The Pythium periplocum elicitin PpEli2 confers broad-spectrum disease resistance by triggering a novel receptor-dependent immune pathway in plants

Elicitins are microbe-associated molecular patterns produced by oomycetes to elicit plant defense.It is still unclear whether elicitins derived from non-pathogenic oomycetes can be used as bioactive molecules for disease control.Here,for the first time we identify and characterize an elicitin named PpEli2 from the soil-borne oomycete Pythium periplocum,which is a non-pathogenic mycoparasite colonizing the root ecosystem of diverse plant species.Perceived by a novel cell surface receptor-like protein,REli,that is conserved in various plants(e.g.tomato,pepper,soybean),PpEli2 can induce hypersensitive response cell death and an immunity response in Nicotiana benthamiana.Meanwhile,PpEli2 enhances the interaction between REli and its co-receptor BAK1.The receptor-dependent immune response triggered by PpEli2 is able to protect various plant species against Phytophthora and fungal infections.Collectively,our work reveals the potential agricultural application of non-pathogenic elicitins and their receptors in conferring broad-spectrum resistance for plant protection.

Plant Pathogens Utilize Effectors to Hijack the Host Endoplasmic Reticulum as Part of Their Infection Strategy

1.Introduction As the central organelle in the eukaryotic secretory pathway,the endoplasmic reticulum(ER)mediates cellular processes that include calcium homeostasis and protein processing[1,2].The infection of plants by pathogens can induce ER stress and trigger the unfolded protein response(UPR).The UPR is a conserved protective signaling pathway that leads to programmed cell death(PCD)under extreme conditions[3–5],which can harm or benefit pathogens,depending on the timing and mode of cell death,and on whether the pathogen has physiologically adapted to benefit from the dying tissue[6].The biosynthesis and proper function of plant pattern recognition receptors(PRRs),which perceive pathogen-or microbe-associated molecular patterns(PAMPs or MAMPs)at the cell surface,also rely on N-glycosylation and the ER quality-control(ERQC)system[7–9].However,pathogens have evolved the capacity utilizing effectors to bind to the host ER stress pathway and manipulate it to their advantage during infection.

Engineering crop Phytophthora resistance by targeting pathogen-derived PI3P for enhanced catabolism

Phytophthora pathogens lead to numerous economically damaging plant diseases worldwide,including potato late blight caused by P.infestans and soybean root rot caused by P.sojae.Our previous work showed that Phytophthora pathogens may generate abundant phosphatidylinositol 3-phosphate(PI3P)to promote infection via direct association with RxLR effectors.Here,we designed a disease control strategy for metabolizing pathogen-derived PI3P by expressing secreted Arabidopsis thaliana phosphatidylinositol-4-phosphate 5-kinase 1(AtPIP5K1),which can phosphorylate PI3P to PI(3,4)P2.We fused AtPIP5K1 with the soybean PR1a signal peptide(SP-PIP5K1)to enable its secretion into the plant apoplast.Transgenic soybean and potato plants expressing SP-PIP5K1 showed substantially enhanced resistance to various P.sojae and P.infestans isolates,respectively.SP-PIP5K1 significantly reduced PI3P accumulation during P.sojae and soybean interaction.Knockout or inhibition of PI3 kinases(PI3Ks)in P.sojae compromised the resistance mediated by SP-PIP5K1,indicating that SP-PIP5K1 action requires a supply of pathogen-derived PI3P.Furthermore,we revealed that SP-PIP5K1 can interfere with the action of P.sojae mediated by the RxLR effector Avr1k.This novel disease control strategy has the potential to confer durable broad-spectrum Phytophthora resistance in plants through a clear mechanism in which catabolism of PI3P interferes with RxLR effector actions.

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 Phytophthora capsid Effector Targets ACD11 Binding Partners that Regulate ROS-Mediated Defense Response in Arabidopsis

Reactive oxygen species (ROS) play a vital role in plant immune response, but the genes involved in the regulation of ROS are scantily reported. Phytophthora pathogens produce a large number of effectors to promote infection, but the modes of action adopted are largely unknown. Here, we report that RxLR207 could activate ROS-mediated cell death in Nicotiana benthamiana and was essential for virulence of P. capsici. We found that this effector targeted BPA1 (binding partner of ACD11) and four members of BPLs (BPAl-Like proteins)in Arabidopsis, and the bpa1 and bpl mutants had enhanced ROS accumulation and cell death under biotic or abiotic stresses. Furthermore, we showed that BPA1 and several BPLs functioned redundantly in plant immunity to P. capsici. We discovered that BPA1 and all six BPLs interacted with ACD11, and stabilization of ACD11 was impaired in the bpa 1, bpl2, bpl3, and bpl4 mutants. RxLR207 could promote the degradation of BPA1, BPL1, BPL2, and BPL4 to disrupt ACD11 stabilization in a 26S proteasome-dependent manner. Taken together, these fin dings indicate the important roles of Arabidopsis BPA1 and its homologs in ROS homeostasis and defense response, highlighting the usefulness of a pathogen effector-directed approach as a promising strategy for the discovery of novel plant immune regulators.

Targeting of anti-microbial proteins to the hyphal surface amplifies protection of crop plants against Phytophthora pathogens

Phytophthora pathogens are a persistent threat to the world's commercially important agricultural crops,including potato and soybean.Current strategies aim at reducing crop losses rely mostly on disease-resistance breeding and chemical pesticides,which can be frequently overcome by the rapid adaptive evolution of pathogens.Transgenic crops with intrinsic disease resista nee offer a promising alternative and con tinue to be developed.Here,we explored Phytophthora-derived PI3P(phosphatidylinositol 3-phosphate)as a novel control target,using proteins that bind this lipid to direct secreted anti-microbial peptides and proteins(AMPs)to the surface of Phytophthora pathogens.In transgenic Nicotiana benthamiana,soybean,and potato plants,significantly enhanced resistance to different pathogen isolates was achieved by expression of two AMPs(GAFP1 or GAFP3 from the Chinese medicinal herb Gastrodia elata)fused with a PI3P-specific binding domain(FYVE).Using the soybean pathogen P.sojae as an example,we demonstrated that the FYVE domain could boost the activities of GAFPs in multiple independent assays,including those performed in vitro,in vivo,and in planta.Mutational analysis of P.sojae PI3K1 and PI3K2 genes of this pathogen confirmed that the enhanced activities of the targeted GAFPs were correlated with PI3P levels in the pathogen.Collectively,our study provides a new strategy that could be used to confer resistance not only to Phytophthora pathogens in many plants but also potentially to many other kinds of plant pathogens with unique targets.

Making Use of Plant uORFs to Control Transgene Translation in Response to Pathogen Attack

Reducing crop loss to diseases is urgently needed to meet increasing food production challenges caused by the expanding world population and the negative impact of climate change on crop productivity.Disease-resistant crops can be created by expressing endogenous or exogenous genes of interest through transgenic technology.Nevertheless,enhanced resistance by overexpressing resistance-produced genes often results in adverse developmental affects.Upstream open reading frames(uORFs)are translational control elements located in the 5′untranslated region(UTR)of eukaryotic mRNAs and may repress the translation of downstream genes.To investigate the function of three uORFs from the 5′-UTR of ACCELERATED CELL 11(uORFsACD11),we develop a fluorescent reporter system and find uORFsACD11 function in repressing downstream gene translation.Individual or simultaneous mutations of the three uORFsACD11 lead to repression of downstream translation efficiency at different levels.Importantly,uORFsACD11-mediated translational inhibition is impaired upon recognition of pathogen attack of plant leaves.When coupled with the PATHOGENESIS-RELATED GENE 1(PR1)promoter,the uORFsACD11 cassettes can upregulate accumulation of Arabidopsis thaliana LECTIN RECEPTOR KINASE-VI.2(AtLecRKVI.2)during pathogen attack and enhance plant resistance to Phytophthora capsici.These findings indicate that the uORFsACD11 cassettes can be a useful toolkit that enables a high level of protein expression during pathogen attack,while for ensuring lower levels of protein expression at normal conditions.