Ripening Mutants - Fruit Ripening: Physiology, Signalling and Genomics - page 258

elastic properties, although these changes
did not result in altered cuticular per-
meability (Adato et al. , 2009). Mutant
alleles at the y locus do not express
SlMYB12 and, although SlMYB12 com-
plements the y mutation, the exact
molecular basis for the mutation remains
unknown (Adato et al. , 2009; Ballester et
al. , 2010).
Mutant loci that infl uence anthocyanin
accumulation in diverse fruit crop species
have been identifi ed, and several of these
loci have been attributed to altered activity
of MYB transcription factors that directly
regulate anthocyanin biosynthesis. In
pepper, the dominant A locus controls
anthocyanin accumulation in pepper fruit
through increased expression of a MYB
transcription factor homologous to
ANTHOCYANIN 2 of petunia (Borovsky et
al. , 2004). Recently, the Anthocyanin fruit
( Aft ) locus of tomato, which is derived
from introgression of a chromosomal
segment from the wild tomato species
Solanum chilense into cultivated tomato,
was attributed to increased activity of the
wild species allele of a second MYB tran-
scription factor known as ANTHOCYANIN
1 (Schreiber et al. , 2012). Similarly, red-
fl eshed apple varieties can be attributed to
ectopic expression of MdMYB10 , and
differential methylation within the
promoter region of MdMYB10 correlates
with its altered expression and the
presence of red stripes versus green stripes
in some apple varieties (Chagne et al. ,
2007; Espley et al. , 2007; Telias et al. ,
2011). The presence of transposable
element insertions in MYB transcription
factors also alters anthocyanin pig-
mentation in fl eshy fruit. A retrotransposon
insertion into VvmybA1 in grape ( Vitis
vinifera ) disrupts function leading to loss
of anthocyanin pigmentation in white-
fruited varieties (Kobayashi et al. , 2004).
Conversely, distinct retrotransposon in-
sertions within the promoter regions of a
MYB gene from blood orange confer its
cold-dependent fruit-specifi c expression,
leading to an increase in anthocyanin
formation (Butelli et al. , 2012). Together,
these

mechanisms have evolved to control MYB
gene expression and anthocyanin bio-
synthesis in diverse fruit crop species.

15.6 Cuticle and Wax Biosynthesis
Mutants Alter the Physical Properties of
Fruit Surfaces

The aerial surfaces of terrestrial plants are
covered with a cuticle, a heterogeneous
lipid-based polymer comprised of cutin,
together with intra- and epicuticular waxes
and polysaccharides (Pollard et al. , 2008).
The cuticle forms a structural framework,
acts as the principal barrier to restrict non-
stomatal water loss, possesses refl ective
properties that reduce heat load and limit
the effects of UV radiation, and forms an
anti-adhesive layer that helps protect
against insect feeding and pathogen
infection (Bargel et al. , 2006). Many of the
genes involved in the synthesis and
transport of cutin and waxes have been
identifi ed and characterized in Arabidopsis
(Li-Beisson et al. , 2010). However, the
cuticle is of central importance to the
quality of fl eshy fruits, and mechanical
failure of the cuticle can result in either
pre- or postharvest cracking leading to crop
losses (Dominguez et al. , 2011). Further-
more, signifi cant cuticle lipid deposition
can occur in some fl eshy fruits, particularly
tomato, where the cuticle can be up to 10
μm thick, yielding more than 1 mg cm -2
(Isaacson et al. , 2009; Nadakuduti et al. ,
2012). The cuticular lipid deposition,
coupled with the importance of tomato as a
model crop species has driven interest in
examining the physical and chemical
properties of tomato fruit cuticles, and
several studies have utilized either
genomics- or proteomics-based approaches
to identify genes and proteins preferentially
associated with epidermal cells and cuticle
deposition (Mintz-Oron et al. , 2008;
Samuels et al. , 2008; Yeats et al. , 2010;
Dominguez et al. , 2011; Matas et al. , 2011).
Tomato mutants have been char-
acterized that alter the properties of the
fruit cuticle. Fruits of the cutin defi cient 1 ,
2 and 3 ( cd1 , cd2 and cd3 ) mutants exhibit data illustrate that different