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Roles of the BLADE-ON-PETIOLE genes in Arabidopsis thaliana lateral organ development McKim, Sarah Michelle

Abstract

The BLADE-ON-PETIOLE1 (BOP1) and BOP2 genes encode redundant transcription factors involved in morphological patterning in the proximal regions of lateral organs in Arabidopsis thaliana. Loss-of-function bop1 bop2 mutants display several developmental defects including a loss of floral organ abscission. Abscission occurs along specialised cell files, called abscission zones (AZs), which form at the boundary between the leaving organ and main plant body. This dissertation examined the contribution of BOP1 and BOP2 to the known abscission developmental framework and determined that bop1 bop2 flowers lack anatomy associated with AZs. Vestigial cauline leaf AZs are also absent in bop1 bop2 suggesting that BOP proteins are essential to establish AZ anatomy in both leaves and flowers, the first genes identified in Arabidopsis to do so. In support of this hypothesis, BOP1/2 activity is required for both premature floral organ abscission and ectopic cauline leaf abscission promoted by the constitutive expression of INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) gene. In addition, BOP1 and BOP2 were found to promote growth of nectary glands which normally develop off the receptacle at the base of stamens adjacent to AZs. Boundary, nectary and AZ specific-gene expression is relatively unperturbed in bop1 bop2, indicating that positional information is intact. Taken together, these data suggest that BOP1 and BOP2 are key downstream modulators of positional programs operating at the lateral organ-plant body interface. bop1 bop2 flowers also show a subtle loss in floral meristem identity. Genetic analyses revealed a crucial role for BOP1 and BOP2 in suppression of secondary inflorescence identity in early floral primordia only when functions either LEAFY (LFY) or APETALA (AP1) were compromised, suggesting that BOP1 and BOP2 are potentiators of LFY and AP1 function rather than floral meristem identity genes themselves. BOP1 and BOP2 belong to the NPR1-like protein family. A phylogenetic analysis in land plants found both monocot and dicot BOP protein homologues that cluster independently from other NPR1-like proteins. A final contribution examined the subcellular localisation of BOP2 during development and showed that BOP protein-protein interactions in planta showed behaviour consistent with that known for NPR1.

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