Rhizoctonia solani transcriptional activator interacts with rice WRKY53 and grassy tiller 1 to activate SWEET transporters for nutrition

Sugars, Lipids and More: New Insights Into Plant Carbon Sources During Plant-Microbe Interactions

Heterotrophic microbes rely on host-derived carbon sources for their growth and survival. Depriving pathogens of plant carbon is therefore a promising strategy for protecting plants from disease and reducing yield losses. Importantly, this carbon starvation-mediated resistance is expected to be more broad-spectrum and durable than race-specific R-gene-mediated resistance. Although sugars are well characterized as major carbon sources for bacteria, emerging evidence suggests that plant-derived lipids are likely to be an essential carbon source for some fungal microbes, particularly biotrophs. Here, we comprehensively discuss the dual roles of carbon sources (mainly sugars and lipids) and their transport processes in immune signalling and microbial nutrition. We summarize recent findings revealing the crucial roles of lipids as susceptibility factors at all stages of pathogen infection. In particular, we discuss the potential pathways by which lipids and other plant carbon sources are delivered to biotrophs, including protein-mediated transport, vesicle trafficking and autophagy. Finally, we highlight knowledge gaps and offer suggestions for clarifying the mechanisms that underlie nutrient uptake by biotrophs, providing guidance for future research on the application of carbon starvation-mediated resistance.

Large-Scale Screening and Function Analysis of Rhizoctonia solani Effectors Targeting Rice Chloroplasts

Rice sheath blight (RSB), caused byRhizoctonia solani, is a major economic threat to global rice crops. The genome of R. solani contains over 103 potential effectors, with most functions still unknown. Previous studies show that chloroplast plays a crucial role in RSB resistance. However, whether R. solani effectors target plant chloroplasts to promote the pathogen infection remains unclear. This study leveraged four RSB-resistant chloroplast proteins to identify five interacting secreted proteins from a 430-protein R. solani yeast library. These proteins, which localize to rice chloroplasts, were shown to cause cell death in Nicotiana benthamiana and rice protoplasts, suggesting that they potentially influence host cellular processes by targeting chloroplasts. Bioinformatic analysis indicates that these five putative effectors almost all contained conserved structures related to pathogenicity. This study provides a novel method for screening specific functional effectors and facilitates the further study of the pathogenic mechanisms of R. solani.

Coexpression Regulation of New and Ancient Genes in the Dynamic Transcriptome Landscape of Stem and Rhizome Development in "Bainianzhe"-An Ancient Chinese Sugarcane Variety Ratooned for Nearly 300 Years

The sucrose yield in sugarcane largely depends on stem morphology, including length, diameter and sugar content, making sugarcane stem a key trait in breeding. The "Bainianzhe" variety from Songxi County, Fujian Province, possesses both aerial stems and rhizomes, providing a unique model for studying stem development. We performed a spatiotemporal transcriptomic analysis of the base, middle and apical sections of both aerial stems and rhizomes. The analysis categorized transcriptomes by developmental stage-base, middle and apical-rather than environmental differences. Apical segments were enriched with genes related to cell proliferation, while base segments were linked to senescence and fibrosis. Gene regulatory networks revealed key TFs involved in stem development. Orphan genes may be involved in rhizome development through coexpression networks. Plant hormones, especially genes involved in ABA and GAs synthesis, were highly expressed in rhizomes. Thiamine-related genes were also more prevalent in rhizomes. Furthermore, the apical segments of rhizomes enriched in photosynthesis-related genes suggest adaptations to light exposure. Low average temperatures in Songxi have led to unique cold acclimation in Bainianzhe, with rhizomes showing higher expression of genes linked to unsaturated fatty acid synthesis and cold-responsive calcium signalling. This indicates that rhizomes may have enhanced cold tolerance, aiding in the plant's overwintering success.

The genome sequencing and comparative genomics analysis of Rhizoctonia solani reveals a novel effector family owning a uinque domain in Basidiomycetes

Rhizoctonia solani is a soil-borne pathogen with 14 anastomosis groups (AGs), and different subgroups are genetically diverse. However, the genetic factors contributing to the pathogenicity of the fungus have not been well characterized. In this study, the genome of R. solani AG1-ZJ was sequenced. As the result, a 41.57 Mb draft genome containing 12,197 putative coding genes was obtained. Comparative genomic analysis of 11 different AGs revealed conservation and unique characteristics between the AGs. Furthermore, a novel effector family containing a 68 amino acid conserved domain unique in basidiomycetous fungi was characterized. Two effectors containing the conserved domain in AG4-JY were identified, and named as RsUEB1 and RsUEB2. Furthermore, the spray-induced gene silencing strategy was used to generate a dsRNA capable of silencing the conserved domain sequence of RsUEB1 and RsUEB2. This dsRNA can significantly reduce the expression of RsUEB1 and RsUEB2 and the pathogenicity of AG4-JY on foxtail millet, maize, rice and wheat. In conclusion, this study provides significant insights into the pathogenicity mechanisms of R. solani. The identification of the conserved domain and the successful use of dsRNA silencing of the gene containing the conserved domain will offer a new strategy for controlling sheath blight in cereal crops.

The role of sugar transporters in the battle for carbon between plants and pathogens

In photosynthetic cells, plants convert carbon dioxide to sugars that can be moved between cellular compartments by transporters before being subsequently metabolized to support plant growth and development. Most pathogens cannot synthesize sugars directly but have evolved mechanisms to obtain plant-derived sugars as C resource for successful infection and colonization. The availability of sugars to pathogens can determine resistance or susceptibility. Here, we summarize current progress on the roles of sugar transporters in plant-pathogen interactions. We highlight how transporters are manipulated antagonistically by both host and pathogens in competing for sugars. We examine the potential application of this target in resistance breeding and discuss opportunities and challenges for the future.

Advances in breeding, biotechnology, and nanotechnological approaches to combat sheath blight disease in rice

Sheath blight, caused by the fungus Rhizoctonia solani, is a major problem that significantly impacts rice production and can lead to substantial yield losses. The disease has become increasingly problematic in recent years due to the widespread use of high-yielding semi-dwarf rice cultivars, dense planting, and heavy application of nitrogenous fertilizers. The disease has become more challenging to manage due to its diverse host range and the lack of resistant cultivars. Despite utilizing traditional methods, the problem persists without a satisfactory solution. Therefore, modern approaches, including advanced breeding, transgenic methods, genome editing using CRISPR/Cas9 technology, and nanotechnological interventions, are being explored to develop rice plants resistant to sheath blight disease. This review primarily focuses on these recent advancements in combating the sheath blight disease.

Sugar Transporter HmSWEET8 Cooperates with HmSTP1 to Enhance Powdery Mildew Susceptibility in Heracleum moellendorffii Hance

The powdery mildew caused by Eeysiphe heraclei is a serious concern in Heracleum moellendorffii Hance. Therefore, exploring the mechanisms underlying sugar efflux from host cells to the fungus during the plant-fungus interaction showed great significance. The study successfully cloned HmSWEET8 and HmSTP1 genes based on RNA-seq technology. The complementation assays in yeast EBY.VW4000 found HmSWEET8 and HmSTP1 transporting hexose. Over-expressing or silencing HmSWEET8 in H. moellendorffii leaves increased or decreased powdery mildew susceptibility by changing glucose concentration in infective sites. Meanwhile, over-expressing HmSTP1 in H. moellendorffii leaves also increased powdery mildew susceptibility by elevating the glucose content of infective areas. Additionally, HmSTP1 expression was up-regulated obviously in HmSWEET8 over-expressed plants and inhibited significantly in HmSWEET8 silenced plants. Co-expressing HmSWEET8 and HmSTP1 genes significantly increased powdery mildew susceptibility compared with over-expressed HmSWEET8 or HmSTP1 plants alone. The results demonstrated that HmSTP1 may assist with HmSWEET8 to promote E. heraclei infection. Consequently, the infection caused by E. heraclei resulted in the activation of HmSWEET8, leading to an increased transfer of glucose to the apoplasmic spaces at the sites of infection, then, HmSTP1 facilitated the transport of glucose into host cells, promoting powdery mildew infection.

Design, Synthesis, Antifungal Activity, and Mechanism of Action of New Piperidine-4-carbohydrazide Derivatives Bearing a Quinazolinyl Moiety

A series of new piperidine-4-carbohydrazide derivatives bearing a quinazolinyl moiety were prepared and evaluated for their fungicidal activities against agriculturally important fungi. Among these derivatives, the chemical structure of compound A45 was clearly verified by X-ray crystallographic analysis. The antifungal bioassays revealed that many compounds in this series possessed good to excellent inhibition effects toward the tested fungi. For example, compounds A13 and A41 had EC50 values of 0.83 and 0.88 μg/mL against Rhizoctonia solani in vitro, respectively, superior to those of positive controls Chlorothalonil and Boscalid (1.64 and 0.96 μg/mL, respectively). Additionally, the above two compounds also exhibited notable inhibitory activities against Verticillium dahliae (with EC50 values of 1.12 and 3.20 μg/mL, respectively), far better than the positive controls Carbendazim and Chlorothalonil (19.3 and 11.0 μg/mL, respectively). More importantly, compound A13 could potently inhibit the proliferation of R. solani in the potted rice plants, showing good in vivo curative and protective efficiencies of 76.9% and 76.6% at 200 μg/mL, respectively. Furthermore, compound A13 demonstrated an effective inhibition of succinate dehydrogenase (SDH) activity in vitro with an IC50 value of 6.07 μM. Finally, the molecular docking study revealed that this compound could be well embedded into the active pocket of SDH via multiple noncovalent interactions, involving residues like SER39, ARG43, and GLY46.

Extracellular niche establishment by plant pathogens

The plant extracellular space, referred to as the apoplast, is inhabited by a variety of microorganisms. Reflecting the crucial nature of this compartment, both plants and microorganisms seek to control, exploit and respond to its composition. Upon sensing the apoplastic environment, pathogens activate virulence programmes, including the delivery of effectors with well-established roles in suppressing plant immunity. We posit that another key and foundational role of effectors is niche establishment - specifically, the manipulation of plant physiological processes to enrich the apoplast in water and nutritive metabolites. Facets of plant immunity counteract niche establishment by restricting water, nutrients and signals for virulence activation. The complex competition to control and, in the case of pathogens, exploit the apoplast provides remarkable insights into the nature of virulence, host susceptibility, host defence and, ultimately, the origin of phytopathogenesis. This novel framework focuses on the ecology of a microbial niche and highlights areas of future research on plant-microorganism interactions.

IDD10-NAC079 transcription factor complex regulates sheath blight resistance by inhibiting ethylene signaling in rice

INTRODUCTION

Rhizoctonia solani Kühn is a pathogen causing rice sheath blight (ShB). Ammonium transporter 1 (AMT1) promotes resistance of rice to ShB by activating ethylene signaling. However, how AMT1 activates ethylene signaling remains unclear.

OBJECTIVE

In this study, the indeterminate domain 10 (IDD10)-NAC079 interaction model was used to investigate whether ethylene signaling is modulated downstream of ammonium signaling and modulates ammonium-mediated ShB resistance.

METHODS

RT-qPCR assay was used to identify the relative expression levels of nitrogen and ethylene related genes. Yeast two-hybrid assays, Bimolecular fluorescence complementation (BiFC) and Co-immunoprecipitation (Co-IP) assay were conducted to verify the IDD10-NAC079-calcineurin B-like interacting protein kinase 31 (CIPK31) transcriptional complex. Yeast one-hybrid assay, Chromatin immunoprecipitation (ChIP) assay, and Electrophoretic mobility shift assay (EMSA) were used to verify whether ETR2 was activated by IDD10 and NAC079. Ethylene quantification assay was used to verify ethylene content in IDD10 transgenic plants. Genetic analysis is used to detect the response of IDD10, NAC079 and CIPK31 to ShB infestation.

RESULTS

IDD10-NAC079 forms a transcription complex that activates ETR2 to inhibit the ethylene signaling pathway to negatively regulating ShB resistance. CIPK31 interacts and phosphorylates NAC079 to enhance its transcriptional activation activity. In addition, AMT1-mediated ammonium absorption and subsequent N assimilation inhibit the expression of IDD10 and CIPK31 to activate the ethylene signaling pathway, which positively regulates ShB resistance.

CONCLUSION

The study identified the link between ammonium and ethylene signaling and improved the understanding of the rice resistance mechanism.

Inhibitory Activity Against Rhizoctonia Solani and Chemical Composition of Extract from Moutan Cortex

Rice sheath blight (RSB), caused by Rhizoctonia solani, is a significant disease of rice. The negative effects of chemical fungicides have created an urgent need for low-toxicity botanical fungicides. Our previous research revealed that the ethanol crude extract of Moutan Cortex (MC) exhibited superior antifungal activity against R. solani at 1000 μg/mL, resulting in a 100 % inhibition rate. The antifungal properties were mainly found in the petroleum ether extract. However, the active ingredients of the extract are still unclear. In this study, gas chromatography-mass spectrometry (GC-MS) was utilised for the analysis of its chemical components. The mycelium growth rate method was utilized to detect the antifungal activity. The findings indicated that paeonol constituted the primary active component, with a content of more than 96 %. Meanwhile, paeonol was the most significant antifungal active ingredient, the antifungal activity of paeonol (EC50=44.83 μg/mL) was much higher than that of β-sitosterol and ethyl propionate against R. solani. Observation under an optical microscope revealed that paeonol resulted in abnormal mycelial morphology. This study provided theoretical support for identifying monomer antifungal compounds and developing biological fungicides for R. solani.

Methionine biosynthetic genes and methionine sulfoxide reductase A are required for Rhizoctonia solani AG1-IA to cause sheath blight disease in rice

Rhizoctonia solani is a polyphagous necrotrophic fungal pathogen that causes sheath blight disease in rice. It deploys effector molecules as well as carbohydrate-active enzymes and enhances the production of reactive oxygen species for killing host tissues. Understanding R. solani ability to sustain growth under an oxidative-stress-enriched environment is important for developing disease control strategies. Here, we demonstrate that R. solani upregulates methionine biosynthetic genes, including Rs_MET13 during infection in rice, and double-stranded RNA-mediated silencing of these genes impairs the pathogen's ability to cause disease. Exogenous treatment with methionine restores the disease-causing ability of Rs_MET13-silenced R. solani and facilitates its growth on 10 mM H2O2-containing minimal-media. Notably, the Rs_MsrA gene that encodes methionine sulfoxide reductase A, an antioxidant enzyme involved in the repair of oxidative damage of methionine, is upregulated upon H2O2 treatment and also during infection in rice. Rs_MsrA-silenced R. solani is unable to cause disease, suggesting that it is important for the repair of oxidative damage in methionine during host colonization. We propose that spray-induced gene silencing of Rs_MsrA and designing of antagonistic molecules that block MsrA activity can be exploited as a drug target for effective control of sheath blight disease in rice.

Metabolome and Transcriptome Profiling Reveals the Function of MdSYP121 in the Apple Response to Botryosphaeria dothidea

The vesicular transport system is important for substance transport in plants. In recent years, the regulatory relationship between the vesicular transport system and plant disease resistance has received widespread attention; however, the underlying mechanism remains unclear. MdSYP121 is a key protein in the vesicular transport system. The overexpression of MdSYP121 decreased the B. dothidea resistance of apple, while silencing MdSYP121 resulted in the opposite phenotype. A metabolome and transcriptome dataset analysis showed that MdSYP121 regulated apple disease resistance by significantly affecting sugar metabolism. HPLC results showed that the levels of many soluble sugars were significantly higher in the MdSYP121-OE calli. Furthermore, the expression levels of genes related to sugar transport were significantly higher in the MdSYP121-OE calli after B. dothidea inoculation. In addition, the relationships between the MdSYP121 expression level, the soluble sugar content, and apple resistance to B. dothidea were verified in an F1 population derived from a cross between 'Golden Delicious' and 'Fuji Nagafu No. 2'. In conclusion, these results suggested that MdSYP121 negatively regulated apple resistance to B. dothidea by influencing the soluble sugar content. These technologies and methods allow us to investigate the molecular mechanism of the vesicular transport system regulating apple resistance to B. dothidea.

Starving the enemy: how plant and microbe compete for sugar on the border

As the primary energy source for a plant host and microbe to sustain life, sugar is generally exported by Sugars Will Eventually be Exported Transporters (SWEETs) to the host extracellular spaces or the apoplast. There, the host and microbes compete for hexose, sucrose, and other important nutrients. The host and microbial monosaccharide transporters (MSTs) and sucrose transporters (SUTs) play a key role in the "evolutionary arms race". The result of this competition hinges on the proportion of sugar distribution between the host and microbes. In some plants (such as Arabidopsis, corn, and rice) and their interacting pathogens, the key transporters responsible for sugar competition have been identified. However, the regulatory mechanisms of sugar transporters, especially in the microbes require further investigation. Here, the key transporters that are responsible for the sugar competition in the host and pathogen have been identified and the regulatory mechanisms of the sugar transport have been briefly analyzed. These data are of great significance to the increase of the sugar distribution in plants for improvement in the yield.

Progress in rice sheath blight resistance research

Rice sheath blight (ShB) disease poses a major threat to rice yield throughout the world. However, the defense mechanisms against ShB in rice remain largely unknown. ShB resistance is a typical quantitative trait controlled by multiple genes. With the rapid development of molecular methods, many quantitative trait loci (QTLs) related to agronomic traits, biotic and abiotic stresses, and yield have been identified by genome-wide association studies. The interactions between plants and pathogens are controlled by various plant hormone signaling pathways, and the pathways synergistically or antagonistically interact with each other, regulating plant growth and development as well as the defense response. This review summarizes the regulatory effects of hormones including auxin, ethylene, salicylic acid, jasmonic acid, brassinosteroids, gibberellin, abscisic acid, strigolactone, and cytokinin on ShB and the crosstalk between the various hormones. Furthermore, the effects of sugar and nitrogen on rice ShB resistance, as well as information on genes related to ShB resistance in rice and their effects on ShB are also discussed. In summary, this review is a comprehensive description of the QTLs, hormones, nutrition, and other defense-related genes related to ShB in rice. The prospects of targeting the resistance mechanism as a strategy for controlling ShB in rice are also discussed.