Genome sequencing reveals the evolution and pathogenic mechanisms of the wheat sharp eyespot pathogen Rhizoctonia cerealis

The necrotrophic fungus Rhizoctonia cerealis is the causal agent of devastating diseases of cereal crops including wheat(Triticum aestivum).We present a high-quality genome assembly of R.cerealis Rc207,a virulent strain causing wheat sharp eyespot.The assembly(56.36 Mb)is composed of 17.87%repeat sequences and 14,433 predicted protein-encoding genes.The Rc207 genome encodes a large and diverse set of genes involved in pathogenicity,especially rich in those encoding secreted proteins,carbohydrateactive enzymes(CAZymes),peptidases,nucleases,cytochrome P450,and secondary metabolismassociated enzymes.Most secretory protein-encoding genes,including CAZymes,peroxygenases,dehydrogenases,and cytochrome P450,were up-regulated during fungal infection of wheat.We identified 831 candidate secretory effectors and validated the functions of 10 up-regulated candidate effector proteins.Of them,nine were confirmed as necrotrophic pathogen’s effectors promoting fungal infection.Abundant potential mobile or plastic genomic regions rich in repeat sequences suggest their roles in fungal adaption and virulence-associated genomic evolution.This study provides valuable resources for further comparative and functional genomics on important fungal pathogens,and provides essential tools for development of effective disease control strategies.

AlphaFold-guided redesign of a plant pectin methylesterase inhibitor for broad-spectrum disease resistance

Plant cell walls are a critical site where plants and pathogens continuously struggle for physiological domi-nance.Here we show that dynamic remodeling of pectin methylesterification of plant cell walls is a compo-nent of the physiological and co-evolutionary struggles between hosts and pathogens.A pectin methyles-terase(PsPME1)secreted by Phytophthora sojae decreases the degree of pectin methylesterification,thus synergizing with an endo-polygalacturonase(PsPG1)to weaken plant cell walls.To counter PsPME1-mediated susceptibility,a plant-derived pectin methylesterase inhibitor protein,GmPMl1,protects pectin to maintain a high methylesterification status.GmPMl1 protects plant cell walls from enzymatic degrada-tion by inhibiting both soybean and P.sojae pectin methylesterases during infection.However,constitutive expression of GmPMl1 disrupted the trade-off between host growth and defense responses.We therefore used AlphaFold structure tools to design a modified form of GmPMI1(GmPMI1R)that specifically targets and inhibits pectin methylesterases secreted from pathogens but notfrom plants.Transient expression of GmPMi1R enhanced plant resistance to oomycete and fungal pathogens.In summary,our work highlights the biochemical modification of the cell wall as an important focal point in the physiological and co-evolutionary conflict between hosts and microbes,providing an important proof of concept that Al-driven structure-based tools can accelerate the development of new strategies for plant protection.

Fusarium-produced vitamin B6 promotes the evasion of soybean resistance by Phytophthora sojae

Plants can be infected by multiple pathogens concurrently in natural systems. However,pathogen–pathogen interactions have rarely been studied. In addition to the oomycete Phytophthora sojae, fungi such as Fusarium spp. also cause soybean root rot. In a 3-year field investigation, we discovered that P. sojae and Fusarium spp. frequently coexisted in diseased soybean roots. Out of 336 P. sojae–soybean–Fusarium combinations,more than 80% aggravated disease. Different Fusarium species all enhanced P. sojae infection when co-inoculated on soybean. Treatment with Fusarium secreted non-proteinaceous metabolites had an effect equal to the direct pathogen coinoculation. By screening a Fusarium graminearum mutant library, we identified Fusarium promoting factor of Phytophthora sojae infection 1(Fpp1),encoding a zinc alcohol dehydrogenase. Fpp1 is functionally conserved in Fusarium and contributes to metabolite-mediated infection promotion, in which vitamin B6(VB6) produced by Fusarium is key. Transcriptional and functional analyses revealed that Fpp1 regulates two VB6 metabolism genes, and VB6 suppresses expression of soybean disease resistance-related genes. These results reveal that co-infection with Fusarium promotes loss of P. sojae resistance in soybean, information that will inform the sustainable use of diseaseresistant crop varieties and provide new strategies to control soybean root rot.

Phytophthora sojae Effector PsAvh240 Inhibits Host Aspartic Protease Secretion to Promote Infection

Plants secrete defense molecules into the extracellular space (the apoplast) to combat attacking microbes. However, the mechanisms by which successful pathogens subvert plant apoplastic immunity remain poorly understood. In this study, we show that PsAvh240, a membrane-localized effector of the soybean pathogen Phytophthora sojae, promotes P. sojae infection in soybean hairy roots. We found that PsAvh240 interacts with the soybean-resistant aspartic protease GmAP1 in planta and suppresses the secretion of GmAP1 into the apoplast. By solving its crystal structure we revealed that PsAvh240 contain six a helices and two WY motifs. The first two a helices of PsAvh240 are responsible for its plasma membrane-localization and are required for PsAvh240's interaction with GmAP1. The second WY motifs of two PsAvh240 molecules form a handshake arrangement resulting in a handshake-like dimer. This dimerization is required for the effector's repression of GmAP1 secretion. Taken together, these data reveal that PsAvh240 localizes at the plasma membrane to interfere with GmAP1 secretion, which represents an effective mechanism by which effector proteins suppress plant apoplastic immunity.

A new distinct geminivirus causes soybean stay-green disease

Dear Editor,Plant viruses make up almost half of the plant disease-causing pathogens,affecting crop yields and the global economy(Savary et al.,2019).Soybean(Glycine max)is one of the most valuable legume crops in the world,supplying 25%of the global edible oil and two-thirds of the global concentrated protein for livestock feeding.Recently,the outbreak of soybean stay-green syndrome with delayed leaf senescence(stay-green),flat pods,and increased number of abnormal seeds has swept the soybean production in the Huang-Huai-Hai region of China,resulting in huge yield losses(Xu et al.,2019).This disease has become an epidemic and prominent problem in soybean production and is still expanding its geography,including North America,posing a serious threat to soybean production(Harbach et al.,2016;Zhang et al.,2016;Li et al.,2019).However,the cause of soybean stay-green syndrome remains obscure.

The Phytophthora effector Avh241 interacts with host NDR1-like proteins to manipulate plant immunity

Plant pathogens rely on effector proteins to suppress host innate immune responses and facilitate colonization.Although the Phytophthora sojae RxLR effector Avh241 promotes Phytophthora infection,the molecular basis of Avh241 virulence remains poorly understood.Here we identified non-race specific disease resistance 1(NDR1)-like proteins,the critical components in plant effector-triggered immunity(ETI)responses,as host targets of Avh241.Avh241 interacts with NDR1 in the plasma membrane and suppresses NDR1-participated ETI responses.Silencing of GmNDR1s increases the susceptibility of soybean to P.sojae infection,and overexpression of GmNDR1s reduces infection,which supports its positive role in plant immunity against P.sojae.Furthermore,we demonstrate that GmNDR1 interacts with itself,and Avh241 probably disrupts the self-association of GmNDR1.These data highlight an effective counter-defense mechanism by which a Phytophthora effector suppresses plant immune responses,likely by disturbing the function of NDR1 during infection.

Fg12 ribonuclease secretion contributes to Fusarium graminearum virulence and induces plant cell death

Filamentous fungal pathogens secrete effectors that modulate host immunity and facilitate infection. Fusarium graminearum is an important plant pathogen responsible for various devastating diseases. However, little is known about the function of effector proteins secreted by F. graminearum. Herein, we identified several effector candidates in the F. graminearum secretome. Among them, the secreted ribonuclease Fg12 was highly upregulated during the early stages of F. graminearum infection in soybean;its deletion compromised the virulence of F. graminearum. Transient expression of Fg12 in Nicotiana benthamiana induced cell death in a light-dependent manner. Fg12 possessed ribonuclease(RNase) activity, degrading total RNA. The enzymatic activity of Fg12 was required for its cell death-promoting effects. Importantly, the ability of Fg12 to induce cell death was independent of BAK1/SOBIR1, and treatment of soybean with recombinant Fg12 protein induced resistance to various pathogens, including F. graminearum and Phytophthora sojae. Overall, our results provide evidence that RNase effectors not only contribute to pathogen virulence but also induce plant cell death.