Climacteric and Non-climacteric Ripening - Fruit Ripening: Physiology, Signalling and Genomics - page 9

melon in a different study (Ezura et al. ,
2002). Climacteric-type melons have also
been created from two non-climacteric
melons, Piel de Sapo (var. inodorus ) and
PI161375 (var. chinensis ) (Moreno et al. ,
2008). However, the genetic position of the
quantitative trait loci associated with
ethylene production and respiration rates
in this study did not coincide with the Al
loci described by Périn et al. (2002). These
results suggest, at a minimum, that the
climacteric trait is dominant and not
determined by only a single locus.
In conclusion, non-climacteric-type
fruits derived from species that have both
climacteric and non-climacteric varieties in
the same genus may be generated by the
loss or repression of function of fruit
ripening-related gene(s). Conversely, fruits
that are classically categorized as non-
climacteric, such as strawberry, grape and
citrus, have not been found to show these
variations in ethylene production levels,
although they do show variations at low
ethylene levels. A concrete distinction
between climacteric and non-climacteric
types may be formulated based on these
results, whereas novel data suggest the
involvement of ethylene in classical non-
climacteric fruits.

restored by exogenous ethylene, although
ethylene-regulated gene expression can be
partially restored (Griffi ths et al. , 1999;
Thompson et al. , 1999; Barry et al. , 2000);
i.e. these mutants do not lose functional
ethylene perception and signalling. Con-
versely, these observations suggest that the
mutations in rin , nor and Cnr affect the
ripening cascade upstream of ethylene and
are involved in both ethylene-dependent
and -independent ripening pathways.
In the rin mutant tomato, LeMADS-RIN ,
a SEPALLATA ( SEP )-like MADS-box tran-
scription factor, was identifi ed at the rin
locus (Vrebalov et al. , 2002). Genetic
complementation and antisense experi-
ments confi rmed that LeMADS-RIN acts
both upstream of the ethylene cascade and
in an ethylene-independent pathway. Data
from chromatin immunoprecipitation
studies have revealed that RIN interacts
with the promoter of ripening-related genes
- including the transcriptional control
network involved in the overall regulation
of ripening, ethylene biosynthesis, ethyl-
ene perception (downstream of the ethyl-
ene response), cell-wall metabolism and
carotenoid biosynthesis - and directly
controls these processes at the tran-
scriptional level during ripening (Ito et al. ,
2008; Fujisawa et al ., 2011; Martel et al. ,
2011). Intriguingly, the FaMADS9 tran-
scription factor identifi ed in strawberry
had a similar biological function to that of
LeMADS-RIN , as antisense strawberry fruit
led to the inhibition of normal develop-
ment and ripening of the petal, achene and
receptacle tissues (Seymour et al. , 2011).
Taken together, these results indicate that
RIN -like genes play a central role as master
regulators of the ripening cascade in both
climacteric and non-climacteric fruits (Fig.
1.2).

1.5.1 Common programmes of climacteric
and non-climacteric ripening

Classically, fl eshy fruits have been clas-
sifi ed into two categories according to their
dependence on ethylene for fruit ripening:
climacteric and non-climacteric. However,
the ripening phenomena of both classes,
including changes in colour, texture and
fl avour, have much in common. As a
common point, the ripening processes in
climacteric fruits are controlled by an
ethylene-independent pathway similar to
that in non-climacteric fruits in parallel
with an ethylene-dependent pathway (see
Section 1.3.2 for further details). In certain
non-ripening tomato mutants, such as
ripening-inhibitor ( rin ), non-ripening ( nor )
and Colourless non-ripening ( Cnr ) mutants,
the inhibited ripening phenomena are not

1.6 Conclusions

The advancement of experimental tech-
niques and tools has elucidated many fruit-
ripening mechanisms at the physiological,
genetic and molecular levels. The data
summarized here provide novel insights