Plant Molecular Biology 49: 567–577, 2002.
© 2002 Kluwer Academic Publishers. Printed in the Netherlands.
Apple has two orthologues of FLORICAULA/LEAFY involved in ﬂowering
, Qiu-fen Cao
, Nobuhiro Kotoda
, Jun-ichi Soejima
and Tetsuo Masuda
Apple Research Center, National Institute of Fruit Tree Science, Shimokuriyagawa, Morioka, Iwate 020-0123
author for correspondence; e-mail: email@example.com);
Faculty of Agriculture, Iwate University,
Morioka, Iwate 020-8550, Japan.
Received 20 March 2001; accepted in revised form 28 November 2001
Key words: AFL1, AFL2, apple, ﬂoral meristem identity gene, FLORICAULA/LEAFY
Two orthologues of FLORICAULA/LEAFY, AFL1 and AFL2 (apple FLO/LFY), were isolated from the ﬂoral buds
of apple trees. Their expression was detected in various tissues and during differentiation of the ﬂoral buds.
Furthermore, the ﬂowering effectiveness of each gene was assessed with transgenic Arabidopsis.BothAFL1 and
AFL2 showed high homology to each other (90%) and a high degree of similarity to PTLF and PEAFLO (70%),
which are homologues of FLO/LFY from poplar and pea, respectively. RNA blot analysis showed that AFL1 was
expressed only in the ﬂoral bud during the transition from vegetative to reproductive growth, whereas AFL2 was
expressed in vegetative shoot apex, ﬂoral buds, ﬂoral organs and root. Genomic Southern analysis showed that
apple had other homologues in addition to AFL1 and AFL2. The transgenic Arabidopsis with over-expressed AFL2
showed accelerated ﬂowering and gave rise to several solitary ﬂowers from rosette axils directly. AFL1 had similar
effects, but the phenotypes of the transgenic Arabidopsis with AFL1 were weaker than those with AFL2.These
results suggest that both genes are involved in ﬂower differentiation in apple.
Increasing knowledge of the ﬂowering mechanism in
Arabidopsis has opened the ﬂoodgate for the identiﬁ-
cation of several key genes that control ﬂoral devel-
opment (Okamuro et al., 1993; Levy and Dean 1998;
Pidkowich et al., 1999). One of such genes, LEAFY
(LFY), has been reported to be necessary for the tran-
sition from vegetative to reproductive development. It
has been deﬁned as a ﬂoral meristem identity gene like
FLORICAULA (FLO) from Antirrhinum majus (Coen
et al., 1990). Mutations in these genes result in the
conversion of ﬂowers into indeterminate secondary
shoots (Weigel et al., 1992). The over-expression of
LFY under the 35S promoter in Arabidopsis caused
early ﬂowering and converted all lateral shoots info
solitary ﬂowers. In heterologous plants such as as-
pen, LFY could have effects similar to acceleration
The nucleotide/amino acid sequence data reported will appear in the
EMBL, GenBank and DDBJ databases under the accession numbers
AB056158 (AFL1) and AB056159 (AFL2).
of ﬂowering and induction of ectopic ﬂowers (Weigel
and Nilsson 1995). These reports strongly suggest that
the ability to control the expression of LFY,orofor-
thologues from other plants, could make it possible to
induce various plants to blossom whenever and how-
ever possible. Consequently, these studies should be
considered a contribution to agriculture and forestry.
Apple is one of the most commercially valuable
fruit trees, with production second only to grape in the
whole world. Apple has an extended juvenile phase,
during which vegetative growth is maintained. This
characteristic is recognized as a disadvantage in breed-
ing and in stable annual production. Thus, it will
be necessary to understand the genetic mechanism
underlying transition from vegetative to reproductive
phase. Only a few studies have reported on the mech-
anism underlying the development of apple ﬂowers.
Recently, MADS-box genes have been correlated to
apple fruit set, and they have been cloned and charac-
terized (Sung et al., 1999, 2000). These apple MADS
genes seem to be involved in ﬂoral organ and fruit