BLADE-ON-PETIOLE1and2ControlArabidopsisLateral Organ Fate through Regulation of LOB Domain and Adaxial-Abaxial Polarity Genes

Abstract

We report a novel function for BLADE-ON-PETIOLE1 (BOP1) and BOP2 in regulating Arabidopsis thaliana lateral organ cell fate and polarity, through the analysis of 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 downwardorienting siliques. We show that the LATERAL ORGAN BOUNDARIES (LOB) domain genes ASYMMETRIC LEAVES2 (AS2) and LOB are upregulated in 35S:BOP and downregulated 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 establishing 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 confer 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.

The Barley Uniculme4 Gene Encodes a BLADE-ON-PETIOLE-Like Protein That Controls Tillering and Leaf Patterning

“…S4) reveal that the BOP1 and BOP2 genes of Arabidopsis, which mutually share 80% identity at the amino acid level, as well as the soybean (Glycine max) Glyma03g28440 and Glyma19g31180 genes (82% amino acid identity), both derive from independent, recent lineage-specific gene duplications within the dicots. This is consistent with the observed high degree of redundancy of Arabidopsis BOP genes at both the functional and expression pattern levels (Norberg et al, 2005;Ha et al, 2007;Xu et al, 2010). By way of contrast, Cul4 and MLOC_61451.6 share 58% amino acid identity and, as for BOP paralogs in other monocot species, fall into distinct, highly supported clades deriving from a more ancient duplication.…”

“…Arabidopsis bop1 bop2 double mutants are characterized by the ectopic outgrowth of blade tissue on the petiole (Ha et al, 2003(Ha et al, , 2004(Ha et al, , 2007Hepworth et al, 2005). Morphological alterations of the stipules located at the base of the leaf were also observed in loss-of-function mutants of BOP orthologs in pea and M. truncatula (Couzigou et al, 2012).…”

NODULE ROOT and COCHLEATA Maintain Nodule Development and Are Legume Orthologs of Arabidopsis BLADE-ON-PETIOLE Genes

“…To test whether NOOT is a functional ortholog of BOP1 and 2, we overexpressed NOOT, or a NOOT:GFP translational fusion, in Arabidopsis. The two constructs phenocopy BOP overexpression in Arabidopsis (see Supplemental Figures 7A to 7D online), as previously observed by Ha et al (2007) and Norberg et al (2005), demonstrating that NOOT and BOP are functional orthologs. In addition, the NOOT:GFP fusion is targeted to the nucleus, indicating that the NOOT protein is a nuclear protein (see Supplemental Figures 7E and 7F online).…”

Transcriptomic Analyses Indicate That Maize Ligule Development Recapitulates Gene Expression Patterns That Occur during Lateral Organ Initiation

“…Arabidopsis BOP genes function in leaf proximal-distal patterning (Ha et al, 2003(Ha et al, , 2004(Ha et al, , 2007, and our results suggest that this role is conserved in maize. In situ hybridization of the maize BOP-like gene reveals transcript accumulation at organ boundaries, the base of leaf primordia (presheath domain), in axillary meristems, and in developing ligules ( Figures 5M to 5P).…”