Chloroplasts are important for photosynthesis and for plant immunity against microbial pathogens. Here we identify a haustorium-specific protein (Pst_12806) from the wheat stripe rust fungus, ...Puccinia striiformis f. sp. tritici (Pst), that is translocated into chloroplasts and affects chloroplast function. Transient expression of Pst_12806 inhibits BAX-induced cell death in tobacco plants and reduces Pseudomonas-induced hypersensitive response in wheat. It suppresses plant basal immunity by reducing callose deposition and the expression of defense-related genes. Pst_12806 is upregulated during infection, and its knockdown (by host-induced gene silencing) reduces Pst growth and development, likely due to increased ROS accumulation. Pst_12806 interacts with the C-terminal Rieske domain of the wheat TaISP protein (a putative component of the cytochrome b6-f complex). Expression of Pst_12806 in plants reduces electron transport rate, photosynthesis, and production of chloroplast-derived ROS. Silencing TaISP by virus-induced gene silencing in a susceptible wheat cultivar reduces fungal growth and uredinium development, suggesting an increase in resistance against Pst infection.
Cereal rusts, caused by obligate and biotrophic fungi in the genus
Puccinia
, are important diseases that threaten world food security. With the recent discovery of alternate hosts for the stripe ...rust fungus (
Puccinia striiformis
), all cereal rust fungi are now known to be heteroecious, requiring two distinct plant species serving as primary or alternate hosts to complete their sexual life cycle. The roles of the alternate hosts in disease epidemiology and pathogen variation vary greatly from species to species and from region to region because of different climatic and cropping conditions. We focus this review on rust fungi of small grains, mainly stripe rust, stem rust, leaf rust, and crown rust of wheat, barley, oat, rye, and triticale, with emphases on the contributions of alternate hosts to the development and management of rust diseases.
Small RNAs (sRNAs), an important type of pathogenicity factor, contribute to impairing host immune responses. However, little is known about sRNAs in Puccinia striiformis f. sp. tritici (Pst), one of ...the most destructive pathogens of wheat (Triticum aestivum L.). Here, we report a novel microRNA-like RNA (milRNA) from Pst termed microRNA-like RNA 1 (Pst milR1), which suppresses wheat defenses during wheat–Pst interactions.
We identified Pst-milR1 as a novel milRNA in Pst. Biological prediction and co-transformation showed that Pst-milR1 takes part in cross-kingdom RNA interference (RNAi) events by binding the wheat pathogenesis-related 2 (PR2) gene.
Silencing of the Pst-milR1 precursor resulted in increased wheat resistance to the virulent Pst isolate CYR31. PR2 knock-down plants increased the susceptibility of wheat to the avirulent Pst isolate CYR23. This suggests that Pst-milR1 represses the plant immune response by suppressing the expression of PR2.
Taking our findings together, we postulate that Pst-milR1 is an important pathogenicity factor in Pst, which acts as an effector to suppress host immunity. Our results provide significant new insights into the pathogenicity of the stripe rust pathogen.
Abstract
Wheat rusts, including stripe, leaf, and stem rusts, are severe wheat diseases and cause huge yield loss in China annually. Benefiting from utilizing the genetic resistance wheat varieties, ...wheat stem rust has been effectively controlled since the 1970s; however, the wheat stripe and leaf rusts are still threating the wheat production in China due to lack of effective agricultural regulations. This review summarizes the research advances on wheat rust physiology, epidemiology, and fungicide resistance in China. In addition, the corresponding field management strategies for the integrated control of rust diseases are also discussed.
Cereal plants in natural ecological systems are often either sequentially or simultaneously attacked by different species of aphids, which significantly decreases the quality and quantity of ...harvested grain. The severity of the damage is potentially aggravated by microbes associated with the aphids or the coexistence of other fungal pathogens. Although chemical control and the use of cultivars with single-gene-based antibiosis resistance could effectively suppress grain aphid populations, this method has accelerated the development of insecticide resistance and resulted in pest resurgence. Therefore, it is important that effective and environmentally friendly pest management measures to control the damage done by grain aphids to cereals in agricultural ecosystems be developed and promoted. In recent decades, extensive studies have typically focused on further understanding the relationship between crops and aphids, which has greatly contributed to the establishment of sustainable pest management approaches. This review discusses recent advances and challenges related to the control of grain aphids in agricultural production. Current knowledge and ongoing research show that the integration of the large-scale cultivation of aphid-resistant wheat cultivars with agricultural and/or other management practices will be the most prevalent and economically important management strategy for wheat aphid control.
Wheat and barley are the most highly produced and consumed grains in the world. Various pathogens-viruses, bacteria, fungi, insect pests, and nematode parasites-are major threats to yield and ...economic losses. Strategies for the management of disease control mainly depend on resistance or tolerance breeding, chemical control, and biological control. The discoveries of RNA silencing mechanisms provide a transgenic approach for disease management. Host-induced gene silencing (HIGS) employing RNA silencing mechanisms and, specifically, silencing the targets of invading pathogens, has been successfully applied in crop disease prevention. Here, we cover recent studies that indicate that HIGS is a valuable tool to protect wheat and barley from diseases in an environmentally friendly way.
Stripe rust (or yellow rust), which is caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most devastating wheat diseases worldwide. The wheat cultivar Xingzi 9104 (XZ) is an elite ...wheat germplasm that possesses adult plant resistance (APR), which is non-race-specific and durable. Thus, to better understand the mechanism underlying APR, we performed transcriptome sequencing of wheat seedlings and adult plants without Pst infection, and a total of 157,689 unigenes were obtained as a reference. In total, 2,666, 783 and 2,587 differentially expressed genes (DEGs) were found to be up- or down-regulated after Pst infection at 24, 48 and 120 hours post-inoculation (hpi), respectively, based on a comparison of Pst- and mock-infected plants. Among these unigenes, the temporal pattern of the up-regulated unigenes exhibited transient expression patterns during Pst infection, as determined through a Gene Ontology (GO) enrichment analysis. In addition, a Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that many biological processes, including phenylpropanoid biosynthesis, reactive oxygen species, photosynthesis and thiamine metabolism, which mainly control the mechanisms of lignification, reactive oxygen species and sugar, respectively, are involved in APR. In particular, the continuous accumulation of reactive oxygen species may potentially contribute to the ability of the adult plant to inhibit fungal growth and development. To validate the bioinformatics results, 6 candidate genes were selected for further functional identification using the virus-induced gene silencing (VIGS) system, and 4 candidate genes likely contribute to plant resistance against Pst infection. Our study provides new information concerning the transcriptional changes that occur during the Pst-wheat interaction at the adult stage and will help further our understanding of the detailed mechanisms underlying APR to Pst.
Summary
During the infection of host plants, pathogens can deliver virulence‐associated ‘effector’ proteins to promote plant susceptibility. However, little is known about effector function in the ...obligate biotrophic pathogen Puccinia striiformis f. sp. tritici (Pst) that is an important fungal pathogen in wheat production worldwide. Here, they report their findings on an in planta highly induced candidate effector from Pst, PSTha5a23. The PSTha5a23 gene is unique to Pst and shows a low level of intra‐species polymorphism. It has a functional N‐terminal signal peptide and is translocated to the host cytoplasm after infection. Overexpression of PSTha5a23 in Nicotiana benthamiana was found to suppress the programmed cell death triggered by BAX, PAMP‐INF1 and two resistance‐related mitogen‐activated protein kinases (MKK1 and NPK1). Overexpression of PSTha5a23 in wheat also suppressed pattern‐triggered immunity (PTI)‐associated callose deposition. In addition, silencing of PSTha5a23 did not change Pst virulence phenotypes; however, overexpression of PSTha5a23 significantly enhanced Pst virulence in wheat. These results indicate that the Pst candidate effector PSTha5a23 plays an important role in plant defense suppression and rust pathogenicity, and also highlight the utility of gene overexpression in plants as a tool for studying effectors from obligate biotrophic pathogens.
Canker caused by ascomycetous Valsa species are among the most destructive diseases of woody plants worldwide. These pathogens are distinct from other pathogens because they only effectively attack ...tree bark in the field. To unravel the potential adaptation mechanism of bark colonization, we examined the genomes of Valsa mali and Valsa pyri that preferentially infect apple and pear, respectively. We reported the 44.7 and 35.7 Mb genomes of V. mali and V. pyri, respectively. We also identified the potential genomic determinants of wood colonization by comparing them with related cereal pathogens. Both genomes encode a plethora of pathogenicity‐related genes involved in plant cell wall degradation and secondary metabolite biosynthesis. In order to adapt to the nutrient limitation and low pH environment in bark, they seem to employ membrane transporters associated with nitrogen uptake and secrete proteases predominantly with acidic pH optima. Remarkably, both Valsa genomes are especially suited for pectin decomposition, but are limited in lignocellulose and cutin degradation. Besides many similarities, the two genomes show distinct variations in many secondary metabolism gene clusters. Our results show a potential adaptation of Valsa canker pathogens to colonize woody bark. Secondary metabolism gene clusters are probably responsible for this host specificity.
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