The GT1-WRKY53-BZR1 module regulates blast resistance and grain size in rice

Developing disease-resistant rice varieties is a crucial strategy for effective disease management. Both high yield and strong disease resistance are essential targeting traits in rice breeding, yet the signaling pathways governing these traits often exhibit antagonistic interactions. In this study, grassy tiller 1 ( GT1 ) was identified as a positive regulator of rice blast resistance. Overexpression of GT1 enhanced grain size, whereas GT1 mutants exhibited normal grain size. Further analysis revealed that GT1 interacts with BZR1 and WRKY53, two key transcription factors in the brassinosteroid (BR) signaling pathway, both of which positively regulate rice blast resistance. Transcriptome analysis of GT1 overexpressing ( GT1 OX ), bzr1-D , and WRKY53 overexpressing ( WRKY53 OX ) plants identified WRKY45 , a master regulator of rice blast resistance, as a potential downstream target of the GT1-WRKY53-BZR1 module. Yeast one-hybrid, transient expression, and chromatin immunoprecipitation assays demonstrated that GT1 and BZR1 directly activate WRKY45 by binding to its promoter, while WRKY53 does not directly bind to WRKY45 but may enhance its expression through complex formation. The genetic combination of WRKY53 OX and bzr1-D indicated an additive effect of BZR1 and WRKY53 on blast resistance. Additionally, WRKY53 OX and GT1 OX , but not bzr1-D , promoted grain enlargement. Further analysis of downstream genes identified the BR receptor BRASSINOSTEROID INSENSITIVE1 ( BRI1 ) as a positively regulated target of GT1 and WRKY53, which in turn enhances grain size. These findings demonstrate that GT1 interacts with BR signaling transcription factors to regulate both rice blast resistance and grain size by activating WRKY45 and BRI1 .