Fungal effector‐based strategies for sustainable rice disease control: Transgenic expression and engineered biocontrol approaches deliver broad‐spectrum resistance

Rice is one of the most important food crops in the world and it is prone to attack by many diseases, such as the rice blast, sheath blight, bacterial leaf blight, and so on. These diseases represent the main constraints in rice production, threatening food security and safety. Here, new control strategies against these major rice diseases have been developed either by heterologous expression of a pathogen effector UvScd1 from false smut fungus Ustilaginoidea virens or by spraying the engineered biocontrol agent Bacillus subtilis secreting the effector UvScd1. Compared to the wild-type rice Zhonghua11 (ZH11), the rice line heterologously expressing UvScd1 showed lesion mimics and upregulated the expression of defense-related genes in leaves, including genes related to the JA and SA signaling pathways. As expected, the transgenic rice line showed broad-spectrum resistance to hemibiotrophic fungus Magnaporthe oryzae, necrotrophic fungus Rhizoctonia solani, and bacterium Xanthomonas oryzae pv. oryzae (Xoo), while there was no effect on yield-related agronomic traits compared with ZH11, suggesting that the effector UvScd1 confers both plant resistance via induction of ROS and defense-related genes, and maintains the balance between plant resistance and yield. In field experiments, comparable control efficiencies against these major rice diseases were achieved by spraying B. subtilis engineered to secrete UvScd1 and corresponding chemical pesticides, underscoring that use of biocontrol agents to secrete certain pathogen effector proteins is an effective strategy for the management of plant diseases. It is noteworthy that the application of B. subtilis engineered to secrete UvScd1 also achieved effective control for a variety of crop diseases, suggesting its excellent potential for use in practice.