The access of rhizobia to legume host is a prerequisite for nodulation. Rhizobia are poorly motile in soil, while filamentous fungi are known to grow extensively across soil pores. Since root ...exudates-driven bacterial chemotaxis cannot explain rhizobial long-distance dispersal, mycelia could constitute ideal dispersal networks to help rhizobial enrichment in the legume rhizosphere from bulk soil. Thus, we hypothesized that mycelia networks act as vectors that enable contact between rhizobia and legume and influence subsequent nodulation. By developing a soil microcosm system, we found that a facultatively biotrophic fungus, Phomopsis liquidambaris, helps rhizobial migration from bulk soil to the peanut (Arachis hypogaea) rhizosphere and, hence, triggers peanut-rhizobium nodulation but not seen in the absence of mycelia. Assays of dispersal modes suggested that cell proliferation and motility mediated rhizobial dispersal along mycelia, and fungal exudates might contribute to this process. Furthermore, transcriptomic analysis indicated that genes associated with the cell division, chemosensory system, flagellum biosynthesis, and motility were regulated by Ph. liquidambaris, thus accounting for the detected rhizobial dispersal along hyphae. Our results indicate that rhizobia use mycelia as dispersal networks that migrate to legume rhizosphere and trigger nodulation. This work highlights the importance of mycelial network-based bacterial dispersal in legume-rhizobium symbiosis.
The role of flowering in root‐fungal symbiosis is not well understood. Because flowering and fungal symbionts are supported by carbohydrates, we hypothesized that flowering modulates root‐beneficial ...fungal associations through alterations in carbohydrate metabolism and transport. We monitored fungal colonization and soluble sugars in the roots of Arabidopsis thaliana following inoculation with a mutualistic fungus Phomopsis liquidambari across different plant developmental stages. Jasmonate signalling of wild‐type plants, sugar transport, and root invertase of wild‐type and jasmonate‐insensitive plants were exploited to assess whether and how jasmonate‐dependent sugar dynamics are involved in flowering‐mediated fungal colonization alterations. We found that flowering restricts root‐fungal colonization and activates root jasmonate signalling upon fungal inoculation. Jasmonates reduce the constitutive and fungus‐induced accumulation of root glucose and fructose at the flowering stage. Further experiments with sugar transport and metabolism mutant lines revealed that root glucose and fructose positively influence fungal colonization. Diurnal, jasmonate‐dependent inhibitions of sugar transport and soluble invertase activity were identified as likely mechanisms for flowering‐mediated root sugar depletion upon fungal inoculation. Collectively, our results reveal that flowering drives root‐fungus cooperation loss, which is related to jasmonate‐dependent root soluble sugar depletion. Limiting the spread of root‐fungal colonization may direct more resources to flower development.
In the present study, we determined whether and how plant flowering affects root‐fungal mutualism. Our results revealed a novel metabolic network in which plant flowering‐mediated root fungal colonization is related to jasmonate‐dependent root glucose and fructose deprivation. The reductions of root glucose and fructose were probably due to the inhibitions of phloem sugar transport and root soluble invertase activity. Our results highlight importance of plant flowering in root microbiota composition.
Aims
This study evaluated the control effect of the endophytic fungus Phomopsis liquidambaris B3 against rice bakanae disease (RBD) caused by Fusarium proliferatum and the disease control result of ...different inoculation times of beneficial micro‐organisms.
Methods and Results
Rice seedlings preinoculated, coinoculated and noninoculated with B3 were exposed to F. proliferatum stress and grown under controlled conditions. Greenhouse experimental results showed that rice preinoculation with B3 significantly reduced rice bakanae disease by 21.45%, inhibited the colonization of F. proliferatum, increased defence‐related enzyme activities, upregulated the expression of defence genes and promoted plant photosynthesis. However, bakanae disease in rice coinoculation with B3 increased by 11.45%, resulted in excessive reactive oxygen species (ROS) bursts and plant cell death.
Conclusions
Preinoculation with the endophytic fungus P. liquidambaris B3 significantly reduced rice bakanae disease by triggering the SA‐dependent defence pathways of plants, and promoted plant growth. However, coinoculatiton with P. liquidambaris B3 activated excessive defence responses, resulting in plants cell death and aggravation of bakanae disease.
Significance and Impact of the Study
This study indicated that P. liquidambaris B3 was an effective method for agricultural control against rice bakanae disease caused by F. proliferatum, and provides an experimental basis for the development of sustainable endophytic fungal resources to effectively control plant diseases caused by pathogenic fungi, and suggests that precise application of beneficial micro‐organisms may be become a key factor in farmland crop disease management.
Filamentous fungi can produce many valuable secondary metabolites; among these fungi, endophytic fungi play an ecological role in mutualistic symbiosis with plants, including promoting plant growth, ...disease resistance, and stress resistance. However, the biosynthesis of most secondary metabolites remains unclear, and knowledge of the interaction mechanisms between endophytes and plants is still limited, especially for some novel fungi, due to the lack of genetic manipulation tools for novel species. Herein, we review the newly discovered strategies of gene disruption, such as the CRISPR-Cas9 system, the site-specific recombination
Cre/loxP
system, and the I-
SceI
endonuclease-mediated system in filamentous fungi. Gene expression systems contain using integration of target genes into the genome, host-dependent expression cassette construction depending on the host, a host-independent, universal expression system independent of the host, and reporter-guided gene expression for filamentous fungi. Furthermore, the Newly CRISPRi, CRISPRa, and the selection markers were also discussed for gene disruption and gene expression were also discussed. These studies lay the foundation for the biosynthesis of secondary metabolites in these organisms and aid in understanding the ecological function of filamentous fungi.
The bacterial endophyte Pseudomonas fluorescens ALEB7B significantly enhances photosynthate accumulations in Atractylodes lancea. These carbohydrates are preferentially used by the host plant to ...synthesize secondary metabolites, rather than to increase plant biomass accumulation. Mechanisms underlying the allocation of endophyte–increased carbohydrate in different plant metabolic processes are largely unknown. We have studied how P. fluorescens ALEB7B enhances photosynthate accumulation and how bacterial elicitors regulate metabolic flux and increase medicinal sesquiterpenoid formation in A. lancea using the sterile tissue culture plantlets. P. fluorescens ALEB7B enhances plant photosynthate accumulation by synthesizing and secreting indole–3–acetic acid, which has been demonstrated using high–performance liquid chromatography analysis. The increased endogenous indole–3–acetic acid promotes plant root development and then assimilation. Increased carbohydrates provide the material basis for the formations of terpenoid hydrocarbon scaffolds, which has been proved using gas chromatography analysis. Further, protein and polysaccharide elicitors secreted by P. fluorescens ALEB7B have been separated and purified from the bacterial fermentation broth, which have been applied to A. lancea plantlets. Both elicitors can stimulate the conversions of terpenoid hydrocarbon scaffolds to oxygenous sesquiterpenoids, the active medicinal ingredients in A. lancea, by triggering the oxidative burst in planta. Moreover, this study separates an ABC transporter substrate–binding protein from protein elicitors secreted by P. fluorescens ALEB7B with an ÄKTA Prime Plus Purifier System and firstly shows that this protein is essential to induce oxygenous sesquiterpenoid accumulation in A. lancea. This study provides new perspectives for mechanisms of medicinal oxygenous terpenoid synthesis, which has important reference values to the cultivation of medicinal plants that have terpenoids as their active ingredients, such as Artemisia annua and Taxus chinensis.
•Pseudomonas fluorescens enhances carbohydrate accumulation in Atractylodes lancea.•P. fluoredscens promotes plant primary metabolism by secreting indole–3–acetic acid.•A. lancea prefers to use increased carbohydrates to synthesize sesquiterpenoids.•Bacterial elicitors transform oxygen–free sesquiterpenoids to oxygenous ones.•ABC transporter substrate–binding protein induces oxygenous terpenoid formation.
Aims
The root endophyte
Phomopsis liquidambaris
B3 effectively protected peanut against root rot caused by
Fusarium oxysporum
. We investigated (i) the effects of preinoculation (before
F. oxysporum
...inoculation) and postinoculation (post
F. oxysporum
inoculation) with B3 on pathogenic infection and (ii) the potential mechanisms underlying the suppression of root rot by B3 colonization.
Methods
Peanut seedlings preinoculated, postinoculated or noninoculated with B3 and challenged or not challenged with
F. oxysporum
were cultivated in pots with sterilized vermiculite. The root rot severity, plant growth, defense-related enzyme activity and signaling compounds in plant tissues were investigated. Chemical manipulation experiments were performed to verify the signals involved in the suppression of root rot by B3.
Results
B3 preinoculation efficiently suppressed root rot, as evidenced by decreased cell death, pathogenic colonization and disease severity; however, these effects were absent in the B3 posttreated roots. B3 preinoculation locally and systemically enhanced resistance against pathogenic infection, which coincided with increased activities of pathogenesis-related proteins. These increased activities positively correlated with increased salicylic acid (SA) and hydrogen peroxide (H
2
O
2
) levels, in which SA played a dominant role.
Conclusions
Preinoculation with B3 effectively suppressed
F. oxysporum
infection in peanut roots by activating the SA-dependent defense pathway.
Jasmonic acid (JA) is a well-characterized signaling molecule in plant defense responses. However, its relationships with other signal molecules in secondary metabolite production induced by ...endophytic fungus are largely unknown. Atractylodes lancea (Asteraceae) is a traditional Chinese medicinal plant that produces antimicrobial volatiles oils. We incubated plantlets of A. lancea with the fungus Gilmaniella sp. AL12. to research how JA interacted with other signal molecules in volatile oil production.
Fungal inoculation increased JA generation and volatile oil accumulation. To investigate whether JA is required for volatile oil production, plantlets were treated with JA inhibitors ibuprofen (IBU) and nordihydroguaiaretic acid. The inhibitors suppressed both JA and volatile oil production, but fungal inoculation could still induce volatile oils. Plantlets were further treated with the nitric oxide (NO)-specific scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt (cPTIO), the H2O2 inhibitors diphenylene iodonium (DPI) and catalase (CAT), and the salicylic acid (SA) biosynthesis inhibitors paclobutrazol and 2-aminoindan-2-phosphonic acid. With fungal inoculation, IBU did not inhibit NO production, and JA generation was significantly suppressed by cPTIO, showing that JA may act as a downstream signal of the NO pathway. Exogenous H2O2 could reverse the inhibitory effects of cPTIO on JA generation, indicating that NO mediates JA induction by the fungus through H2O2-dependent pathways. With fungal inoculation, the H2O2 scavenger DPI/CAT could inhibit JA generation, but IBU could not inhibit H2O2 production, implying that H2O2 directly mediated JA generation. Finally, JA generation was enhanced when SA production was suppressed, and vice versa.
Jasmonic acid acts as a downstream signaling molecule in NO- and H2O2-mediated volatile oil accumulation induced by endophytic fungus and has a complementary interaction with the SA signaling pathway.
The endophytic fungus
Phomopsis liquidambaris
is characterized as a plant growth-promoting agent under salt stress, but its mechanism is unknown. Herein, 1-aminocyclopropane-1-carboxylate deaminase (
...ACCD
) from the strain was confirmed that it had the ability of utilizing 1-aminocyclopropane-1-carboxylate as the sole nitrogen source. The full-length
ACCD
gene was 1152 bp, which encodes a mature protein of 384 amino acids with a molecular mass of 41.53 kDa. The
ACCD
activity was 3.9-fold in 3 mmol L
−1
ACC by qRT-PCR under salt stress comparing with no salt tress. Ethylene production was increased to 34.55–70.60% and reduced the growth of rice by 23–69.73% under salt stress. Inoculation of
P. liquidambaris
increased root-shoot length, fresh and dry weight, and overall growth of stressed rice seedlings. ACC accumulation, ACC synthase and ACC oxidase activities increased in salt-treated rice seedlings, while they were significantly reduced when
P. liquidambaris
was inoculated into rice by qRT-PCR. It therefore can be concluded that
P. liquidambaris
can be used as a plant growth promoting fungus against salt stress and other biotic or abiotic stresses.
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