Biotechnology of Fruit Quality - Fruit Ripening: Physiology, Signalling and Genomics - page 268

lycopersicum ) mutants has added to our
knowledge on the regulatory mechanisms
underlying the fruit ripening process
(Giovannoni, 2004). Molecular genetics has
provided many additional tool kits that
have enhanced the molecular engineering
of crop plants. These include plant trans-
formation methods that have made the
candidate gene approach a reality to test
the phenotypic role of a particular gene by
altering its expression during plant growth
and development (Fatima et al. , 2009). The
gain-of-function (ectopic overexpression)
or loss-of-function (repression by antisense
RNA interference (RNAi)) approaches have
made it possible to characterize the
phenotypes associated with a single gene
and its potential to regulate desirable
phenotype in crop plants. This chapter
summarizes some of the progress made
using these tools to enhance fruit quality
attributes.
Fruits are derived from different parts of
a fl ower, including the infl orescence, and
have enormous diversity in their structure
and physiological functions (Handa et al. ,
2012). As development, maturation and
ripening of diverse classes of fruits differ
signifi cantly, it is a challenge to improve
quality attributes of a chosen fruit by
biotechnology. None the less, many bio-
chemical and regulatory mechanisms
impacting the quality of fruits during
ripening are similar, and therefore it is
possible to genetically alter ripening and/
or slow down deterioration to enhance
fruit quality. Ethylene is a gaseous plant
hormone decidedly integral to fruit
ripening, especially in fruit types that have
a burst of respiration during ripening,
classifi ed as climacteric fruits (Mattoo and
Suttle, 1991; Abeles et al. , 1992). The
elucidation of its biosynthesis and per-
ception has eased biotechnological strat-
egies to regulate ripening and senescence
processes in plants. Thus, regulation of
both production and perception of
ethylene in fruit crops via molecular
engineering has led to remarkable effects
on various aspects of fruit quality (Lin et
al. , 2009; Klee and Giovannoni, 2011), a
topic discussed in Part III of this topic.

Molecular engineering of a number of fruit
crops including apple, banana, berries,
citrus, cucumber, grape, melon, potato,
aubergine and tomato is the subject of
research in many laboratories worldwide.
Tomato has become a model fruit crop of
choice to elucidate the role of various
genes in fruit quality (Giovannoni, 2007;
Fatima et al. , 2009; Klee and Giovannoni,
2011). In this chapter, we have focused
primarily on the molecular engineering of
shape, size, texture, phytonutrient levels
and volatiles in tomato fruit and also make
reference to genetic engineering studies in
other fruit crops.

16.2 Molecular Engineering of Fruit
Appearance

Fruit size and shape are attributes that are
quantitatively inherited and determine
yield and consumer appeal in most fruit
crops. These attributes were given consider-
able attention during the domestication and
selection of new fruit cultivars (Rodríguez
et al. , 2011a). During domestication, small
fruited wild-type Solanum pimpinelli-
folium was developed to larger fruit
varieties such as Giant Heirloom. In the
process, the fruit mass of 1-2 g per fruit
was increased to over 1000 g per fruit and
locule numbers from two to more than ten
(Lippman and Tanksley, 2001). Other fruit
species were also bred for similar increases
in size during domestication of their wild
progenitors (Smartt and Simmonds, 1995).
The application of molecular marker and
high-resolution fi ne-mapping approaches
made it possible to identify QTLs and
genes encoded within these loci affecting
fruit size and shape. In tomato alone, over
30 QTLs have been identifi ed, although
only ten of them contribute to most of
the observed phenotypic variation
(Grandillo et al. , 1999; Doganlar et al. ,
2002; van der Knaap et al. , 2002; Tanksley,
2004; van der Knaap et al. , 2004). Among
them, fruit weight ( fw2.2 ) controls fruit size
without affecting fruit shape or seed
production (Frary et al. , 2000; Cong et al. ,
2002; Liu et al. , 2003); sun , ovate and fruit