The BLADE-ON-PETIOLE 1 gene controls leaf pattern formation through the modulation of meristematic activity in Arabidopsis.
2003
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, BOP1
regulates 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 or
as2-2 mutation that is known to be defective in the regulation of
meristematic activity and class I knox gene expression in leaves. The
bop1-1 mutation also showed a synergistic effect with the
stm-1 mutation, a strong mutant allele of a class I knox
gene, STM . We, thus, suggest that BOP1 promotes or maintains
a developmentally determinate state in leaf cells through the regulation of
class I knox genes.
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