Zinc (Zn) is considered as one of the heavy metal pollutants in soil affecting agriculture. Salicylic acid (SA) is an important phytohormone that can mitigate effects against various abiotic stresses in plants, however, its exploration to improve Zn stress tolerance in alfalfa plants is still elusive. Thus, in the present study, exogenous SA treatment was conducted on alfalfa plants under Zn stress. The effects of exogenous SA on the physiological effects of alfalfa plants and the expression levels related genes were studied. This study tested the biomass, relative water content, chlorophyll levels, photosynthetic capacity, proline and soluble sugar contents, detected the activity of antioxidant enzymes (such as peroxidase and superoxide dismutase), glutathione biosynthesis, and endogenous SA levels, and quantified the genes associated with the antioxidant system and glutathione metabolism-mediated Zn stress. The results showed that exogenous SA could elevate the physiological adaptability of alfalfa plants through enhancing photosynthesis, proline and soluble sugar levels, stimulating antioxidant system and glutathione metabolism, and inducing the transcription level of related genes, thereby diminishing oxidative stress, inhibiting excessive Zn accumulation of alfalfa plants, increasing tolerance to Zn stress, and reducing the toxicity of Zn. Collectively, the application of SA alleviates Zn toxicity in alfalfa plants. The findings gave first insights into the regulatory mechanism of the Zn stress tolerance of alfalfa by exogenous SA and this might have positive implications for managing other plants which are suffering Zn stress.

Early blight (EB) disease, caused mainly byAlternaria solani, is an economic threat to potato and tomato production worldwide. Thus, accurate and sensitive detection of the fungal pathogen of this disease in plants at the early infection stage is important for forecasting EB epidemics. In this study, we developed an RNA-based method that enables highly accurate and sensitiveA. solanidetection in a whole potato leaf at a single spore level based on quantitative real-time polymerase chain reaction (qPCR). We discovered jg1677, a highly expressed gene whose full-length coding sequence is very specific forA. solani, by analyzingA. solanitranscripts isolated from enhanced high throughput transcriptome of infected potato leaves byA. solaniand using the National Center for Biotechnology Information’s basic local alignment search tool. The specificity of the primers derived from jg1677 was determined using 22 isolates of common potato pathogens, including sevenAlternariaisolates. Detecting jg1677 transcripts with qPCR is 1,295 times more sensitive than detecting genomic DNA. In addition, the expression pattern of jg1677 at different infection stages was determined by qPCR. What is more, jg1677 was expressed relatively stable between 15 and 35°C in infected leaves, and its expression was virtually unaffected in isolated leaves left at room temperature for 24 h. Our work provides a much more sensitive and accurate method compared to conditional DNA-based ones, permitting a very early diagnosis of EB and lowering the risk of EB epidemics.

Background: Alternaria solani is a typical necrotrophic pathogen that can cause severe early blight on Solanaceae crops and cause ring disease on plant leaves. Phytopathogens produce secretory effectors that regulate the host immune response and promote pathogenic infection. Effector proteins, as specialized secretions of host-infecting pathogens, play important roles in disrupting host defense systems. At present, the role of the effector secreted by A. solani during infection remains unclear. We report the identification and characterization of AsCEP112, an effector required for A. solani virulence. Result: The AsCEP112 gene was screened from the transcriptome and genome of A. solani on the basis of typical effector signatures. Fluorescence quantification and transient expression analysis showed that the expression level of AsCEP112 continued to increase during infection. The protein localized to the cell membrane of Nicotiana benthamiana and regulated senescence-related genes, resulting in the chlorosis of N. benthamiana and tomato leaves. Moreover, comparative analysis of AsCEP112 mutant obtained by homologous recombination with wild-type and revertant strains indicated that AsCEP112 gene played an active role in regulating melanin formation and penetration in the pathogen. Deletion of AsCEP112 also reduced the pathogenicity of HWC-168. Conclusion: Our findings demonstrate that AsCEP112 was an important effector protein that targeted host cell membranes. AsCEP112 regulateed host senescence-related genes to control host leaf senescence and chlorosis, and contribute to pathogen virulence.

In July 2020, potato plants (cv. Xisen 6) showing characteristic symptoms of aerial stem rot were observed in a field in Fengning Manchu Autonomous County, Chengde, Hebei Province (northern China)....

Early blight, caused by the necrotrophic fungus Alternaria solani, is an important foliar disease that causes major yield losses of potato. Effector proteins secreted by pathogens to host cells can inhibit host immune response to pathogens. Currently, the function of effector proteins secreted by A. solani during infection is poorly understood. In this study, we identified and characterized a novel candidate effector protein, AsCEP50. AsCEP50 is a secreted protein that is highly expressed throughout the infection stages of A. solani. Agrobacterium tumefaciens-mediated transient expression in Nicotiana benthamiana and tomato demonstrated that AsCEP50 is located on the plasma membrane of N. benthamiana and regulates senescence-related genes, resulting in the chlorosis of N. benthamiana and tomato leaves. Δ50 mutants were unaffected in vegetative growth, spore formation and mycelium morphology. However, the deletion of AsCEP50 significantly reduced virulence, melanin production and penetration of A. solani. These results strongly supported that AsCEP50 is an important pathogenic factor at the infection stage and contributes to the virulence of Alternaria solani.

The effectome of the necrotrophic fungal pathogen, Alternaria solani, was determined using multiomics. In total, 238 effector candidates were predicted from the A. solani genome, and apoplastic effectors constitute most of the total candidate effector proteins (AsCEPs). Comparative genomics revealed two main groups of AsCEPs: lineage-specific and conserved effectors. RNA-Seq analysis revealed that the most highly expressed genes encoding AsCEPs were enriched with lineage-specific forms. Two lineage-specific effector genes, AsCEP19 and AsCEP20, were found to form a ‘head-to-head’ gene pair located near an AT-rich region on the chromosome. To date, AsCEP19 and AsCEP20 have been found only in a few fungal species. Phylogenetic inference revealed that AsCEP19 and AsCEP20 were likely acquired by the common ancestor of A. solani and A. tomatophila via horizontal gene transfer, probably mediated by long terminal repeat retrotransposon. RT-qPCR analysis showed that AsCEP19 and AsCEP20 are tightly coexpressed in a host-specific manner and that they are upregulated at advanced stages of A. solani infection only in solanaceous hosts. Transient expression of AsCEP19 and AsCEP20 in Nicotiana benthamiana plants showed that these effectors could promote Phytophthora infestans infection. AsCEP19 and AsCEP20 were required for the full virulence of A. solani on host potato, because deletion of this gene pair significantly reduced the size of necrotic lesions on potato leaves. Transient expression of AsCEP20 could elicit plant cell death depending on the presence of its signal peptide, indicating that AsCEP20 is a necrosis-inducing apoplastic effector with the mature form localized specifically in chloroplasts. Our work provides a better understanding of the function and evolution of necrotrophic fungal effectors, and helps explain the high aggressiveness of A. solani against solanaceous crops.