TheBLADE-ON-PETIOLE 1gene controls leaf pattern formation through the modulation of meristematic activity inArabidopsis

Abstract

The plant leaf provides an ideal system to study the mechanisms of organ formation and morphogenesis. The key factors that control leaf morphogenesis include the timing, location and extent of meristematic activity during cell division and differentiation. We identified an Arabidopsis mutant in which the regulation of meristematic activities in leaves was aberrant. The recessive mutant allele blade-on-petiole1-1 (bop1-1)produced ectopic, lobed blades along the adaxial side of petioles of the cotyledon and rosette leaves. The ectopic organ, which has some of the characteristics of rosette leaf blades with formation of trichomes in a dorsoventrally dependent manner, was generated by prolonged and clustered cell division in the mutant petioles. Ectopic, lobed blades were also formed on the proximal part of cauline leaves that lacked a petiole. Thus, BOP1regulates the meristematic activity of leaf cells in a proximodistally dependent manner. Manifestation of the phenotypes in the mutant leaves was dependent on the leaf position. Thus, BOP1 controls leaf morphogenesis through control of the ectopic meristematic activity but within the context of the leaf proximodistality, dorsoventrality and heteroblasty.BOP1 appears to regulate meristematic activity in organs other than leaves, since the mutation also causes some ectopic outgrowths on stem surfaces and at the base of floral organs. Three class I knox genes,i.e., KNAT1, KNAT2 and KNAT6, were expressed aberrantly in the leaves of the bop1-1 mutant. Furthermore, the bop1-1 mutation showed some synergistic effect in double mutants with as1-1 oras2-2 mutation that is known to be defective in the regulation of meristematic activity and class I knox gene expression in leaves. Thebop1-1 mutation also showed a synergistic effect with thestm-1 mutation, a strong mutant allele of a class I knoxgene, STM. We, thus, suggest that BOP1 promotes or maintains a developmentally determinate state in leaf cells through the regulation of class I knox genes.

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).…”

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

“…In Arabidopsis, the effect of the bop mutation (bop1 dominant negative mutation or bop1 bop2) was first described as outgrowth of the leaf blade on petioles (Ha et al, 2003(Ha et al, , 2004Hepworth et al, 2005;Norberg et al, 2005). Flower symmetry is also affected, with the formation of additional organs (Ha et al, 2003;Norberg et al, 2005;Xu et al, 2010).…”

“…Flower symmetry is also affected, with the formation of additional organs (Ha et al, 2003;Norberg et al, 2005;Xu et al, 2010). Thus, the phenotypes of the pea and Arabidopsis mutants are similar, affecting the development of the proximal region of the leaf as well as the symmetry of the flower.…”

BLADE-ON-PETIOLE–Dependent Signaling Controls Leaf and Floral Patterning in Arabidopsis

“…; Semiarti et al, 2001;Sun et al, 2002), AS2, which encodes a LOB domain/Leu zipper transcription factor (Iwakawa et al, 2002;Lin et al, 2003), and BLADE-ON-PETIOLE1 (BOP1), recently shown to encode a NONEXPRESSOR OF PR GENES1 (NPR1)-like transcription factor (Ha et al, 2003(Ha et al, , 2004. AS1 and AS2 function in the same genetic pathway and bind to each other in yeast, suggesting that they are members of a complex (Byrne et al, 2002;Iwakawa et al, 2002;Lin et al, 2003;Xu et al, 2003).…”

“…AS1 and AS2 function in the same genetic pathway and bind to each other in yeast, suggesting that they are members of a complex (Byrne et al, 2002;Iwakawa et al, 2002;Lin et al, 2003;Xu et al, 2003). Analysis of double mutants shows that BOP1 has a synergistic genetic relationship with AS1 and AS2 (Ha et al, 2003), indicating that AS1/AS2 and BOP1 might function in separate genetic pathways controlling proximal-distal patterning. A common feature of each mutant, however, is the misexpression of meristempromoting class 1 knotted1-like homeobox (knox) genes in leaf tissue, indicating that exclusion of knox gene expression and/or repression of meristematic activity might be an important determinant of proximal-distal patterning (Byrne et al, 2000;Ori et al, 2000;Semiarti et al, 2001;Ha et al, 2003).…”