Summary: To defend against pathogens, plants have developed a complex immune system, which recognizes the pathogen effectors and mounts defence responses. In this study, the p33 protein of Citrus tristeza virus (CTV), a viral membrane‐associated effector, was used as a molecular bait to explore virus interactions with host immunity. We discovered that Citrus macrophylla miraculin‐like protein 2 (CmMLP2), a member of the soybean Kunitz‐type trypsin inhibitor family, targets the viral p33 protein. The expression of CmMLP2 was up‐regulated by p33 in the citrus phloem‐associated cells. Knock‐down of the MLP2 expression in citrus plants resulted in a higher virus accumulation, while the overexpression of CmMLP2 reduced the infectivity of CTV in the plant hosts. Further investigation revealed that, on the one hand, binding of CmMLP2 interrupts the cellular distribution of p33 whose proper function is necessary for the effective virus movement throughout the host. On the other hand, the ability of CmMLP2 to reorganize the endomembrane system, amalgamating the endoplasmic reticulum and the Golgi apparatus, induces cellular stress and accumulation of the reactive oxygen species, which inhibits the replication of CTV. Altogether, our data suggest that CmMLP2 employs a two‐way strategy in defence against CTV infection.

Cytospora mali is an important factor for apple valsa canker, and Bacillus veleznesis L-1 is an effective biocontrol agent against apple valsa canker. Quantitative acetyl-proteomics is known to regulate transcriptional activity in different organisms; limited knowledge is available for acetylation modification in C. mali, and its response to biocontrol agents. In this study, using Tandem Mass tag proteomic strategies, we identified 733 modification sites on 416 proteins in C. mali, functions of these proteins were analyzed using GO enrichment and KEGG pathway. Some lysine acetylated proteins are found to be important to the fungal pathogenicity of C. mali, and also the response of fungi to biostress. B. velezensis L-1 suppressed the C. mali QH2 by causing the energy shortage and reduced virulence. Correspondingly, the C. mali QH2 could alleviate the suppression of biostress by upregulation of autophagy, peroxidase, cytochrome P450, ABC transporter and Heat shock protein 70. In summary, our results provided the first lysine acetylome of C. mali and its response to B. velezensis L-1.

White clover (Trifolium repens L.) is an important perennial legume forage and ornamental plant, and is widely distributed and cultivated in the world. Recently, white clover plants showing symptoms of leaf mosaic and redding were observed in Hohhot, Inner Mongolia of China. In this work, flexuous filamentous viral particles of about 700 × 13 nm in size were observed in the symptomatic leaf samples. The infection of clover yellow vein virus (ClYVV) was confirmed by small RNA sequencing and RT-PCR validation. Mechanical inoculation assays showed that this ClYVV isolate (ClYVV-IM) can infect a range of herbaceous species, including Nicotiana benthamiana, N. occidentalis, Chenopodium quinoa, C. amaranticolor, Vicia faba, Vigna unguiculata, and Solanum lycopersicum, causing various symptoms. The complete genome sequence of ClYVV-IM consists of 9565 nt and shared sequence identities, ranging from 83.05% to 96.30%, with those of the other ClYVV isolates published in GenBank. Phylogenetic analyses based on the polyprotein nucleotide and amino acid sequences clustered 15 ClYVV isolates into two groups and ClYVV-IM located in Group I. Two potential recombination events located at 914–2970 nt and 5153–5694 nt were detected in the genome of ClYVV-IM. To our knowledge, this is the first report of occurrence and complete genome of ClYVV infecting white clover in China.

Bean common mosaic virus (BCMV) was detected on common bean (Phaseolus vulgaris) plants showing wrinkled and/or narrow leaves, curling, shrinking and chlorosis of leaves, dwarfing of plants, and mottled pods in Inner Mongolia and named BCMV-22Huhe. Its genome has a size of 10,062 bp and was deposited in GenBank under the accession number OR778613. It is closely related to BCMV-Az (GenBank accession no. KP903372, in China) in the lineage of AzBMV. A recombination event was detected for BCMV-22Huhe among the 99 BCMV isolates published in the NCBI GenBank database, showing that BCMV-CJ25 (MK069986, found in Mexico) was a potential major parent, and the minor parent is unknown. This work is the first description of the occurrence of BCMV in Inner Mongolia, China.