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Summary: Pathogenic fungi such as Valsa mali secrete effector proteins to manipulate host defenses and facilitate infection. Subtilases are identified as potential virulence factors, yet their specific roles in fruit tree pathogens, such as those affecting apple trees, are poorly understood.Our research shows VmSpm1 as a virulence factor in V. mali. Knocking it out decreased virulence, whereas its heterologous expression in apple led to reduced disease resistance.Using Y2H, BiFC, SLC, and Co‐IP techniques, we demonstrated an interaction between VmSpm1 and MdPYL4. MdPYL4 levels increased during V. mali infection. The stable transgenic apple lines inoculation experiment showed that MdPYL4 correlates with enhanced resistance to Apple Valsa canker when overexpressed in apples. Furthermore, through in vitro and in vivo assays, we showed the degradative role of VmSpm1 on MdPYL4. MdPYL4 promotes the synthesis of jasmonic acid (JA) in apples in an abscisic acid‐dependent manner. The degradation of MdPYL4 leads to a reduction in JA content in apples during V. mali infection, thereby impairing JA signal transduction and decreasing disease resistance in apple plants.In summary, this study reveals how V. mali utilizes VmSpm1 to subvert JA signaling, shedding light on fungal manipulation of plant hormones to disrupt immunity. [ABSTRACT FROM AUTHOR]

Valsa mali is a destructive phytopathogenic fungus that mainly infects apple and pear trees. Infection with V. mali results in host tissue acidification via the generation of citric acid, which promote invasion. Here, two plasma membrane H+-ATPases, VmPma1 and VmPma2 , were identified in V. mali. The VmPma1 deletion mutant (∆VmPma1) displayed higher intracellular acid accumulation and a lower growth rate compared to the wild type. In contrast, the VmPma2 deletion mutant (∆VmPma2) showed no obvious phenotypic differences. Meanwhile, loss of VmPma1 , but not VmPma2 , in V. mali led to a significant decrease in growth under acidic or alkaline conditions compared with WT. More importantly, ∆VmPma1 showed a greater reduction in ATPase hydrolase activity and acidification of the external environment, more sensitivity to abiotic stress, and weaker pathogenicity than ∆VmPma2. This evidence indicates that VmPma1 is the main gene of the two plasma membrane H+-ATPases. Transcriptomic analysis indicated that many metabolic processes regulated by VmPma1 are strictly pH-regulated. Besides, we identified two genes (named VmAgn1p and Vmap1) that contribute to the pathogenicity of V. mali by differentially regulating external acidification capacity. Overall, our findings show that VmPma1 plays a pivotal role in pathogenicity by affecting the acidification of V. mali. [ABSTRACT FROM AUTHOR]

Plant growth-promoting rhizobacteria (PGPR) have been reported to suppress various diseases as potential bioagents. It can inhibit disease occurrence through various means such as directly killing pathogens and inducing systemic plant resistance. In this study, a bacterium isolated from soil showed significant inhibition of Valsa mali. Morphological observations and phylogenetic analysis identified the strain as Pseudomonas thivervalensis , named K321. Plate confrontation assays demonstrated that K321 treatment severely damaged V. mali growth, with scanning electron microscopy (SEM) observations showing severe distortion of hyphae due to K321 treatment. In vitro twigs inoculation experiments indicated that K321 had good preventive and therapeutic effects against apple Valsa canker (AVC). Applying K321 on apples significantly enhanced the apple inducing systemic resistance (ISR), including induced expression of apple ISR-related genes and increased ISR-related enzyme activity. Additionally, applying K321 on apples can activate apple MAPK by enhancing the phosphorylation of MPK3 and MPK6. In addition, K321 can promote plant growth by solubilizing phosphate, producing siderophores, and producing 3-indole-acetic acid (IAA). Application of 0.2% K321 increased tomato plant height by 53.71%, while 0.1% K321 increased tomato fresh weight by 59.55%. Transcriptome analysis revealed that K321 can inhibit the growth of V. mali by disrupting the integrity of its cell membrane through inhibiting the metabolism of essential membrane components (fatty acids) and disrupting carbohydrate metabolism. In addition, transcriptome analysis also showed that K321 can enhance plant resistance to AVC by inducing ISR-related hormones and MAPK signaling, and application of K321 significantly induced the transcription of plant growth-related genes. In summary, an excellent biocontrol strain has been discovered that can prevent AVC by inducing apple ISR and directly killing V. mali. This study indicated the great potential of P. thivervalensis K321 for use as a biological agent for the control of AVC. [Display omitted] • K321 induces V. mali membrane disruption by altering V. mali fatty acid metabolism. • K321 exhibits both excellent protective and therapeutic effects against AVC. • K321 enhances apple resistance to AVC by inducing ISR. • K321 can significantly promote plant growth through multiple mechanisms. [ABSTRACT FROM AUTHOR]

Apple Valsa canker caused by the pathogenic fungus Valsa mali , are one of the most destructive diseases of woody plants worldwide. One rhizosphere microbe strain, designated as T27 and subsequently identified as Bacillus vallismortis based on morphological and phylogenetic analyses, was studied as a potential biocontrol agent. Inoculation assay showed the B. vallismortis T27 suppressed the mycelial growth of V. mali with 81.33% antifungal effect on dual culture plates and caused hyphal deformities, wrinkles. The T27 fermentation broth significantly suppress the fungi's ability to acidify the surrounding environment. The addition of T27 cell-free supernatant (CFS) caused the pH of the fungal culture medium to increase from 3.60 to 5.10. B. vallismortis T27 showed the presence of Surfactin, IturinA and Bacilysin antimicrobial biosynthetic genes by the PCR assay. In addition, the B. vallismortis T27 was able to promote plant growth by producing siderophores and solubilizing phosphorus. The application of 2% fermentation broth of T27 resulted in a significant increase of 55.99% in the height of tomato plants and a 33.03% increase in the fresh weight of tomatoes. Under laboratory and field conditions, the B. vallismortis T27 exhibited strong antifungal activities on detached twigs and intact plants. The treatment of T27 resulted in a 35.9% reduction in lesion area on detached twigs. Furthermore, when applied to intact plants, T27 demonstrated a scar healing rate of 85.7%, surpassing the 77.8% observed in the treatment with tebuconazole. Comparative transcriptome analysis showed down-regulation of the genes associated with the fungal cell wall and cell membrane's synthesis and composition during V. mali treated with the B. vallismortis T27. In addition, gene transcription level analysis under treatment with B. vallismortis T27 revealed a significant increase in the expression levels of genes associated with diterpene biosynthesis, alanine, aspartic acid and glutamate metabolism, and plant hormone signaling in the apple, consistent with qRT-PCR and RNA-seq results. In this study, B. vallismortis T27 isolated from rhizosphere soil and identified as a novel biological control agent against apple Valsa canker. It exhibited effectively control over Valsa canker through multiple mechanisms, including disrupting the fungal cell membrane structure, altering the fungal growth environment, activating the plant MAPK pathway, and inducing upregulation of plant terpene biosynthetic genes. These findings highlight the potential of B. vallismortis T27 as a promising and multifaceted approach for managing apple Valsa canker. [Display omitted] • T27 has strongly effective against Valsa canker caused by V. mali in both laboratory and field conditions. • 16% T27 cell-free supernatant exhibits a complete inhibitory effect on Valsa mali hyphae growth. • T27 can damage the membrane of fungal cells, resulting in cell death. • Lipopeptide were found to be produced by T27, which play a major role in antifungal activity. • T27 enhances plant resistance by up-regulating expression ofphytoalexins synthesis gene and activating MAPK pathway. [ABSTRACT FROM AUTHOR]