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Title: BLADE-ON-PETIOLE1 coordinates organ determinacy and axial polarity in Arabidopsis by directly activating ASYMMETRIC LEAVES2

Author
item JUN, JIHYUNG - University Of California
item HA, CHAN MAN - University Of California
item Fletcher, Jennifer

Submitted to: The Plant Cell
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2009
Publication Date: 1/29/2010
Citation: Jun, J., Ha, C., Fletcher, J.C. 2010. BLADE-ON-PETIOLE1 coordinates organ determinacy and axial polarity in Arabidopsis by directly activating ASYMMETRIC LEAVES2. The Plant Cell. 22:62-76.

Interpretive Summary: This article reports the molecular function for the BLADE-ON-PETIOLE1 (BOP1) and BOP2 genes that regulate Arabidopsis leaf patterning and growth. We show that BOP1 and BOP2 act to turn on the expression of specific downstream target genes, which is critical for cells to assume their appropriate fate as basal leaf cells. We demonstrate that BOP1 and BOP2 directly activate the expression of the ASYMMETRIC LEAVES2 gene by binding to sites in its promoter. We also find that repression of BOP1 and BOP2 activity in stem cells is necessary to establish the embryo shoot apex. Our work reveals that BOP1 and BOP2 play important roles in promoting basal leaf cell fate during leaf formation and patterning.

Technical Abstract: Continuous organ formation is a hallmark of plant development that requires organ-specific gene activity to establish determinacy and axial patterning, yet the molecular mechanisms that coordinate these events remain poorly understood. Here, we show that the organ-specific BTB-POZ domain proteins BLADE-ON-PETIOLE1 (BOP1) and BOP2 function as transcriptional activators during Arabidopsis thaliana leaf formation. We identify as a direct target of BOP1 induction the ASYMMETRIC LEAVES2 (AS2) gene, which promotes leaf cell fate specification and adaxial polarity. We find that BOP1 associates with the AS2 promoter and that BOP1 and BOP2 are required for AS2 activation specifically in the proximal, adaxial region of the leaf, demonstrating a role for the BOP proteins as proximal-distal as well as adaxial-abaxial patterning determinants. Furthermore, repression of BOP1 and BOP2 expression by the indeterminacy-promoting KNOX gene SHOOTMERISTEMLESS is critical to establish a functional embryonic shoot apical meristem. Our data indicate that direct activation of AS2 transcription by BOP1 and BOP2 is vital for generating the conditions for KNOX repression at the leaf base and may represent a conserved mechanism for coordinating leaf morphogenesis with patterning along the adaxial-abaxial and the proximal-distal axes.