The conserved guanyl-specific ribonuclease T1 effector EC19 is required for full virulence of the vascular Fusarium fungus in tomato

Here, we identify EC19, a secreted effector from <i>Fusarium oxysporum</i> f. sp. <i>lycopersici</i> (Fol), as a key virulence factor in tomato wilt disease. In-locus knockout of <b>EC19</b> significantly reduces Fol virulence, whereas genetic complementation restores pathogenicity. EC19 encodes a conserved ribonuclease T1–like protein with single-stranded RNA cleavage activity and is specifically induced during Fol infection. Structural prediction indicates that EC19 shares high structural similarity with RNase T1 (2RNT). Transient expression assays show that EC19 predominantly localizes to the plant nucleus. Moreover, tomato plants overexpressing EC19 display enhanced susceptibility to Fol, accompanied by suppressed expression of SA-, JA-, ET-, and ABA-associated defense genes. These results demonstrate that EC19 promotes Fol virulence by targeting host RNA metabolism and attenuating hormone-mediated immune responses.