem cell production and radial width. Moreover, the duration from bud burst to the early-to-latewood transition date in 2020 was negatively linked with early phloem cell production as compared with 2019. Our findings suggest that warm conditions in winter and early spring promote the xylogenesis of Qinghai spruce, but might delay bud burst. However, the xylem width increments largely depend on the duration from bud burst to the start of latewood cell division rather than on the earlier xylogenesis and longer duration of xylem cell differentiation induced by warm conditions.

Multifarious Characterization and Efficacy of Three Phosphate-Solubilizing Aspergillus Species as Biostimulants in Improving Root Induction of Cassava and Sugarcane Stem Cuttings

Several soil fungi significantly contribute to the enhancement of plant development by improving nutrient uptake and producing growth-promoting metabolites. In the present study, three strains of phosphate-solubilizing fungi, namely, Aspergillus chiangmaiensis SDBR-CMUI4, A. pseudopiperis SDBR-CMUI1, and A. pseudotubingensis SDBR-CMUO2, were examined for their plant-growth-promoting capabilities. The findings demonstrated that all fungi showed positive siderophore production, but only A. pseudopiperis can produce indole-3-acetic acid. All fungi were able to solubilize insoluble phosphate minerals [Ca3(PO4)2 and FePO4] by producing phosphatase enzymes and organic acids (oxalic, tartaric, and succinic acids). These three fungal species were grown at a water activity ranging from 0.837 to 0.998, pH values ranging from 4 to 9, temperatures between 4 and 40 °C, and 16-17% NaCl in order to evaluate their drought, pH, temperature, and salt tolerances, respectively. Moreover, the results indicated that A. pseudopiperis and A. pseudotubingensis were able to tolerate commercial insecticides (methomyl and propargite) at the recommended dosages for field application. The viability of each fungal strain in the inoculum was higher than 50% at 4 and 20 °C after 3 months of storage. Subsequently, all fungi were characterized as plant-growth-promoting strains by improving the root inductions of cassava (Manihot esculenta Crantz) and sugarcane (Saccharum officinarum L.) stem cuttings in greenhouse experiments. No symptoms of plant disease were observed with any of the treatments involving fungal inoculation and control. The cassava and sugarcane stem cuttings inoculated with fungal strains and supplemented with Ca3(PO4)2 exhibited significantly increased root lengths, shoot and root dry biomasses, chlorophyll concentrations, and cellular inorganic phosphate contents. Therefore, the application of these phosphate-solubilizing fungi is regarded as a new frontier in the induction of roots and the promotion of growth in plants.

The role of plant growth promoting rhizobacteria in plant drought stress responses

Climate change has exacerbated the effects of abiotic stresses on plant growth and productivity. Drought is one of the most important abiotic stress factors that interfere with plant growth and development. Plant selection and breeding as well as genetic engineering methods used to improve crop drought tolerance are expensive and time consuming. Plants use a myriad of adaptative mechanisms to cope with the adverse effects of drought stress including the association with beneficial microorganisms such as plant growth promoting rhizobacteria (PGPR). Inoculation of plant roots with different PGPR species has been shown to promote drought tolerance through a variety of interconnected physiological, biochemical, molecular, nutritional, metabolic, and cellular processes, which include enhanced plant growth, root elongation, phytohormone production or inhibition, and production of volatile organic compounds. Therefore, plant colonization by PGPR is an eco-friendly agricultural method to improve plant growth and productivity. Notably, the processes regulated and enhanced by PGPR can promote plant growth as well as enhance drought tolerance. This review addresses the current knowledge on how drought stress affects plant growth and development and describes how PGPR can trigger plant drought stress responses at the physiological, morphological, and molecular levels.

The changes in the maize root cell walls after exogenous application of auxin in the presence of cadmium

Cadmium (Cd) is a transition metal and hazardous pollutant that has many toxic effects on plants. This heavy metal poses a health risk for both humans and animals. The cell wall is the first structure of a plant cell that is in contact with Cd; therefore, it can change its composition and/or ratio of wall components accordingly. This paper investigates the changes in the anatomy and cell wall architecture of maize (Zea mays L.) roots grown for 10 days in the presence of auxin indole-3-butyric acid (IBA) and Cd. The application of IBA in the concentration 10-9 M delayed the development of apoplastic barriers, decreased the content of lignin in the cell wall, increased the content of Ca2+ and phenols, and influenced the composition of monosaccharides in polysaccharide fractions when compared to the Cd treatment. Application of IBA improved the Cd2+ fixation to the cell wall and increased the endogenous concentration of auxin depleted by Cd treatment. The proposed scheme from obtained results may explain the possible mechanisms of the exogenously applied IBA and its effects on the changes in the binding of Cd2+ within the cell wall, and on the stimulation of growth that resulted in the amelioration of Cd stress.

Perspectives on Computation in Plants

Plants thrive in virtually all natural and human-adapted environments and are becoming popular models for developing robotics systems because of their strategies of morphological and behavioral adaptation. Such adaptation and high plasticity offer new approaches for designing, modeling, and controlling artificial systems acting in unstructured scenarios. At the same time, the development of artifacts based on their working principles reveals how plants promote innovative approaches for preservation and management plans and opens new applications for engineering-driven plant science. Environmentally mediated growth patterns (e.g., tropisms) are clear examples of adaptive behaviors displayed through morphological phenotyping. Plants also create networks with other plants through subterranean roots-fungi symbiosis and use these networks to exchange resources or warning signals. This article discusses the functional behaviors of plants and shows the close similarities with a perceptron-like model that could act as a behavior-based control model in plants. We begin by analyzing communication rules and growth behaviors of plants; we then show how we translated plant behaviors into algorithmic solutions for bioinspired robot controllers; and finally, we discuss how those solutions can be extended to embrace original approaches to networking and robotics control architectures.

Bambara Nut Root-Nodules Bacteria from a Semi-Arid Region of South Africa and Their Plant Growth-Promoting Traits

Rhizobial nitrogen-fixing bacteria are the main inhabitants of the root nodules of legume plants. Studying the bacterial community of legume nodules is important in understanding plant growth and nutrient requirements. Culture-based technique was used to examine the bacterial community of these underground organs from Vigna subterranea L. Verdc (Bambara nut), an underutilized legume in Africa, for plant growth-promoting traits. In this study, Bambara nuts were planted to trap root-nodule bacteria, and the bacteria were morphologically, biochemically, and molecularly characterized. Five selected isolates were screened in vitro for their plant growth-promoting traits and exhibited differences in their phenotypic traits. The polymerase chain reaction (PCR) products were subjected to partial 16S rRNA gene sequencing for phylogenetic analysis. Based on 16S rRNA gene sequence, the isolates were identified as BA1 (Stenotrophomonas maltophilia), BA2 (Chryseobacterium sp.), BA3 (Pseudomonas alcaligenes), BA4 (Pseudomonas plecoglossicida), and BA5 (Pseudomonas hibiscicola). Results showed that four of the five isolates could produce IAA. The capability to solubilize phosphate in Pikovskaya's agar plates was positively shown by four isolates (BA2, BA3, BA4, and BA5). Three isolates could produce hydrogen cyanide while isolates BA1, BA3, BA4, and BA5 were found to have ammonia-production traits. The results suggest that these plant growth-promoting isolates can be used as inoculants for plant growth and productivity.

The Contribution of PGPR in Salt Stress Tolerance in Crops: Unravelling the Molecular Mechanisms of Cross-Talk between Plant and Bacteria

Soil salinity is a major abiotic stress in global agricultural productivity with an estimated 50% of arable land predicted to become salinized by 2050. Since most domesticated crops are glycophytes, they cannot be cultivated on salt soils. The use of beneficial microorganisms inhabiting the rhizosphere (PGPR) is a promising tool to alleviate salt stress in various crops and represents a strategy to increase agricultural productivity in salt soils. Increasing evidence underlines that PGPR affect plant physiological, biochemical, and molecular responses to salt stress. The mechanisms behind these phenomena include osmotic adjustment, modulation of the plant antioxidant system, ion homeostasis, modulation of the phytohormonal balance, increase in nutrient uptake, and the formation of biofilms. This review focuses on the recent literature regarding the molecular mechanisms that PGPR use to improve plant growth under salinity. In addition, very recent -OMICs approaches were reported, dissecting the role of PGPR in modulating plant genomes and epigenomes, opening up the possibility of combining the high genetic variations of plants with the action of PGPR for the selection of useful plant traits to cope with salt stress conditions.

Sucrose-induced auxin conjugate hydrolase restores symbiosis in a Medicago cytokinin perception mutant

Rhizobia-legume interactions recruit cytokinin for the induction of nodule primordia in the cortex. Cytokinin signaling regulates auxin transport and biosynthesis, causing local auxin accumulation, which triggers cortical cell division. Since sugar signaling can trigger auxin responses, we explored whether sugar treatments could rescue symbiosis in the Medicago truncatula cytokinin response 1 (cre1) mutant. Herein, we demonstrate that sucrose and its nonmetabolizable isomer turanose can trigger auxin response and recover functional symbiosis in cre1, indicating sucrose signaling to be necessary for the restoration of symbiosis. In both M. truncatula A17 (wild type) and cre1, sucrose signaling significantly upregulated IAA-Ala Resistant 3 (IAR33), encoding an auxin conjugate hydrolase, in rhizobia-infected as well as in uninfected roots. Knockdown of IAR33 (IAR33-KD) significantly reduced nodulation in A17, highlighting the importance of deconjugation-mediated auxin accumulation during nodule inception. In cre1, IAR33-KD restricted the sucrose-mediated restoration of functional symbiosis, suggesting that deconjugation-mediated auxin accumulation plays a key role in the absence of CRE1-mediated auxin biosynthesis and transport control. Overexpression of IAR33 also restored functional symbiosis in cre1, further suggesting that IAR33 mediates auxin accumulation in response to sucrose signaling. Since all the observed sucrose-mediated responses were common to A17 and cre1, deconjugation-mediated auxin response appeared to be independent of CRE1, which normally governs local auxin accumulation in the presence of rhizobia. We propose that sucrose-dependent restoration of symbiosis in cre1 occurs by the activation of IAR33-mediated auxin deconjugation.

Application of Data Modeling, Instrument Engineering and Nanomaterials in Selected Medid the Scientific Recinal Plant Tissue Culture

At present, most precious compounds are still obtained by plant cultivation such as ginsenosides, glycyrrhizic acid, and paclitaxel, which cannot be easily obtained by artificial synthesis. Plant tissue culture technology is the most commonly used biotechnology tool, which can be used for a variety of studies such as the production of natural compounds, functional gene research, plant micropropagation, plant breeding, and crop improvement. Tissue culture material is a basic and important part of this issue. The formation of different plant tissues and natural products is affected by growth conditions and endogenous substances. The accumulation of secondary metabolites are affected by plant tissue type, culture method, and environmental stress. Multi-domain technologies are developing rapidly, and they have made outstanding contributions to the application of plant tissue culture. The modes of action have their own characteristics, covering the whole process of plant tissue from the induction, culture, and production of natural secondary metabolites. This paper reviews the induction mechanism of different plant tissues and the application of multi-domain technologies such as artificial intelligence, biosensors, bioreactors, multi-omics monitoring, and nanomaterials in plant tissue culture and the production of secondary metabolites. This will help to improve the tissue culture technology of medicinal plants and increase the availability and the yield of natural metabolites.

Chromosome groups 5, 6 and 7 harbor major quantitative trait loci controlling root traits in bread wheat (Triticum aestivum L.)

Identifying genomic regions for root traits in bread wheat can help breeders develop climate-resilient and high-yielding wheat varieties with desirable root traits. This study used the recombinant inbred line (RIL) population of Synthetic W7984 × Opata M85 to identify quantitative trait loci (QTL) for different root traits such as rooting depth (RD), root dry mass (RM), total root length (RL), root diameter (Rdia) and root surface areas (RSA1 for coarse roots and RSA2 for fine roots) under controlled conditions in a semi-hydroponic system. We detected 14 QTL for eight root traits on nine wheat chromosomes; we discovered three QTL each for RD and RSA1, two QTL each for RM and RSA2, and one QTL each for RL, Rdia, specific root length and nodal root number per plant. The detected QTL were concentrated on chromosome groups 5, 6 and 7. The QTL for shallow RD (Q.rd.uwa.7BL: Xbarc50) and high RM (Q.rm.uwa.6AS: Xgwm334) were validated in two independent F₂ populations of Synthetic W7984 × Chara and Opata M85 × Cascade, respectively. Genotypes containing negative alleles for Q.rd.uwa.7BL had 52% shallower RD than other Synthetic W7984 × Chara population lines. Genotypes with the positive alleles for Q.rm.uwa.6AS had 31.58% higher RM than other Opata M85 × Cascade population lines. Further, we identified 21 putative candidate genes for RD (Q.rd.uwa.7BL) and 13 for RM (Q.rm.uwa.6AS); TraesCS6A01G020400, TraesCS6A01G024400 and TraesCS6A01G021000 identified from Q.rm.uwa.6AS, and TraesCS7B01G404000, TraesCS7B01G254900 and TraesCS7B01G446200 identified from Q.rd.uwa.7BL encoded important proteins for root traits. We found germin-like protein encoding genes in both Q.rd.uwa.7BL and Q.rm.uwa.6AS regions. These genes may play an important role in RM and RD improvement. The identified QTL, especially the validated QTL and putative candidate genes are valuable genetic resources for future root trait improvement in wheat.

Positional cloning and characterization reveal the role of a miRNA precursor gene ZmLRT in the regulation of lateral root number and drought tolerance in maize

Lateral roots play essential roles in drought tolerance in maize (Zea mays L.). However, the genetic basis for the variation in the number of lateral roots in maize remains elusive. Here, we identified a major quantitative trait locus (QTL), qLRT5-1, controlling lateral root number using a recombinant inbred population from a cross between the maize lines Zong3 (with many lateral roots) and 87-1 (with few lateral roots). Fine-mapping and functional analysis determined that the candidate gene for qLRT5-1, ZmLRT, expresses the primary transcript for the microRNA miR166a. ZmLRT was highly expressed in root tips and lateral root primordia, and knockout and overexpression of ZmLRT increased and decreased lateral root number, respectively. Compared with 87-1, the ZmLRT gene model of Zong3 lacked the second and third exons and contained a 14 bp deletion at the junction between the first exon and intron, which altered the splicing site. In addition, ZmLRT expression was significantly lower in Zong3 than in 87-1, which might be attributed to the insertions of a transposon and over large DNA fragments in the Zong3 ZmLRT promoter region. These mutations decreased the abundance of mature miR166a in Zong3, resulting in increased lateral roots at the seedling stage. Furthermore, miR166a post-transcriptionally repressed five development-related class-III homeodomain-leucine zipper genes. Moreover, knockout of ZmLRT enhanced drought tolerance of maize seedlings. Our study furthers our understanding of the genetic basis of lateral root number variation in maize and highlights ZmLRT as a target for improving drought tolerance in maize.

Effects of Co-Inoculating Saccharomyces spp. with Bradyrhizobium japonicum on Atmospheric Nitrogen Fixation in Soybeans (Glycine max (L.))

Crop production encounters challenges due to the dearth of nitrogen (N) and phosphorus (P), while excessive chemical fertilizer use causes environmental hazards. The use of N-fixing microbes and P-solubilizing microbes (PSMs) can be a sustainable strategy to overcome these problems. Here, we conducted a greenhouse pot experiment following a completely randomized blocked design to elucidate the influence of co-inoculating N-fixing bacteria (Bradyrhizobium japonicum) and PSMs (Saccharomyces cerevisiae and Saccharomyces exiguus) on atmospheric N₂-fixation, growth, and yield. The results indicate a significant influence of interaction on Indole-3-acetic acid production, P solubilization, seedling germination, and growth. It was also found that atmospheric N₂-fixation, nodule number per plant, nodule dry weight, straw, and root dry weight per plant at different growth stages were significantly increased under dual inoculation treatments relative to single inoculation or no inoculation treatment. Increased seed yield and N and P accumulation were also noticed under co-inoculation treatments. Soil available N was highest under sole bacterial inoculation and lowest under the control treatment, while soil available P was highest under co-inoculation treatments and lowest under the control treatment. We demonstrated that the co-inoculation of N-fixing bacteria and PSMs enhances P bioavailability and atmospheric N₂-fixation in soybeans leading to improved soil fertility, raising crop yields, and promoting sustainable agriculture.

A Potential Application of Pseudomonas psychrotolerans IALR632 for Lettuce Growth Promotion in Hydroponics

Controlled environment agriculture hydroponic systems grow plants year-round without restriction from outside environmental conditions. In order to further improve crop yield, plant growth-promoting bacteria were tested on hydroponically grown lettuce (Lactuca sativa) plants. From our bacterial endophyte library, we found one bacterium, Pseudomonas psychrotolerans IALR632, that is promising in promoting lettuce growth in multiple hydroponic systems. When Green Oakleaf lettuce seeds were inoculated with IALR632 during germination, IALR632 significantly increased lateral root development by 164%. When germinated seedlings were inoculated with IALR632 and then transplanted to different hydroponic systems, shoot and root fresh weights of Green Oakleaf increased by 55.3% and 17.2% in a nutrient film technique (NFT) system in the greenhouse, 13.5% and 13.8% in an indoor vertical NFT system, and 15.3% and 13.6% in a deep water cultivation (DWC) system, respectively. IALR632 also significantly increased shoot fresh weights of Rex by 33.9%, Red Oakleaf by 21.0%, Red Sweet Crisp by 15.2%, and Nancy by 29.9%, as well as Red Rosie by 8.6% (no significant difference). Inoculation of IALR632-GFP and subsequent analysis by confocal microscopy demonstrated the endophytic nature and translocation from roots to shoots. The results indicate that P. psychrotolerans IALR632 has a potential application in hydroponically grown lettuce plants.

Genetic analysis of grapevine root system architecture and loci associated gene networks

Own-rooted grapevines and grapevine rootstocks are vegetatively propagated from cuttings and have an adventitious root system. Unraveling the genetic underpinnings of the adventitious root system architecture (RSA) is important for improving own-rooted and grafted grapevine sustainability for a changing climate. Grapevine RSA genetic analysis was conducted in an Vitis sp. 'VRS-F2' population. Nine root morphology, three total root system morphology, and two biomass traits that contribute to root anchorage and water and nutrient uptake were phenotyped. Quantitative trait loci (QTL) analysis was performed using a high density integrated GBS and rhAmpSeq genetic map. Thirty-one QTL were detected for eleven of the RSA traits (surface area, root volume, total root length, fresh weight, number of tips, forks or links, longest root and average root diameter, link length, and link surface area) revealing many small effects. Several QTL were colocated on chromosomes 1, 9, 13, 18, and 19. QTL with identical peak positions on chromosomes 1 or 13 were enriched for AP2-EREBP, AS2, C2C2-CO, HMG, and MYB transcription factors, and QTL on chromosomes 9 or 13 were enriched for the ALFIN-LIKE transcription factor and regulation of autophagy pathways. QTL modeling for individual root traits identified eight models explaining 13.2 to 31.8% of the phenotypic variation. 'Seyval blanc' was the grandparent contributing to the allele models that included a greater surface area, total root length, and branching (number of forks and links) traits promoting a greater root density. In contrast, V. riparia 'Manitoba 37' contributed the allele for greater average branch length (link length) and diameter, promoting a less dense elongated root system with thicker roots. LATERAL ORGAN BOUNDARY DOMAIN (LBD or AS2/LOB) and the PROTODERMAL FACTOR (PFD2 and ANL2) were identified as important candidate genes in the enriched pathways underlying the hotspots for grapevine adventitious RSA. The combined QTL hotspot and trait modeling identified transcription factors, cell cycle and circadian rhythm genes with a known role in root cell and epidermal layer differentiation, lateral root development and cortex thickness. These genes are candidates for tailoring grapevine root system texture, density and length in breeding programs.

Plant-soil-microbes: A tripartite interaction for nutrient acquisition and better plant growth for sustainable agricultural practices

Plants can achieve their proper growth and development with the help of microorganisms associated with them. Plant-associated microbes convert the unavailable nutrients to available form and make them useful for plants. Besides nutrient acquisition, soil microbes also inhibit the pathogens that cause harm to plant growth and induces defense response. Due to the beneficial activities of soil nutrient-microbe-plant interactions, it is necessary to study more on this topic and develop microbial inoculant technology in the agricultural field for better crop improvement. The soil microbes can be engineered, and plant growth-promoting rhizobacteria (PGPR) and plant growth-promoting bacteria (PGPB) technology can be developed as well, as its application can be improved for utilization as biofertilizer, biopesticides, etc., instead of using harmful chemical biofertilizers. Moreover, plant growth-promoting microbe inoculants can enhance crop productivity. Although, scientists have discussed several tools and techniques by omics and gene editing approaches for crop improvement to avoid biotic and abiotic stress and make the plant healthier and more nutritive. However, beneficial soil microbes that help plants with the nutrient acquisition, development, and stress resistance were ignored, and farmers started utilizing chemical fertilizers. Thus, this review attempts to summarize the interaction system of plant microbes, the role of beneficiary soil microbes in the rhizosphere zone, and their role in plant health promotion, particularly in the nutrition acquisition of the plant. The review will also provide a better understanding of soil microbes that can be exploited as biofertilizers and plant growth promoters in the field to create environmentally friendly, sustainable agriculture systems.

Guvermectin, a novel plant growth regulator, can promote the growth and high temperature tolerance of maize

Guvermectin is a recently discovered microbial N9-glucoside cytokinin compound extracted from Streptomyces sanjiangensis NEAU6. Although some research has reported that N9-glucoside cytokinin compounds do not have the activity of cytokinin, it has been noted that guvermectin can promote growth and antifungal activity in Arabidopsis. Maize is an important food crop in the world and exploring the effect of guvermectin on this crop could help its cultivation in regions with adverse environmental conditions such as a high temperature. Here, we investigated the effects of guvermectin seed soaking treatment on the growth of maize at the seedlings stage and its yield attributes with different temperature stresses. The maize (cv. Zhengdan 958) with guvermectin seed soaking treatment were in two systems: paper roll culture and field conditions. Guvermectin seed soaking treated plants had increased plant height, root length, and mesocotyl length at the seedlings stage, and spike weight at maturity in the field. But only root length was increased at the paper roll culture by guvermectin seed soaking treatment. Guvermectin seed soaking treatment reduced the adverse effects on maize seedling when grow at a high temperature. Further experiments showed that, in high temperature conditions, guvermectin treatment promoted the accumulation of heat shock protein (HSP) 17.0, HSP 17.4 and HSP 17.9 in maize roots. Comparative transcriptomic profiling showed there were 33 common differentially expressed genes (DEGs) in guvermectin treated plants under high temperature and room temperature conditions. The DEGs suggested that guvermectin treatment led to the differential modulation of several transcripts mainly related with plant defense, stress response, and terpenoid biosynthesis. Taken together, these results suggested that the guvermectin treatment promoted the growth and tolerance of high temperature stresses, possibly by activation of related pathways. These results show that guvermectin is a novel plant growth regulator and could be developed as an application to maize seeds to promote growth in high temperature environments.

Negative Interactions Balance Growth and Defense in Plants Confronted with Herbivores or Pathogens

Plants have evolved a series of defensive mechanisms against pathogens and herbivores, but the defense response always leads to decreases in growth or reproduction, which has serious implications for agricultural production. Growth and defense are negatively regulated not only through metabolic consumption but also through the antagonism of different phytohormones, such as jasmonic acid (JA) and salicylic acid (SA). Meanwhile, plants can limit the expression of defensive metabolites to reduce the costs of defense by producing constitutive defenses such as glandular trichomes or latex and accumulating specific metabolites, determining the activation of plant defense or the maintenance of plant growth. Interestingly, plant defense pathways might be prepared in advance which may be transmitted to descendants. Plants can also use external organisms to protect themselves, thus minimizing the costs of defense. In addition, plant relatives exhibit cooperation to deal with pathogens and herbivores, which is also a way to regulate growth and defense.

Transcriptomic analysis and physiological characteristics of exogenous naphthylacetic acid application to regulate the healing process of oriental melon grafted onto squash

The plant graft healing process is an intricate development influenced by numerous endogenous and environmental factors. This process involves the histological changes, physiological and biochemical reactions, signal transduction, and hormone exchanges in the grafting junction. Studies have shown that applying exogenous plant growth regulators can effectively promote the graft healing process and improve the quality of grafted plantlets. However, the physiological and molecular mechanism of graft healing formation remains unclear. In our present study, transcriptome changes in the melon and cucurbita genomes were analyzed between control and NAA treatment, and we provided the first view of complex networks to regulate graft healing under exogenous NAA application. The results showed that the exogenous NAA application could accelerate the graft healing process of oriental melon scion grafted onto squash rootstock through histological observation, increase the SOD, POD, PAL, and PPO activities during graft union development and enhance the contents of IAA, GA₃, and ZR except for the IL stage. The DEGs were identified in the plant hormone signal-transduction, phenylpropanoid biosynthesis, and phenylalanine metabolism through transcriptome analysis of CK vs. NAA at the IL, CA, and VB stage by KEGG pathway enrichment analysis. Moreover, the exogenous NAA application significantly promoted the expression of genes involved in the hormone signal-transduction pathway, ROS scavenging system, and vascular bundle formation.

Fungal endophytes of Brassicaceae: Molecular interactions and crop benefits

Brassicaceae family includes an important group of plants of great scientific interest, e.g., the model plant Arabidopsis thaliana, and of economic interest, such as crops of the genus Brassica (Brassica oleracea, Brassica napus, Brassica rapa, etc.). This group of plants is characterized by the synthesis and accumulation in their tissues of secondary metabolites called glucosinolates (GSLs), sulfur-containing compounds mainly involved in plant defense against pathogens and pests. Brassicaceae plants are among the 30% of plant species that cannot establish optimal associations with mycorrhizal hosts (together with other plant families such as Proteaceae, Chenopodiaceae, and Caryophyllaceae), and GSLs could be involved in this evolutionary process of non-interaction. However, this group of plants can establish beneficial interactions with endophytic fungi, which requires a reduction of defensive responses by the host plant and/or an evasion, tolerance, or suppression of plant defenses by the fungus. Although much remains to be known about the mechanisms involved in the Brassicaceae-endophyte fungal interaction, several cases have been described, in which the fungi need to interfere with the GSL synthesis and hydrolysis in the host plant, or even directly degrade GSLs before they are hydrolyzed to antifungal isothiocyanates. Once the Brassicaceae-endophyte fungus symbiosis is formed, the host plant can obtain important benefits from an agricultural point of view, such as plant growth promotion and increase in yield and quality, increased tolerance to abiotic stresses, and direct and indirect control of plant pests and diseases. This review compiles the studies on the interaction between endophytic fungi and Brassicaceae plants, discussing the mechanisms involved in the success of the symbiosis, together with the benefits obtained by these plants. Due to their unique characteristics, the family Brassicaceae can be seen as a fruitful source of novel beneficial endophytes with applications to crops, as well as to generate new models of study that allow us to better understand the interactions of these amazing fungi with plants.

CRISPR-Based Genome Editing for Nutrient Enrichment in Crops: A Promising Approach Toward Global Food Security

The global malnutrition burden imparts long-term developmental, economic, social, and medical consequences to individuals, communities, and countries. The current developments in biotechnology have infused biofortification in several food crops to fight malnutrition. However, these methods are not sustainable and suffer from several limitations, which are being solved by the CRISPR-Cas-based system of genome editing. The pin-pointed approach of CRISPR-based genome editing has made it a top-notch method due to targeted gene editing, thus making it free from ethical issues faced by transgenic crops. The CRISPR-Cas genome-editing tool has been extensively used in crop improvement programs due to its more straightforward design, low methodology cost, high efficiency, good reproducibility, and quick cycle. The system is now being utilized in the biofortification of cereal crops such as rice, wheat, barley, and maize, including vegetable crops such as potato and tomato. The CRISPR-Cas-based crop genome editing has been utilized in imparting/producing qualitative enhancement in aroma, shelf life, sweetness, and quantitative improvement in starch, protein, gamma-aminobutyric acid (GABA), oleic acid, anthocyanin, phytic acid, gluten, and steroidal glycoalkaloid contents. Some varieties have even been modified to become disease and stress-resistant. Thus, the present review critically discusses CRISPR-Cas genome editing-based biofortification of crops for imparting nutraceutical properties.

The Hierarchy of Protoxylem Groupings in Primary Root and Their Plasticity to Nitrogen Addition in Three Tree Species

Protoxylem grouping (PG), a classification based on the number of protoxylem poles, is a crucial indicator related to other functional traits in fine roots, affecting growth and survival of individual root. However, within root system, less is known about the arrangement of PG. Moreover, the responses of PG to fertilization are still unclear. Here, we selected three common hardwood species in Northeast China, Juglans mandshurica, Fraxinus mandshurica, and Phellodendron amurense, conducted root pruning and nutrient addition. In this study, we analyzed the PG, morphology, and other anatomy traits of newly formed root branches. The results showed all root length, diameter, and stele, as well as hydraulic conductivity, were significantly positive related to the PG number, and the PG number generally decreased with ascending root developmental order; these patterns were independent of species and fertilization. Additionally, we also found the plasticity of PGs to environmental changes, in terms of the increased frequency of high PG roots after fertilization, significantly in J. mandshurica and F. mandshurica. Therefore, the heterogeneity, hierarchy, and plasticity of individual roots within root system may be widespread in woody plants, which is of great significance to deepen our understanding in root growth and development, as well as the belowground ecological process.

From Soil Amendments to Controlling Autophagy: Supporting Plant Metabolism under Conditions of Water Shortage and Salinity

Crop resistance to environmental stress is a major issue. The globally increasing land degradation and desertification enhance the demand on management practices to balance both food and environmental objectives, including strategies that tighten nutrient cycles and maintain yields. Agriculture needs to provide, among other things, future additional ecosystem services, such as water quantity and quality, runoff control, soil fertility maintenance, carbon storage, climate regulation, and biodiversity. Numerous research projects have focused on the food–soil–climate nexus, and results were summarized in several reviews during the last decades. Based on this impressive piece of information, we have selected only a few aspects with the intention of studying plant–soil interactions and methods for optimization. In the short term, the use of soil amendments is currently attracting great interest to cover the current demand in agriculture. We will discuss the impact of biochar at water shortage, and plant growth promoting bacteria (PGPB) at improving nutrient supply to plants. In this review, our focus is on the interplay of both soil amendments on primary reactions of photosynthesis, plant growth conditions, and signaling during adaptation to environmental stress. Moreover, we aim at providing a general overview of how dehydration and salinity affect signaling in cells. With the use of the example of abscisic acid (ABA) and ethylene, we discuss the effects that can be observed when biochar and PGPB are used in the presence of stress. The stress response of plants is a multifactorial trait. Nevertheless, we will show that plants follow a general concept to adapt to unfavorable environmental conditions in the short and long term. However, plant species differ in the upper and lower regulatory limits of gene expression. Therefore, the presented data may help in the identification of traits for future breeding of stress-resistant crops. One target for breeding could be the removal and efficient recycling of damaged as well as needless compounds and structures. Furthermore, in this context, we will show that autophagy can be a useful goal of breeding measures, since the recycling of building blocks helps the cells to overcome a period of imbalanced substrate supply during stress adjustment.