Biology Reference
In-Depth Information
(Fragaria × ananassa Duch.) and wild strawberry (F. vesca L.) are Junebear-
ing SD plants, which are induced to flowering in decreasing photoperiod in
autumn [26,27]. In some genotypes, flowering induction is also promoted
by decreasing temperatures that may override the effect of the photoperiod
[27,28]. In contrast to promotion of flowering by decreasing photoperiod
and temperature, these “autumn signals” have opposite effect on vegetative
growth. Petiole elongation decreases after a few days, and later, around the
floral transition, runner initiation ceases and branch crowns are formed from
the axillary buds of the crown [29,30]. Crown branching has a strong effect
on cropping potential as it provides meristems that are able to initiate inflo-
rescences [31].
In addition to SD plants, everbearing (EB) genotypes are found in garden
strawberry and in wild strawberry [29,32]. Environmental regulation of induc-
tion of flowering in EB genotypes has been a topic of debate for a long time.
Several authors have reported that these genotypes are day-neutral [29,33]. Re-
cent findings, however, show that long-day (LD) accelerates flowering in several
EB Fragaria genotypes [34,35]. Interestingly, in wild strawberry genotype 'Baron
Solemacher' recessive alleles of SFL gene locus (SEASONAL FLOWERING
LOCUS) have been shown to cause EB flowering habit [36]. SFL has not been
cloned, but it seems to encode a central repressor of flowering in wild strawberry.
Consistent with the repressor theory, LD grown strawberries have been shown to
produce a mobile floral inhibitor that is able to move from mother plant to the
attached runner plant [37]. GA is one candidate corresponding to this inhibitor,
since exogenously applied GA has been shown to repress flowering in strawberries
[38,39].
Identification of central genes regulating flowering time and EB flowering
habit, as well as those controlling other processes affecting flowering, is an
important goal that would greatly accelerate breeding of strawberry and other
soft fruit and fruit species of Rosaceae family. In this paper, we have searched
Fragaria homologs with the known Arabidopsis flowering time genes by EST
sequencing and bioinformatics analysis. Dozens of putative flowering genes
corresponding to all known genetic pathways regulating flowering time were
identified. The expression analysis of several candidate flowering time genes
revealed only few differences between the SD and EB wild strawberries, in-
cluding the presence or absence of AP1 mRNA in the apices of EB and SD
genotypes, respectively. Our data provides groundwork for detailed studies of
flowering time control in Fragaria using transcriptomics, functional genomics
and QTL mapping.
