An early auxin-induced gene was isolated from rice (Oryza sativa
L. subsp. japonica cv Nihonmasari) coleoptiles by a
fluorescent-labeled differential display screen. The full-length
gene contains conserved domains characteristic for the
cytochrome P450 superfamily. This gene, designated as CYP87A3,
was weakly expressed in dark-grown coleoptiles but was
up-regulated rapidly and transiently when coleoptile segments
were incubated in 5 m indole-3-acetic acid. This induction
by auxin could not be suppressed by cycloheximide. Depletion of
segments from endogenous auxin reduced the amount of CYP87A3
transcripts. The CYP87A3 transcript level was rapidly, although
transiently, up-regulated in response to light as well. The
observed pattern of gene regulation might indicate a role in the
suppression of auxin-induced coleoptile growth.
The role of CYP87A3 is discussed with respect to auxin signaling
in the regulation of coleoptile growth.