The effector Fg62 contributes to Fusarium graminearum virulence and induces plant cell death

Abstract

Although the functions of most protein effectors secreted by fungi are not predictable, they are known to modulate host immunity and facilitate infection. Fusarium graminearum is one of the 10 most abundant plant pathogenic fungi worldwide. To date, few effector proteins secreted by F. graminearum have been identified. In this study, we screened a putative effector protein Fg62 from proteins that contain signal peptides and unknown functional domains in F. graminearum secretome. Fg62 expression was highly upregulated during the early stages of F. graminearum infection, and its deletion reduced F. graminearum virulence in wheat and soybean. Transient expression of Fg62 or the recombinant protein led to plant cell death in Nicotiana benthamiana, and the signal peptide of Fg62 was required for cell death activation. Fg62 homologs are distributed in two species of the F. sambucinum species complex, which are also able to induce cell death in N. benthamiana. Fg62 activated plant immunity by increasing the expression of defense-related genes, and the recombinant Fg62 protein induced plant resistance to various pathogens. Overall, our results revealed that the extracellular effector Fg62 contributes to both pathogen virulence and plant immunity induction, providing new avenues for the development of environmentally friendly crop disease control strategies utilizing nonpolluting immune-inducing factors.

Identification and functional characterisation of a locus for target site integration in Fusarium graminearum

“…Currently, the well-established yeast recombinational cloning approach seems to be one of the preferred options for gene fusions in different Fg studies [ 7 – 9 ]. The methodology exploits yeast homologous recombination to fuse a gene with different promoters or tags [ 66 ].…”

“…If the protein is secreted, this extracellular targeting allows the growth of a yeast strain defective in suc2 on a sucrose selection media [ 47 ]. In Fg , validation of protein secretion is often done using the yeast secretion trap assay [ 9 , 22 , 68 ]. Even though the technique is widely accepted, these heterologous results should ideally be verified with experiments performed in the native system.…”

“…Gene complementation and protein localisation involve the stable transformation of Fg with an expression cassette. Integration of the cassette into the genome can occur by either homologous or non-homologous recombination [ 6 , 9 ]. Non-homologous recombination or ectopic integration happens when the cassette is inserted randomly into the genome.…”

“…In addition, the region should be transcriptionally active to allow proper expression of the cassette. We have observed in several studies where Fg genes functions were characterised that integration of expression cassettes occurred randomly [ 7 , 9 , 12 ]. Integrations for Fg gene complementation and protein localisation studies are usually done by ectopic integration.…”

A Bursaphelenchus xylophilus effector BxICD1 inducing plant cell death, concurrently contributes to nematode virulence and migration

“…Several other effectors, such as BxSapB1, BxSapB2, and BxSapB3, while capable of inducing plant cell death, also function as a virulence factor, during B. xylophilus infection ( Huang et al., 2019 ; Hu et al., 2019 ; Zhao et al., 2020 ). This phenomenon is relatively common in effectors from fungi and oomycetes, such as the Fusarium graminearum effector Fg62 ( Wang et al., 2023 ), the Phytophthora infestans effector Pi23226 ( Lee et al., 2023 ), etc., which can induce host cell death and promote pathogen parasitism.…”