Biology Reference
In-Depth Information
generative reproduction, and the same developmental program is repeated from
year to year. Regulation of generative development in these species is even more
complex, because other processes like juvenility, winter dormancy and chilling are
tightly linked to the control of flowering time.
In Arabidopsis photoperiodic flowering pathway, phytochrome (phy) and
cryptochrome (cry) photoreceptors perceive surrounding light signals and reset the
circadian clock feedback loop, including TOC1 (TIMING OF CAB EXPRES-
SION), CCA1 (CIRCADIAN CLOCK ASSOCIATED 1) and LHY (LATE
ELONGATED HYPOCOTYL) [4-7]. The central feature in the photoperiodic
flowering is the clock generated evening peak of CO (CONSTANS) gene expres-
sion [8]. In long-day (LD) conditions, CO peak coincidences with light resulting
in accumulation of CO protein in the leaf phloem and consequent activation of
the expression of FT (FLOWERING LOCUS T) [9]. FT protein, in turn, moves
to the shoot apex, and together with FD triggers floral initiation by activating
floral identity gene AP1 (APETALA 1) [10,11]. FT, together with SOC1 (SUP-
PRESSOR OF OVEREXPRESSION OF CONSTANS 1) and LFY (LEAFY)
form also convergence points for different flowering pathways, and therefore are
called flowering integrator genes [12].
In winter-annual ecotypes of Arabidopsis, MADS-box gene FLC (Flowering
Locus C) prevents flowering by repressing FT and SOC1, and vernalization is
needed to nullify its function [13]. The major activator of FLC is FRI (FRIGIDA)
[14], but several other proteins, including for example FRL1 (FRIGIDA-LIKE
1) [15], PIE (PHOTOPERIOD INDEPENDENT EARLY FLOWERING 1)
[16], ELF7 and ELF8 (EARLY FLOWERING 7 and 8) [17], and VIP3 (VER-
NALIZATION INDEPENDENCE 3) [18] are also needed to maintain high
FLC expression. During vernalization, FLC is down-regulated by VRN2-PRC2
(Vernalization 2 - Polycomb Repressive Complex 2) protein complex containing
low temperature activated VIN3 (VERNALIZATION INSENSITIVE3), allow-
ing plants to flower [19,20].
Autonomous and GA pathways respond to endogenous cues to regulate flow-
ering time. The role of the autonomous pathway is to promote flowering by low-
ering the basal level of FLC transcription [3]. Autonomous pathway consists of
few sub-pathways, which include for example RNA processing factors encoded
by FCA, FPA, FLK (FLOWERING LOCUS K), FY and LD (LUMINIDEPEN-
DENS) [21], putative histone demethylases LDL1 and LDL2 (LSD1-LIKE 1
and 2) [22], and deacetylases FLD (Flowering locus D) and FVE [23,24]. GA
pathway is needed to induce LFY transcription and flowering in short-day (SD)
conditions [25].
Strawberries (Fragaria sp.) are perennial rosette plants, belonging to the
economically important Rosaceae family. Most genotypes of garden strawberry
