Biology Reference
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control the expression of TOC1 in the clock core. This contrasts with other spe-
cies, like Populus, where duplications of the LHY/CCA1 genes contribute to an
apparently more complex mode of clock control [68].
Vernalization pathway in Arabidopsis culminates in FLC and FLC-like floral
repressors [13,50]. They have been functionally characterized only in Brassicaceae
[13,69], although homologous MADS box genes have been recently found from
several eudicot lineages by phylogenetic analysis [51]. However, we were not able
to identify FLC-like sequences in Rosaceae by using several FLC-like sequences
as a query. Similarly, also FRI homologs were lacking from the Rosaceae sequence
collections. However, putative homologs of FRI-like genes, FRL1 and FRL2,
which are involved in FLC activation in Arabidopsis [15] were found, as well as
several other homologs of genes belonging to FLC regulating protein complexes.
Despite the presence of these transcripts, the presence of FLC is unclear, since at
least PRC2 complex has several target genes [70]. Cloning and characterization
of putative FLC-like and FRI genes as well as FT in strawberry would greatly
expand our understanding of strawberry flowering pathways, and therefore, it
is one of the most important targets of further studies. If these transcripts are
present in strawberry, it is likely that the precise control of flowering has placed
their expression in specific tissues or contexts where they are not easily detected.
However, their presence should be substantiated in analysis of the impending ge-
nome sequence. Another important goal is the identification of putative Rosaceae
or Fragaria specific flowering time genes. Ultimately, transcriptomics studies and
functional analysis of central genes may reveal how different flowering pathways,
which may be closely related to Arabidopsis pathways, make seasonal flowering
in strawberry.
What is the SFL Gene?
SFL is a single dominant locus that enforces seasonal flowering habit in wild
strawberry, and homozygous mutation in this locus leads to continuous flowering
habit in at least one genotype, 'Baron Solemacher' [36]. In SD genotypes of wild
strawberry, SD or low temperature induce flowering [27] probably by overcoming
the function of SFL repressor gene. We showed here that EB genotypes 'Baron
Solemacher' and 'Hawaii-4' produce only 5 - 6 leaves to the main crown before
the formation of the terminal inflorescence in LD at 18°C. Hence, flowering in-
duction in these conditions occurs soon after germination. In SD (12 h) or at low
temperature (11°C) instead, plants formed several leaves more before the inflo-
rescence. This finding shows that, in contrast to SD genotypes, both SD and low
temperature restrain flowering induction in these genotypes, confirming earlier
suggestions that EB genotypes of wild strawberry are in fact LD plants [35]. Most
