Chao Han

Pattern-triggered immunity (PTI), the first line of defense in plants, is activated when host pattern recognition receptors (PRRs) detect pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs) released during microbial invasion. Over the past decade, major advances have clarified PTI’s complex signaling network, revealing its role as a dynamic regulator of plant immune responses. This review summarizes recent progress in PTI signal transduction, emphasizing the core mechanisms: (1) kinase cascades, including MAPKs and calcium-dependent protein kinases (CDPKs), that amplify defense signals; (2) calcium ion (Ca2+) dynamics acting as rapid secondary messengers; and (3) reactive oxygen species (ROS) bursts that mediate antimicrobial and signaling. The roles of lipid signaling, crosstalk between immune signaling and plant hormones, and scaffold proteins are also discussed. Furthermore, we explore the interplay between PTI and effector-triggered immunity (ETI), highlighting synergistic modules, such as the enhanced disease susceptibility 1–phytoalexin deficient 4–activated disease resistance 1 (EDS1-PAD4-ADR1) which integrate immune signals to enhance pathogen resistance. By linking molecular mechanisms to systemic immune regulation, this review provides a comprehensive framework for understanding plant defense strategies and identifies emerging opportunities to engineer disease-resistant crops through modulation of immune pathways.

Background: Lignocellulose is the most abundant natural biomass resource for the production of biofuels and other chemicals. The efficient degradation of cellulose by cellulases is a critical step for the lignocellulose bioconversion. Understanding the structure-catalysis relationship is vital for rational design of more stable and highly active enzymes. Glycoside hydrolase (GH) family 5 is the largest and most functionally diverse group of cellulases, with a conserved TIM barrel structure. The important roles of the various loop regions of GH5 enzymes in catalysis, however, remain poorly understood. Results: In the present study, we investigated the relationship between the loops surrounding active site architecture and its catalytic efficiency, taking TfCel5A, an enzyme from GH5_2 subfamily of Thermobifida fusca, as an example. Large-scale computational simulations and site-directed mutagenesis experiments revealed that three loops (loop 8, 3, and 7) around active cleft played diverse roles in substrate binding, intermediate formation, and product release, respectively. The highly flexible and charged residue triad of loop 8 was responsible for capturing the ligand into the active cleft. Severe fluctuation of loop 3 led to the distortion of sugar conformation at the − 1 subsite. The wobble of loop 7 might facilitate product release, and the enzyme activity of the mutant Y361W in loop 7 was increased by approximately 40%. Conclusion: This study unraveled the vital roles of loops in active site architecture and provided new insights into the catalytic mechanism of the GH5_2 cellulases.

Lysobacter capsici X2-3, a plant growth-promoting rhizobacteria (PGPR), was isolated from wheat rhizosphere and has inhibitory effects against a wide range of pathogens. One important characteristic of L. capsici is its ability to produce diverse antibiotics and lytic enzymes. The GntR family of transcription factors is a common transcription factor superfamily in bacteria that has fundamental roles in bacterial metabolism regulation. However, the GntR family transcription factor in Lysobacter has not been identified. In this study, to obtain an understanding of the GntR/HutC gene function in L. capsici X2-3, a random Tn5-insertion mutant library of X2-3 was constructed to select genes showing pleiotropic effects on phenotype. We identified a Tn5 mutant with an insertion in LC4356 that showed reduced biofilm levels, and sequence analysis indicated that the inserted gene encodes a GntR/HutC family transcription regulator. Furthermore, the LC4356 mutant showed reduced extracellular polysaccharide (EPS) production, diminished twitching motility and decreased survival under UV radiation and high-temperature. The RT‒qPCR results indicated that the pentose phosphate pathway-related genes G6PDH, 6PGL and PGDH were upregulated in the LC4356 mutant. Thus, since L. capsici is an efficient biocontrol agent for crop protection, our findings provide fundamental insights into GntR/HutC and will be worthwhile to improve PGPR biocontrol efficacy.

Southern blight, stem rot, and root rot are serious soil-borne fungal diseases of peanut, which are caused by Sclerotium rolfsii, Lasiodiplodia theobromae, and Fusarium oxysporum, respectively. These diseases are difficult to be diagnosed in early stage of infection, causing the optimal treatment period was often missed. Therefore, establishing a rapid detection system is of great significance for early prevention of peanut soil-borne fungal diseases. Here, we have invented a multiplex PCR detection system to detect fungal pathogens of peanut southern blight, stem rot, and root rot at the same time. The quarantine fungal pathogen primer pairs were amplified to the specific number of base pairs in each of the following fungal pathogens: 1005-bp (F. oxysporum), 238-bp (L. theobromae), and 638-bp (S. rolfsii). The detection limit for the single and multiplex PCR primer sets was 1 ng of template DNA under in vitro conditions. Amplification of fungi of non-target species yielded no non-specific products. The validation showed that the multiplex PCR could effectively detect single and mixed infections in field samples. Overview, this study proved that this mPCR assay was a rapid, reliable, and simple tool for the simultaneous detection of three important peanut soil-borne diseases, which facilitated prompt treatment and prevention of peanut root diseases.

Cynanchum paniculatum is a valuable medicinal herb used for the effective treatment of various human ailments. A severe anthracnose disease of C. paniculatum was recently observed in Tai’an, China, which caused considerable economic losses in this main herb-growing region of northern China. Infected plants had conspicuous symptoms consisting of circular brown lesions on the leaves and pods, as well as light brown cankers with dark spines on the stem surface. Fungi were isolated from diseased plant tissues, which exhibited radial colony morphology with dense white mycelial growth on potato dextrose agar. Through morphological observation and multigene sequencing analysis of the ITS region and actin, β-tubulin and histone genes, the isolated fungi were identified as Colletotrichum truncatum. Pathogenicity tests were conducted resulting in symptoms on C. paniculatum similar to those seen in the field. Considering the fungal species in the genus Colletotrichum are major phytopathogens that can cause serious anthracnose diseases on numerous crop species, the pathogenicity of an isolate of C. truncatum was assessed on multiple plant species. This is the first report of C. truncatum causing anthracnose of the Chinese medicinal herb C. paniculatum.

Glucose-inhibited division protein (GidA) plays a critical role in the growth, stress response, and virulence of bacteria. However, how gidA may affect plant growth-promoting bacteria (PGPB) is still not clear. Our study aimed to describe the regulatory function of the gidA gene in Lysobacter capsici, which produces a variety of lytic enzymes and novel antibiotics. Here, we generated an LC_GidA mutant, MT16, and an LC_GidA complemented strain, Com-16, by plasmid integration. The deletion of LC_GidA resulted in an attenuation of the bacterial growth rate, motility, and biofilm formation of L. capsici. Root colonization assays demonstrated that the LC_GidA mutant showed reduced colonization of wheat roots. In addition, disruption of LC_GidA showed a clear diminution of survival in the presence of high temperature, high salt, and different pH conditions. The downregulated expression of genes related to DNA replication, cell division, motility, and biofilm formation was further validated by real-time quantitative PCR (RT–qPCR). Together, understanding the regulatory function of GidA is helpful for improving the biocontrol of crop diseases and has strong potential for biological applications.

Phytopathogens deploy glycoside hydrolases (GHs) to disintegrate plant cell walls for nutrition and invasion. However, the pathogenic mechanisms of the majority of GHs in virulence remain unknown, especially in oomycetes. In this study, a Phytophthora sojae gene encodes a GH7 family cellobiohydrolase, named PsGH7a, was identified. PsGH7a was highly induced during the cyst germination and infection stages. PsGH7a is conserved in oomycetes, and shares a high amino acid sequence identity (>85%) within Phytophthora genus. The recombinant PsGH7a catalyzes the hydrolysis of β-1,4-glucan and avicel, which represent the major components of cellulose in plant cell wall. The mutation of catalytic residue Glu236 to alanine resulted in a lower catalytic activity. In addition, the PsGH7a promotes Phytophthora invasion, while the mutant can not. Notably, PsGH7a protein triggers hypersensitive cell death in diverse plants. PsGH7a knockout mutants were generated via CRISPR/Cas9 system, to investigate its biological function. Compared to wild-type strain P6497, the mutants showed reduced virulence on susceptible soybean, indicates PsGH7a is indispensable to P. sojae virulence.