Fig. 2

Schematic representation showing the molecular mechanisms by which Ustilaginoidea virens effectors target host proteins and suppress plant immunity. Chitin is recognized by OsCEBiP and OsCERK1, thereby promoting the phosphorylation of SnRK1A and OsMPK6. UvCBP1 is a multifunctional protein. The effector blocks chitin access to the receptor OsCEBiP and disarms chitin-triggered immunity. Meanwhile, UvCBP1 interacts with the rice scaffold protein OsRACK1A and competes for its interaction with the NADPH oxidase OsRBOHB, thus inhibiting ROS accumulation. Activated SnRK1A phosphorylates XB24 and promotes ATPase activity to degrade ATP. SCRE1 outcompetes SnRK1A and ATP for XB24 binding, thus inhibiting ATPase activity and rice immunity. As a negative immune regulator, activated OsMPK6 is prone to 26S proteasome-mediated degradation. SCRE6 functions as a tyrosine phosphatase that dephosphorylates and stabilizes OsMPK6. UvPr1a, as a serine protease subtilase, directly degrades OsSGT1, a positive immune regulator. In the nuclei, SCRE4 inhibits the expression of OsARF17, encoding a positive immune regulator. UvSec117 recruits OsHDA701 into the nucleus and enhances its deacetylation activity. OsHDA701-mediated deacetylation of histone H3K9 inhibits the activation of defense genes and rice immunity. UvHrip1 interacts with OsHGW in nuclei and inhibits plant immunity via an unknown mechanism. Interestingly, SGP1 is recognized as a PAMP in the leaves, while the effector contributes to panicle infection. Collectively, distinct effectors promote U. virens infection through various molecular mechanisms. Green boxes indicate U. virens effectors; red boxes indicate positive immune regulators; purple boxes indicate negative immune regulators. PR, Pathogenesis-related; ROS, Reactive oxygen species; ATP, Adenosine triphosphate; ADP, Adenosine diphosphate; Ac, Adenylate cyclase; P, Phosphorus. SGP1, SUPPRESSOR OF G2 ALLELE OF SKP1; SCRE, Small cysteine-rich effector. Created with BioRender (www. BioRender.com)