Plants have evolved a diversity of inflorescence architectures and variations in flowering time to maximize reproductive success within their environment. BLADE-ON-PETIOLE 1, 2 (BOP1/2) are a class of BTB-ankryin transcription factors. BOP activity is concentrated at meristem-organ junctions (“lateral organ boundaries”) where it functions to control the morphology of leaves, flowers, fruits, and inflorescences.
Gain-of-function BOP1/2 plants mimic loss-of-function in KNOX and BELL three-amino-acid-loop extension (TALE) homeodomain proteins. BEL1-like (BELL) genes PENNYWISE (PNY) and
POUNDFOOLISH (PNF) are required for Arabidopsis thaliana competence to flower, whereas the KNOTTED1-like HOMEOBOX (KNOX) gene BREVIPEDICELLUS (BP) in conjunction with PNY control internode elongation and stem patterning in inflorescences. In this thesis, I used BOP gain-of-function as an approach to uncover interactions with TALE homeobox genes in regulation of flowering and inflorescence architecture.
Firstly, I showed that BP/PNY in stems and PNY/PNF in meristems restrict BOP1/2 expression to boundaries to promote flowering, internode elongation and vascular patterning. Secondly, I identified lateral organ boundary genes KNOTTED-like from ARABIDOPSIS THALIANA6 (KNAT6) and ARABIDOPSIS THALIANA HOMEBOX GENE1 (ATH1) as required by BOP1/2 to antagonize BP/PNY activity through reciprocal regulation of downstream target genes, including biosynthetic enzymes required for lignin deposition in stems. Lastly, BOP1/2 lack a DNA-binding domain and associate with promoter DNA by binding to TGACG (TGA) bZIP transcription factors. I identified TGA1 and TGA4 bZIP factors required by BOP1/2 to exert changes in flowering and inflorescence architecture.
Collectively, these findings shed light on how interplay between BOP1/2 and KNOX-BELL complexes in the meristem and lateral organ boundaries governs flowering and inflorescence architecture in a model plant species.