Making the Surface of Fleshy Fruit: Biosynthesis, Assembly and Role of the Cuticular Layer - Fruit Ripening: Physiology, Signalling and Genomics - page 89

Table 6.1. Genes involved in cuticle biosynthesis that have been functionally characterized in fl eshy fruit
species.
Gene Species Function Reference(s)

GDSL1 ( CD1 ) Solanum lycopersicum Extracellular

polymerization of cutin
monomers

Isaacson et al. (2009);
Girard et al. (2012); Yeats
et al. (2012)

CYP86A89 Solanum lycopersicum Cutin monomer

biosynthesis

Shi et al. (2013)

CER6 ( KCS6 ) Solanum lycopersicum Very-long-chain fatty acid

elongation

Vogg et al. (2004); Mintz-
Oron et al. (2008)

PS Solanum lycopersicum Decarbonylation of waxes Leide et al. (2011)

TTS2 Solanum lycopersicum Amyrin synthase Wang et al. (2011)

OSC1 and OSC3 Malus domestica Amyrin synthase Brendolise et al. (2011)

F3H Solanum lycopersicum Flavonoid biosynthesis Verhoeyen et al. (2002)

FLS Solanum lycopersicum Flavonoid biosynthesis Verhoeyen et al. (2002)

CHS Solanum lycopersicum Flavonoid biosynthesis Schijlen et al. (2007); Adato

et al. (2009); Ballester et
al. (2010)

ANL2 ( CD2 ) Solanum lycopersicum Homeodomain

transcription factor

Isaacson et al. (2009)

SHINE3 Solanum lycopersicum Apatella transcription

factor

Shi et al. (2013)

MYB12 Solanum lycopersicum MYB domain transcription

factor

Adato et al. (2009); Ballester
et al. (2010)

MYB5b Vitis vinifera MYB domain transcription

factor

Mahjoub et al. (2009)

change in cuticular wax composition.
Chemical analyses of slcyp86a69 mutants
showed a signifi cant reduction in all cutin
monomers in tomato fruit cuticle (Isaacson
et al. , 2009; Shi et al. , 2013). The plants
had an increased susceptibility to
microbial infection as well as an increase
in susceptibility to dehydration stress (see
Plate 4). Enzymatic assays performed with
SlCYP86A89 found that the enzyme
preferentially catalysed the hydroxylation
of C18:1 fatty acid to C18-hydroxyoleic
acid, but it was also able to hydroxylate
C14 and C16 fatty acids (at a signifi cantly
lower activity) (Shi et al. , 2013). This acyl
hydroxylation is a key step in the
biosynthesis of the cutin monomers, as the
hydroxyl groups allow increased branch-
ing during the subsequent polymerization
reactions.

6.4.2 Wax-associated genes in the fl eshy fruit

Genes involved in wax biosynthesis in
fl eshy fruit cuticles have been studied in a
number of species, although tomato is the
species most investigated to date. Mutations
in, or RNA interference knockdowns
of, genes involved in wax biosynthesis
typically lead to a greater increase in water
permeability than observed in cutin
mutants. The composition of the cuticular
waxes of tomato is made up primarily of
n -alkanes followed by triterpenoids and
sterol derivatives and alkanoic acids
(Schreiber, 2010).
An orthologue of the Arabidopsis CER6
has been studied in tomato fruit, where the
gene was shown to encode a E -ketoacyl-
CoA synthase involved in very-long-chain
fatty acid elongation (Vogg et al. , 2004;