Pseudomonas syringae, a major hemibiotrophic bacterial pathogen, causes many devastating plant diseases. However, the transcriptional regulation of plant defense responses to P. syringae remains largely unknown. Here, we found that gain-of-function of BTB AND TAZ DOMAIN PROTEIN 4 (BT4) enhanced the resistance of Arabidopsis (Arabidopsis thaliana) to Pst DC3000 (Pseudomonas syringae pv. tomato DC3000). Disruption of BT4 also weakened the salicylic acid (SA)-induced defense response to Pst DC3000 in bt4 mutants. Further investigation indicated that, under Pst infection, transcription of BT4 is modulated by components of both the SA and ethylene (ET) signaling pathways. Intriguingly, the specific binding elements of ETHYLENE RESPONSE FACTOR (ERF) proteins, including dehydration responsive/C-repeat elements and the GCC box, were found in the putative promoter of BT4. Based on publicly available microarray data and transcriptional confirmation, we determined that ERF11 is inducible by salicylic acid and Pst DC3000 and is modulated by the SA and ET signaling pathways. Consistent with the function of BT4, loss-of-function of ERF11 weakened Arabidopsis resistance to Pst DC3000 and the SA-induced defense response. Biochemical and molecular assays revealed that ERF11 binds specifically to the GCC box of the BT4 promoter to activate its transcription. Genetic studies further revealed that the BT4-regulated Arabidopsis defense response to Pst DC3000 functions directly downstream of ERF11. Our findings indicate that transcriptional activation of BT4 by ERF11 is a key step in SA/ET-regulated plant resistance against Pst DC3000, enhancing our understanding of plant defense responses to hemibiotrophic bacterial pathogens.

The secretory proteome plays an important role in the pathogenesis of phytopathogenic fungi. However, the relationship between the large-scale secretome of phytopathogenic fungi and their lifestyle is not fully understood. In the present study, the secretomes of 150 plant pathogenic fungi were predicted and the characteristics associated with different lifestyles were investigated. In total, 94,974 secreted proteins (SPs) were predicted from these fungi. The number of the SPs ranged from 64 to 1,662. Among these fungi, hemibiotrophic fungi had the highest number (average of 970) and proportion (7.1%) of SPs. Functional annotation showed that hemibiotrophic and necrotroph fungi, differ from biotrophic and symbiotic fungi, contained much more carbohydrate enzymes, especially polysaccharide lyases and carbohydrate esterases. Furthermore, the core and lifestyle-specific SPs orthogroups were identified. Twenty-seven core orthogroups contained 16% of the total SPs and their motif function annotation was represented by serine carboxypeptidase, carboxylesterase and asparaginase. In contrast, 97 lifestyle-specific orthogroups contained only 1% of the total SPs, with diverse functions such as PAN_AP in hemibiotroph-specific and flavin monooxygenases in necrotroph-specific. Moreover, obligate biotrophic fungi had the largest number of effectors (average of 150), followed by hemibiotrophic fungi (average of 120). Among these effectors, 4,155 had known functional annotation and pectin lyase had the highest proportion in the functionally annotated effectors. In addition, 32 sets of RNA-Seq data on pathogen-host interactions were collected and the expression levels of SPs were higher than that of non-SPs, and the expression level of effector genes was higher in biotrophic and hemibiotrophic fungi than in necrotrophic fungi, while secretase genes were highly expressed in necrotrophic fungi. Finally, the secretory activity of five predicted SPs from Setosphearia turcica was experimentally verified. In conclusion, our results provide a foundation for the study of pathogen-host interaction and help us to understand the fungal lifestyle adaptation.

Fusarium diseases, including corn root rot, sheath rot, stalk rot, and ear rot are frequently occurring in maize producing areas of China. Fusarium stalk rot and ear rot are the most serious diseases and often occur at the same time, but it is unclear whether there is a correlation between Fusarium composition and disease occurrence. This study was conducted to clarify the relationship between the two diseases. A total of 49 corn stalk rot samples were collected from 15 regions of eight provinces in China from 2016 to 2018. The pathogens were isolated and identified separately from stalks, ear stems, and kernels. The contents of the fumonisins (FB₁ and FB₂) were detected in kernels. The results showed that the main Fusarium species were found in corn kernels, ear stems and stalks at the same time. The results showed that 1201 strains of Fusarium verticillioides, 668 strains of Fusarium oxysporum, 574 strains of Fusarium graminearum species complex (FGSC), 318 strains of Fusarium equiseti, 95 strains of Fusarium proliferatum, and 40 strains of Fusarium subglutinans were isolated from 1470 corn kernels, 245 ear stems, and 1225 stalks randomly selected from 49 samples. The contamination rate of fumonisins in the 49 samples was 57.1% with an average content of 1.9 μg/g, of which four samples exhibited higher levels as set by the European Commission (4.0 μg/g). These results provide a certain association between stalk rot and ear rot and lay a foundation to study the relationships among Fusarium maize diseases.

Fusarium graminearum is the causal agent of Gibberella stalk rot in maize stem, resulting in maize lodging, yield, quality, and mechanical harvesting capacity. To date, little is known about the maize stem defense mechanism in response to the invasion of F. graminearum. This study represents a global proteomic approach to document the infection by F. graminearum. A total of 1,894 differentially expressed proteins (DEPs) were identified in maize stem with F. graminearum inoculation. Functional categorization analysis indicated that proteins involved in plant-pathogen interaction were inducible at the early stages of infection. We also found that the expression of proteins involved in phenylpropanoid, flavonoid, and terpenoid biosynthesis were upregulated in response to F. graminearum infection, which may reflect that these secondary metabolism pathways were important in the protection against the fungal attack in maize stem. In continuously upregulated proteins after F. graminearum infection, we identified a WRKY transcription factor, ZmWRKY83, which could improve the resistance to plant pathogens. Together, the results show that the defense response of corn stalks against F. graminearum infection was multifaceted, involving the induction of proteins from various immune-related pathways, which had a directive significance for molecular genetic breeding of maize disease-resistant varieties.