Magnaporthe oryzae effector MoSPAB1 directly activates rice Bsr-d1 expression to facilitate pathogenesis

Area of Science:

• Plant-pathogen interactions
• Molecular plant pathology
• Fungal genomics

Background:

• Fungal pathogens secrete effectors to suppress host immunity.
• Evidence for fungal effectors transactivating host defense-suppressing genes is scarce.
• Magnaporthe oryzae infection involves induction of rice Bsr-d1.

Purpose of the Study:

• To identify the fungal effector responsible for inducing rice Bsr-d1.
• To elucidate the mechanism of Bsr-d1 induction by fungal effectors.
• To investigate the conservation and function of related fungal effectors.

Main Methods:

• Yeast one-hybrid assays to detect DNA-binding activity.
• Electrophoretic mobility shift assays (EMSA) to confirm promoter binding.
• Site-directed mutagenesis to identify critical amino acids in MoSPAB1.
• Expression analysis in heterologous systems (kiwifruit and sorghum).

Main Results:

• The fungal effector MoSPAB1 directly binds to the Bsr-d1 promoter, inducing its expression.
• Amino acids 103-123 of MoSPAB1 are essential for Bsr-d1 promoter binding.
• MoSPAB1 and rice transcription factor MYBS1 compete for Bsr-d1 promoter binding.
• Homologous SPAB1 effectors in Colletotrichum species activate plant Bsr-d1 homologs, facilitating pathogenesis.

Conclusions:

• MoSPAB1 is a novel fungal effector that activates host gene expression to promote pathogenesis.
• The MoSPAB1-Bsr-d1 interaction represents a conserved mechanism across fungal pathogens.
• This conserved module offers potential targets for controlling fungal diseases in plants.