Biotechnology of Fruit Quality - Fruit Ripening: Physiology, Signalling and Genomics - page 269

shapechromosome fs8.1 ) regulate fruit
shape with minimum effect on fruit size;
and fasciated ( fas ) and locule number ( lc )
determine carpel number and affect both
fruit size and shape (Ku et al. , 2000;
Rodríguez et al. , 2011a). fw2.2 , cloned by
high-resolution positional mapping, has
been reported to share homology with the
cell-membrane-localized Ras-like G-protein
(Frary et al. , 2000) and negatively regulates
fruit size. A mutation in its 2.7 kb
upstream promoter region resulted in null
expression and a large tomato fruit
phenotype (Nesbitt and Tanksley, 2002).
fw2.2 has been further shown to suppress
the anticlinal, but not periclinal, cell
division in the placenta and pericarp,
causing a reduction in the fruit length-to-
perimeter ratio but not the pericarp
thickness (Liu et al. , 2003). In pepper
( Capsicum chinense and Capsicum
frutescens ), fw2.1 , but not fw2.2 , is the
single major fruit-weight QTL responsible
for 62% of the trait variation (Zygier et al. ,
2005; Ben Chaim et al. , 2006).
Fruit size and weight are a function of
the number of cells within the ovary prior
to fertilization and cell expansion (Bohner
and Bangerth, 1988). Additionally, endore-
duplication, which increases cell ex-
pansion, contributes to the fi nal fruit size
(Cheniclet et al. , 2005). Cyclins and cyclin-
dependent kinase (CDK) complexes
regulate the progression of cell division,
while CDK inhibitors such as WEE1 induce
endoreduplication (Sun et al. , 1999).
Expression of antisense Slwee1 under the
control of the caulifl ower mosaic virus
(CaMV) 35S promoter reduced ploidy
levels, fruit mass, plant growth and seed
size (Gonzalez et al. , 2007). Another gene
that promotes endoreduplication is cell
cycle switch CCS52A ), arresting cell
division (Cebolla et al. , 1999). Over-
expression of CCS52A , which activates
anaphase-promoting complex E3 ubiquitin
ligase, led to increased tomato fruit size
(Mathieu-Rivet et al. , 2010).
A retrotransposon-mediated gene
duplication at the sun locus resulted in
morphological variation of tomato fruit

(Xiao et al. , 2008). Overexpression of
IQD12 , one of the fi ve genes at the sun
locus, signifi cantly increased fruit elong-
ation, while impairing its expression by
RNAi signifi cantly decreased fruit elong-
ation (Xiao et al. , 2008). The molecular
function of IQD12 is not yet known, but it
exhibits homology with a member of the
IQ67 protein family containing the
calmodulin-binding domain and probably
changes the fruit shape by affecting the
pattern along the apical-basal axis (Xiao
et al. , 2008). The ovate locus, another
important QTL responsible for the
development of a pear-shaped instead of an
oval-shaped tomato fruit, encodes a tran-
scription repressor regulating GA20ox1 , a
gibberellic acid (GA) biosynthesis enzyme
(Wang et al. , 2007). Overexpression of the
ovate family protein 1 gene, OFP1 , reduced
fruit elongation in tomato (Ku et al. , 1999)
and pepper (Tsaballa et al. , 2011).
Complementation of pear-shaped fruit
phenotype TA503 by either native OVATE
or ectopic overexpression of OVATE under
the control of the CaMV 35S promoter
( 35S:OVATE ) produced round-shaped fruit
(Liu et al. , 2002). Silencing of OVATE in
round-fruited pepper cv. 'Mytilini' resulted
in increased expression of GA20ox1 and an
oblong-shaped fruit (Tsaballa et al. , 2011).
The molecular identity of genes present at
other QTLs determining fruit shape and
size including fs8.1 , fs10.1 , fs3.1 , fas , and
lc remains to be determined. Similarly,
biochemical signals regulating fruit size
and shape genes are also still largely
unknown (Handa et al. , 2012). It will be
interesting to explore downstream and
upstream regulators of these QTLs through
which these loci impart their effect on fruit
quality attributes such as size and shape.
Although the fruit shape and size genes
can be used to alter fruit architecture by
molecular genetics approaches, they have
not yet been used to develop fruit with a
novel architecture for commercial pur-
poses. However, all emerging evidence
indicates that these genes would provide a
rich resource to develop desirable fruit
phenotypes.