Investigating the Roles of BLADE-ON-PETIOLE1 and 2 with Clade I TGACG-Motif Binding Basic Leucine Zipper Transcription Factors in the Regulation of Development and Defense in Arabidopsis thaliana

Plant health relies on a critical balance between growth and defense. The activation of defense responses is generally linked to growth repression but the mechanisms behind this response are unclear. BTB-ankyrin domain-containing proteins comprise a family of transcriptional co-regulators in land plants with roles in development and defense. Discovered in Arabidopsis thaliana, proteins in this family form two groups: NONEXPRESSOR OF PATHOGENESIS RELATED GENES 1 (NPR1) and related proteins are essential for systemic acquired resistance to pathogens whereas BLADE-ON-PETIOLE 1 and 2 proteins regulate plant morphology. Structurally, proteins from both groups lack a DNA-binding domain but share conserved protein-interacting BTB/POZ and ankyrin domains. BTB-ankyrin proteins interact with TGACG-motif binding (TGA) basic leucine zipper (bZIP) and WRKY transcription factors but functional knowledge of these interactions is incomplete. My thesis explores roles for BOP1 and BOP2 in development and defense with TGA bZIP transcription factors as functional partners. First, I showed that clade I TGAs function in the same genetic pathways as BOP1/2 important for the development of organ boundaries and plant architecture. Second, I showed that BOP1/2 function in pattern-triggered immunity through interaction with clade I TGA and WRKY transcription factors. Lastly, I found that BOP1/2 regulate plant defense in an NPR1-independent manner. Collectively, these findings revealed a dual role of BOP1/2 in plant development and defense.