Plant Molecular Biology 44: 107–122, 2000.
© 2000 Kluwer Academic Publishers. Printed in the Netherlands.
Characterization of a gene from Zea mays related to the Arabidopsis
ﬂowering-time gene LUMINIDEPENDENS
Steven van Nocker
, Michael Muszynski
, Kristin Briggs
and Richard M. Amasino
Department of Horticulture, Michigan State University, 390 Plant and Soil Science Building, East Lansing, MI
48824, USA (
author for correspondence; e-mail: firstname.lastname@example.org);
Pioneer Hi-Bred International, Inc.,
7300 NW 62nd Ave., Johnston, IA 50131-1004, USA;
Department of Biochemistry, University of Wisconsin-
Madison, Madison, WI 53706, USA;
Present address: Epicyte Pharmaceutical Inc., 5810 Nancy Ridge Drive,
Suite 150, San Diego, CA 92121, USA
Received 25 January 2000; accepted in revised form 26 May 2000
Key words: FLOWERING LOCUS C (FLC), ﬂowering time, homeodomain, LUMINIDEPENDENS (LD),
meristem, SHOOTMERISTEMLESS (STM)
The molecular biology of ﬂowering has been most extensively studied in the quantitative long-day plant Ara-
bidopsis thaliana.TheArabidopsis LUMINIDEPENDENS (LD) gene encodes a potential transcriptional regulator
that acts as a positive effector of ﬂowering, at least in part through suppression of the ﬂoral inhibitor gene FLC.
As an initial step to explore the conservation of the molecular mechanisms of ﬂowering among plants of various
ﬂowering habits, and to further investigate the molecular action(s) of LD, we have identiﬁed a gene from maize (Zea
mays) that is closely related to Arabidopsis LD. The major product of this gene, which we have designated ZmLD
for Zea mays LUMINIDEPENDENS, contains four conserved regions that may constitute functionally important
components of the LD proteins. One of these regions closely resembles the canonical homeodomain. The ZmLD
gene exists as a single copy in the maize genome, and generates a major ca. 4.0 kb transcript, and a minor ca.
2.6 kb transcript that results from alternative transcriptional termination. The 4.0 kb ZmLDα transcript accumulated
to highest levels in proliferative tissues, including the shoot apex and developing inﬂorescences. Expression of
ZmLDα under control of the Arabidopsis LD promoter in transgenic Arabidopsis caused developmental defects
similar to those conferred by loss-of-function mutations in a class of genes involved in maintaining the proliferative
nature of the shoot, inﬂorescence, and ﬂoral meristems. These effects were not inﬂuenced markedly by the activities
of the Arabidopsis LD or FLC genes. We consider the implications for the conservation of LD function between
maize and Arabidopsis.
The timing of ﬂowering in seed plants is determined
by an innate developmental program that is often
strongly inﬂuenced by environmental cues such as
photoperiod and temperature. Perception of environ-
mental factors allows plants to sense their progression
through the seasons and initiate ﬂowering and subse-
quent seed production at the optimum time to max-
imize reproduction; for self-incompatible plants, the
coordination of ﬂowering also increases the likelihood
of successful pollination. Diversiﬁcation in sensing
and/or response to these environmental inﬂuences has
allowed various genotypes to establish and maintain
speciﬁc ecological niches.
The genetics and molecular biology of the devel-
opmental transition from vegetative to reproductive
growth have been most extensively studied in Ara-
bidopsis thaliana, a member of the mustard family
that exhibits a quantitative long-day ﬂowering habit
and exists in both annual and winter-annual forms.
In this species, genetic analyses have revealed many
genes that are directly involved in the positive or nega-
tive regulation of ﬂowering (for review, see Koornneef