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Title: BLADE-ON-PETIOLE1 and 2 Control Arabidopsis Lateral Organ Fate through Regulation of LOB-Domain and Adaxial-Abaxial Polarity Genes

item Fletcher, Jennifer

Submitted to: The Plant Cell
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/5/2007
Publication Date: 6/29/2007
Citation: Ha, C., Jun, J., Nam, H., Fletcher, J.C. 2007. BLADE-ON-PETIOLE1 and 2 Control Arabidopsis Lateral Organ Fate through Regulation of LOB Domain and Adaxial-Abaxial Polarity Fenes. The Plant Cell. 19:1809-1825.

Interpretive Summary: This article reports the molecular functions of two regulatory genes that are required for proper leaf formation during Arabidopsis development. We show that the BLADE-ON-PETIOLE1 (BOP1) and BOP2 genes act to induce the expression of three leaf fate-promoting target genes called LBD genes and repressing the expression of meristem fate-promoting target genes called class I knox genes. These regulatory interactions help newly forming leaf cells learn their identity. We also show that BOP1 and BOP2 play an important role in establishing the polarity of developing leaves, working to made the top (adaxial) side of the leaf different from the bottom (abaxial) side. Our findings demonstrate that BOP1 and BOP2 have critical functions in controlling two different aspects of Arabidopsis leaf development.

Technical Abstract: Continuous lateral organ formation is critical for higher plants to produce their characteristic architectures, but the regulatory pathways that specify organ cell fate are still poorly understood. Here, we report a novel function for BLADE-ON-PETIOLE1 (BOP1) and BOP2 in regulating Arabidopsis lateral organ cell fate and polarity, through the analysis of a loss-of-function mutants and transgenic plants that ectopically express BOP1 or BOP2. 35S:BOP1 and 35S:BOP2 plants exhibit a very short and compact stature, hyponastic leaves, and downward-orienting siliques. We show that the LATERAL ORGAN BOUNDARIES (LOB)-domain (LBD) genes ASYMMETRIC LEAVES2 (AS2) and LOB are up-regulated in 35S:BOP and down-regulated in bop mutant plants. Ectopic expression of BOP1 or BOP2 also results in repression of class I knox gene expression. We further demonstrate a role for BOP1 and BOP2 in the establishment of the adaxial-abaxial polarity axis in the leaf petiole, where they regulate PHB and FIL expression and overlap in function with AS1 and AS2. Interestingly, during this study we found that KANADI1 (KAN1) and KAN2 act to promote adaxial organ identity in addition to their well-known role in promoting abaxial organ identity. Our data indicate that BOP1 and BOP2 act in cells adjacent to the lateral organ boundary to repress genes that promote meristem cell fate and induce genes that promote lateral organ fate and polarity, thereby restricting the developmental potential of the organ-forming cells and facilitating their differentiation.