P-098 - TOPLESS1 is required for Fusarium oxysporum effector SIX8-triggered immunity in Solanum americanum

Fusarium oxysporum f.sp. lycopersici (Fol) is a soilborne pathogen responsible for tomato wilt disease, causing significant crop losses. During infection, Fol secretes small effector proteins called Secreted in Xylem (SIX), which manipulate the host immune system and facilitate pathogen colonization. In resistant plants, resistance (R) proteins recognize these effectors, triggering a hypersensitive response (HR) to limit pathogen spread. In the Fusarium–tomato interaction, only a few R proteins—namely I, I-2, and I-3—are known to recognize specific SIX effectors. In this study, we aimed to identify additional R proteins recognizing SIX effectors by screening natural Solanum americanum accessions using transient agroinfiltration. Our results show that agroinfiltration with SIX8 induced a strong HR in a resistant S. americanum accession, suggesting a novel R protein specific to SIX8. We also observed that 12 out of 13 natural variants of SIX8 induced robust HR despite amino acid polymorphisms. Additionally, we identified six TOPLESS (TPL) homologs in S. americanum, and yeast two-hybrid assays revealed that SIX8 interacts with two homologs, SaTPL1 and SaTPL2. VIGS experiments showed that silencing SaTPL1, but not SaTPL2, abolished the SIX8-induced HR, highlighting SaTPL1's critical role in the HR and resistance response. Our study provides insights into SIX8 recognition and could aid in developing Fusarium wilt-resistant crops in the future.