Plant Biotechnology最新文献

Alkaloids represent one of the largest classes of plant specialized metabolites, characterized by diverse chemical structures and activities. Known for their bioactive properties, these metabolites have primarily been described in the context of aboveground defense against pathogens, insects, and herbivores. Beyond these defensive functions, recent studies have revealed that alkaloids also mediate interactions between plants and their associated root microbiota. These interkingdom metabolic interactions improves plant fitness, particularly under changing environmental conditions. This review highlights the metabolism and roles of alkaloids in the rhizosphere, a critical hotspot for interactions between plants and soil microbes. We also explore key questions that expand our understanding of the role of plant specialized metabolites, extending beyond alkaloids, in plant-microbiota interactions and their broader implications for plant fitness.

Microbial bioinoculants should play important roles to achieve sustainable phosphorus (P) management in agriculture. Colletotrichum tofieldiae (Ct), a fungal endophyte, is a promising material that supports phosphorus acquisition in Arabidopsis under low phosphorus (P) conditions and promotes maize and tomato growth in a greenhouse. However, its effects on leafy vegetables such as komatsuna, particularly those with a range of P availability in the soil, remain largely unclear. This study evaluated the impact of Ct inoculation on komatsuna growth, P uptake, rhizosphere soil and plant microbiological properties in sterilized and non-sterilized farm soils in Japan. The Ct mycelium was incubated in a mixture of rice bran, wheat bran, and wood chips for two weeks, and then applied to the soils at 0%, 1%, and 5% mass ratios (Ct0, Ct1, Ct5). Ct0 was the sterilized medium applied at a 5% mass ratio. Non-sterilized and sterilized soils received 20 and 80 mg P kg^-1 as low and high P treatments, respectively. Ct significantly increased plant biomass in a manner dependent on the initial inoculation dose in Low P- and High P-amended soils, although Ct-mediated plant growth promotion was more prominent in the low P-supplemented soils. Furthermore, Ct inoculation was found to increase microbial activity such as P solubilization, in rhizosphere soil and/or roots under both P conditions. This study is the first to demonstrate the positive influence of Ct on Brassicaceae growth in not only P-deficient but also P-supplemented soils, confirming its potential to improve plant development under P-deficient and P-supplemented soil conditions.

Bacillus pumilus TUAT1, a gram-positive and spore-forming plant growth-promoting rhizobacterium, has been utilized as a biofertilizer due to its robust ability as spores to withstand environmental stresses and ensure long-term viability. This study investigated the mechanisms underlying the plant growth-promoting effects of spores and vegetative cells. Elemental analyses revealed that endospores are enriched in carbon, calcium, and manganese, which contribute to their protective properties, while vegetative cells are richer in nitrogen and phosphorus. Notably, both viable and dead spores and vegetative cells promoted the growth of Setaria viridis in natural soil. Microbial community analysis showed that bacterial alpha diversity was not changed across treatments, whereas beta diversity varied significantly, forming distinctly separated groups influenced by planting and inoculation. Fungal community analysis exhibited increased alpha diversity due to Setaria planting but no significant effects from bacterial treatments. Enrichment of Bdellovibrio spp., Bacteriovorax spp., and Pseudomonas spp. in soil inoculated with viable and dead vegetative cells and spores highlighted the capability of indirect mechanisms through microbial interactions rather than direct nutrient supply from bacterial residues. We believe that bacterial inoculants, including dead cells, modulate soil microbial communities to enhance plant growth, emphasizing their potential in sustainable agriculture.

Hairy root transformation mediated by Rhizobium rhizogenes is a widely used tool for molecular analysis and root material for secondary metabolite production. However, this method is time-intensive, technically demanding, and exhibits low transformation efficiency. To address these limitations, we developed a rapid and efficient hairy root transformation system for legume crops, optimizing protocols with the soybean (Glycine max L. Merrill) cultivar Fukuyutaka. Sterilizing seeds with vapor of 5% sodium hypochlorite and germinating them in a double-tier container resulted in over 90% healthy, straight seedlings ideal for transformation, with 3- to 5-day-old seedlings showing the highest transformation rates. Exposing the plant shoot during co-cultivation by covering only the injection area, combined with low nitrogen levels in the hydroponic solution, significantly enhanced hairy root production, yielding up to 16 transgenic hairy roots per plant. Additionally, low nitrogen concentrations were crucial for promoting nodule formation in transgenic hairy roots. These optimized conditions were validated across 12 soybean, 1 cowpea, and 1 mungbean cultivars. The protocol's effectiveness was confirmed through the induction of symbiotic gene expression of GmEnod40a and GmErn1b using a promoter β-glucuronidase (GUS) reporter system in transgenic hairy roots. Expression of these genes was detected in both premature and mature nodules, while GmErn1b expression was also observed in epidermal cells during early nodulation. This optimized hairy root transformation protocol, requiring under 22 days from seed sterilization to transgenic root induction and 61 days to expression analysis, offers a promising approach for efficient gene function studies in legume crops.

The Lysinibacillus xylanilyticus strain GIC41 has been previously reported to promote spinach growth. This study evaluated GIC41's potential as a biostimulant by assessing its ability to mitigate Pythium root rot and enhance plant growth across various cultivation systems. In a pot experiment, GIC41 application to potting soil reduced the disease severity index (DSI) by approximately 52% in spinach seedlings 15 days post-pathogen inoculation (dpi). Similarly, introducing GIC41 into hydroponic nutrient solutions decreased the DSI in tomato seedlings from 61% to 15% at 14 dpi. Reisolation experiments and quantitative real-time PCR analysis confirmed that GIC41 significantly suppressed root colonization by Pythium aphanidermatum in both spinach and tomato seedlings. Microscopic analysis showed that GIC41 treatment inhibited pathogen mycelial colonization and caused morphological abnormalities in about 93% of encysted zoospores on the tomato rhizoplane. Although GIC41 exhibited no direct anti-oomycete activity in dual culture, it produced protease. Notably, GIC41 treatment significantly improved plant growth, increasing tomato shoot dry weight and stem diameter by 47% and 43%, respectively. These findings suggest that GIC41 is a promising biostimulant, offering dual benefits of disease mitigation and growth promotion across different crops and cultivation systems.

Nitrogen fixation in soybean occurs as a result of symbiosis between the plant and rhizobia in the nodules. This process allows both the plant and the symbiont to acquire vital nutrition. To fully understand the symbiosis, many researchers have attempted to attain a deeper interpretation of the biomolecular behavior or enhance the nitrogen fixation activity of bacteroids. However, most studies have focused on forward and reverse genetics approaches to evaluate the contribution of a particular gene/enzyme in nitrogen fixation. Few studies have observed the bacteroids' overall biomolecular behavior in the nodules. Thus, we grew soybean plants and recorded acetylene reduction assay (ARA) results at several growth stages. Simultaneously, we analyzed the biomolecular compounds in the bacteroids in the nodules at the single-cell level by Raman microspectroscopy. Random forest regression, a machine learning method, was applied to discover the biomolecular contribution to the ARA, as it predicted ARA results with high accuracy. Polyhydroxybutyrate (PHB) biopolymer significantly contributed to predicting ARA results, suggesting its potential relevance in symbiotic nitrogen fixation in soybean. Further studies related to PHB behavior will lead to a deeper understanding of symbiotic nitrogen fixation and may help achieve better control of this process to increase crop yields.

Plant-specialized metabolites (PSMs) act as candidate drivers of rhizosphere microbiome assembly by recruiting specific microbial taxa. The resulting PSM-microbe interactions influence the host-plant fitness and population dynamics, ultimately impacting the aboveground biodiversity. Although saponins are widely distributed PSMs in the angiosperms, their dynamics and impact on soil microbiomes in a natural ecosystem remain unclear. Here, we investigated the ecological role of a triterpenoid saponin, ardisiacrispin, synthesized by the shade-tolerant shrub Ardisia crenata (Primulaceae), in a forest ecosystem. First, we quantified the saponin concentrations in both the roots and rhizosphere soils of A. crenata at two different developmental stages (i.e., seedling and adult). Next, we assessed how saponin treatment alters the microbial communities in forest soil. Finally, we integrated 16S rRNA and the internal transcribed spacer region sequencing data from the field-collected A. crenata rhizosphere with the results from in vitro saponin-treatment experiments to determine whether saponins selectively enrich or deplete specific microbial taxa. We found that the rhizosphere saponin content primarily varies with the developmental stages of A. crenata, with higher saponin concentrations in adults than in seedlings. The saponin-treatment experiments revealed that ardisiacrispins modify the soil microbial diversity and community structure in accordance with their concentration. Moreover, several microbial taxa were consistently enriched or depleted in the saponin-treated soil, which mirrors the shifts observed from seedling to adult rhizospheres. Thus, ardisiacrispin can mediate rhizosphere microbial community assembly in a natural ecosystem. Our findings highlight the importance of the developmental stage-specific accumulation of saponins in the rhizosphere for plant-microbe interactions.

Arbuscular mycorrhizal fungi (AMF) are representative symbiotic partners of plants, and trade nutrients with them. This symbiotic association confers plants with the agronomically beneficial traits such as plant growth promotion and stress tolerance. Arbuscular mycorrhizae (AM) are divided into two morphotypes, the Arum-type and the Paris-type, based on fungal structures within the host plant cells. Although the phylogeny of host plants typically determines the AM morphotype, the AMF, Rhizophagus irregularis and Gigaspora margarita, can form Arum-type AM and Paris-type AM, respectively, in tomato (Solanum lycopersicum). In this study, the traits resulting from the AM symbiosis and root transcriptomes between Lotus japonicus and tomato inoculated with these two phylogenetically distal AMF were compared. In L. japonicus, Arum-type AMs formed when colonized by both AMF, as expected. Shoot growth in both plants was significantly promoted when inoculated by these AMF, although the impact of G. margarita was greater than that by R. irregularis colonization. A transcriptome analysis of both plants inoculated by the two AMF strongly suggested changes in the expression levels of genes associated with defense response. AMF inoculation induced resistance against Fusarium diseases in both plants, but the level of disease resistance in Rhizophagus-colonized plants was higher than in Gigaspora-colonized plants. Thus, the colonized AMF identity, and not the AM morphotype, determines the level of AM-induced traits, plant growth promotion and disease resistance. Negative relationships between these two traits would exist as a growth-defense tradeoff to fine-tune the balance in response to limited resources, and to optimize fitness.

The rhizosphere, a narrow zone of soil directly influenced by plant roots, serves as a highly dynamic interface where biochemical and ecological interactions converge to sustain plant growth. This critical region facilitates intricate chemical exchanges among plants, soil, and microorganisms, thereby shaping nutrient availability, microbial community structures, and plant defense mechanisms. While root exudates that are mostly non-volatile have long been the primal interest as ecologically crucial chemicals in the rhizosphere, recent advancements in analytical methodologies have illuminated the roles of volatile organic compounds produced by soil microorganisms (mVOCs) and plant roots (rVOCs) as intricate mediators that regulate plant physiology and microbial community dynamics. mVOCs exhibit diverse functions, including stimulating root development, enhancing systemic resistance, and suppressing pathogen activity, thereby contributing to plant health. Conversely, rVOCs support soil microorganisms in establishing ecological niches in association with plants. mVOCs and rVOCs, together with root exudates, create feedback loops that drive ecological processes in the rhizosphere and enable plants to adapt to environmental challenges. This review synthesizes current understanding in the composition, molecular mechanisms, ecological relevance, and potential applications of mVOCs and rVOCs, with a particular emphasis on their interplay with non-volatile root exudates. The integration of these insights offers a molecular foundation for advancing sustainable agricultural practices and tackling pressing global challenges, such as ensuring food security and mitigating environmental degradation exacerbated by climate change.

Plants emit a variety of volatile organic compounds (VOCs), including C1-compounds such as methane and methanol, which are major components of plant-derived VOCs. A group of microorganisms called methylotrophs or C1-microorganisms utilize these C1-compounds as a single source of carbon and energy and contribute to driving the global carbon cycle between two major greenhouse gases, CO₂ and methane. C1-microorganisms inhabit the surface of the above-ground part of plants (phyllosphere), and utilize methane and methanol before they are released into the atmosphere. Among C1-microorganisms, Methylobacterium spp., the representative of methanol-utilizing bacteria and dominant colonizers in the phyllosphere, are known to exhibit positive effects on plants. Thus, the interactions between C1-microorganisms and plants affect not only the consumption of C1-compounds generated by plants but also CO₂ fixation by plants. This review describes our recent understanding of the ecology and physiology of C1-microorganisms living in the phyllosphere and their application in plant biotechnology. Specifically, the ways in which these phyllosphere C1-microorganisms can be used for mitigating methane emissions as well as their application as biostimulants for increasing crop yield are discussed.