Table_1_The Flower-Infecting Fungus Ustilaginoidea virens Subverts Plant Immunity by Secreting a Chitin-Binding Protein.XLSX

Ustilaginoidea virens is a biotrophic fungal pathogen specifically colonizing rice floral organ and causes false smut disease of rice. This disease has emerged as a serious problem that hinders the application of high-yield rice cultivars, by reducing grain yield and quality as well as introducing mycotoxins. However, the pathogenic mechanisms of U. virens are still enigmatic. Here we demonstrate that U. virens employs a secreted protein UvCBP1 to manipulate plant immunity. In planta expression of UvCBP1 led to compromised chitin-induced defense responses in Arabidopsis and rice, including burst of reactive oxygen species (ROS), callose deposition, and expression of defense-related genes. In vitro-purified UvCBP1 protein competes with rice chitin receptor OsCEBiP to bind to free chitin, thus impairing chitin-triggered rice immunity. Moreover, UvCBP1 could significantly promote infection of U. virens in rice flowers. Our results uncover a mechanism of a floral fungus suppressing plant immunity and pinpoint a universal role of chitin-battlefield during plant–fungi interactions.

稻曲病菌（Ustilaginoidea virens）是一类专性寄生水稻花器官的活体营养型真菌病原菌，可引发水稻稻曲病。该病害现已成为制约高产水稻品种推广应用的严重问题，不仅降低籽粒产量与品质，还会产生真菌毒素。然而，目前人们对稻曲病菌的致病机制仍不甚明晰。本研究证实，稻曲病菌可通过分泌蛋白UvCBP1操控植物免疫。在植物体内表达UvCBP1，会削弱拟南芥和水稻的几丁质诱导防御反应，包括活性氧（ROS）爆发、胼胝质沉积以及防御相关基因的表达。体外纯化的UvCBP1蛋白可与水稻几丁质受体OsCEBiP竞争结合游离几丁质，从而阻断几丁质触发的水稻免疫反应。此外，UvCBP1可显著促进稻曲病菌在水稻花器官中的侵染过程。本研究揭示了一类花部真菌抑制植物免疫的分子机制，并明确了几丁质在植物-真菌互作中的核心战场功能。