Fol‐milR1, a pathogenicity factor of Fusarium oxysporum, confers tomato wilt disease resistance by impairing host immune responses

Abstract

Although it is well known that miRNAs play crucial roles in multiple biological processes, there is currently no evidence indicating that milRNAs from Fusarium oxysporum f. sp. lycopersici (Fol ) interfere with tomato resistance during infection.Here, using sRNA-seq, we demonstrate that Fol-milR1, a trans-kingdom small RNA, is exported into tomato cells after infection.The knockout strain ΔFol-milR1 displays attenuated pathogenicity to the susceptible tomato cultivar 'Moneymaker'. On the other hand, Fol-milR1 overexpression strains exhibit enhanced virulence against the resistant cultivar 'Motelle'. Several tomato mRNAs are predicted targets of Fol-milR1. Among these genes, Solyc06g007430 (encoding the CBLinteracting protein kinase, SlyFRG4) is regulated at the posttranscriptional level by Fol-milR1. Furthermore, SlyFRG4 loss-of-function alleles created using CRISPR/Cas9 in tomato ('Motelle') exhibit enhanced disease susceptibility to Fol, further supporting the idea that SlyFRG4 is essential for tomato wilt disease resistance. Notably, our results using immunoprecipitation with specific antiserum suggest that Fol-milR1 interferes with the host immunity machinery by binding to tomato ARGONAUTE 4a (SlyAGO4a). Furthermore, virus-induced gene silenced (VIGS) knock-down SlyAGO4a plants exhibit reduced susceptibility to Fol.Together, our findings support a model in which Fol-milR1 is an sRNA fungal effector that suppresses host immunity by silencing a disease resistance gene, thus providing a novel virulence strategy to achieve infection.

Biogenesis, Trafficking, and Function of Small RNAs in Plants

“…This mechanism has been discovered in plants such as sunflower, tomato and olive, indicating that the precise cross-kingdom targeting transport of plant sRNA is mediated by EV ( Prado et al, 2014 ; Regente et al, 2017 ; De Palma et al, 2020 ; Figure 2C , I). In addition, fungi, bacterial and parasitic plants can also transport sRNA or genes into plants as one of the sources of vsiRNA ( Shahid et al, 2018 ; Dunker et al, 2020 ; Ji et al, 2021 ; Figures 1D , 2C , I).…”

“…Dual-luciferase reporter assay, gene transient expression analysis, and degradome sequencing are usually used to verify sRNA binding sites ( Hu et al, 2020 ; Xie et al, 2021 ). The function of sRNAs can be analyzed by constructing transgenic plants using short tandem target mimic (STTM), CRISPR-Cas9, homologous recombination and other gene editing technologies ( Cui et al, 2020 ; Qiao et al, 2020 ; Ji et al, 2021 ). To better understand the function of sRNA and promote the use of sRNA in agricultural production, we reviewed the process of sRNA biogenesis, trafficking and the underlying mechanisms of its functions.…”

Roles of small RNAs in crop disease resistance

“…lycopersici (Fol), which is exported into tomato cells after infection and sequentially loaded onto tomato ARGONAUTE 4a (SlyAGO4a), targets the CBLinteracting protein kinase SlyFRG4. slyfrg4 mutant plants exhibit enhanced disease susceptibility to Fol, while slya-go4a knock-down plants display enhanced resistance to Fol (Ji et al 2021).…”

One microRNA‐like small RNA – two silencing pathways?

“…lycopersicum sRNA effector Fol-milR1 with antifungal defence in tomato (Solanum lycopersicum). The schematic is based on the findings by Ji et al (2021;10.1111/nph.17436) in the recently published article in New Phytologist. (a) Wild-type F. oxysporum f. sp.…”