Identification of candidate RXLR effectors from downy mildew of foxtail millet pathogen Sclerospora graminicola and functional analysis of SG_RXLR41

Abstract Downy mildew caused by Sclerospora graminicola is a systemic disease that affects the yield and quality of foxtail millet. This obligate biotrophic oomycete manipulates host physiology and immune processes through numerous effectors. A thorough comprehension of effector biology is crucial to unravel disease mechanisms and understand host plant resistance. In this study, bioinformatic analyses revealed 498 potentially secreted proteins in S . graminicola , of which 62 were identified as RXLR effectors; 46 RXLR‐encoding genes exhibited upregulated expression during the early stages of infection. To elucidate the functions of these secreted proteins, a heterogeneous expression system was developed using Nicotiana benthamiana . Twenty‐one RXLR effectors secreted by S . graminicola were transiently expressed in N . benthamiana , of which four could suppress INF1‐triggered cell death. Various defence responses in N . benthamiana were attenuated, including inhibition of defence gene expression, reduction of reactive oxygen species (ROS) accumulation and diminished callose deposition. The expression of SG_RXLR41 also enhanced the growth of Phytophthora capsici on N . benthamiana leaves. These findings indicate that S . graminicola facilitates infection and expansion through the secretion of multiple RXLR effectors, and SG_RXLR41 is an important virulence‐related effector that is involved in manipulating plant immunity by suppressing cell death.