Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

134 POSTHARVEST BIOLOGY & TECHNOLOGY OF FRUITS, VEGETABLES, & FLOWERS
receptor results in activation of ethylene responses and onset of normal ripening. Thus,
the inability of the mutant Nr receptor to bind ethylene prevents its inactivation, and in
Nr mutant fruit, ethylene responses are therefore suppressed (Hackett et al., 2000; Tieman
et al., 2000). When NR expression is reduced by antisense technique, expression of LeETR4
increased proportionately. In some manner, the plant compensates for reduced expression of
NR by increasing expression of LeETR4. Thus, the overall receptor content of NR antisense
lines is not substantially affected, whereas the receptor content in LeETR4 antisense lines
is substantially reduced.
Several groups have used the mutant ethylene receptor gene of Arabidopsis etr1-1 to
successfully control the ethylene perception. The initial evidence of the conserved role for
the control of ethylene sensitivity was demonstrated using genetic transformation of the
Arabidopsis etr1-1 mutant gene into the heterologous species tomato and petunia (Petunia
× hybrida). Using the constitutive CaMV 35S promoter to drive the expression of the dominant
mutant Arabidopsis etr1-1 gene, Wilkinson et al. (1997) were able to transform both
species and obtain various ethylene-insensitive phenotypes. The wild-type tomato plants
transformed with etr1-1 displayed flower senescence and never ripe (NR) fruit phenotype,
and etr1-1 petunias produced flowers with delayed senescence after ethylene treatment and
pollination. Further experiments utilizing a constitutive expression of the Arabidopsis etr1-
1 in petunias conferred ethylene insensitivity to the plants, but the constitutive expression
of the gene had some additional negative effects (Clark et al., 1999; Gubrium et al., 2000;
Clevenger et al., 2004). Even though the traits in the transformed petunias were dependent
on the genetic background and temperature, their positive traits included delayed senescence
and flower abscission, while the major negative trait was the poor rooting ability of
the cuttings. Transgenic petunias with etr1-1 under the control of floral-specific promoters
of FBP1 (floral-binding protein) and AP3 (involved in floral development) genes had a vase
life of up to five times that of nontransformed flowers (Cobb et al., 2002).
Bovy et al. (1999) found that expression of the Arabidopsis etr1-1 gene in transgenic
carnations under the control of either its own promoter (CMB2; carnation MADS boxcontaining
promoter), the constitutive CaMV 35S, or the flower-specific petunia FBP1 promoter
delayed flower senescence, resulting in a significant increase in vase life. Transgenic
carnation cut flowers had three times the vase life of nontransformed flowers and lasted up
to 16 days that was longer than flowers treated with either inhibitors of ethylene biosynthesis.
Transgenic chrysanthemum “Sei-Marine” was generated by fusing the promoter of
the tobacco elongation factor 1α (EF1α) gene to DG-ERS1 cDNA and also by introducing
one-nucleotide point mutations corresponding to those present in Arabidopsis etr1-1, etr1-
2, etr1-3, and etr1-4 and tomato Nr resulting in mDG-ERS1(etr1-2), mDG-ERS1(etr1-3),
mDG-ERS1(etr1-4), and mDG-ERS1(Nr) transgenes, respectively (Narumi et al., 2005b).
Among the transgenes tested, the mDG-ERS1 (etr1-4) transgene showed a high ability to
confer reduced ethylene sensitivity in chrysanthemum. This indicated the usefulness of the
mDG-ERS1 transgenes in conferring reduced ethylene sensitivity in chrysanthemum and
gave further support for the action of the DG-ERS1 gene in the perception of ethylene in
chrysanthemum leaves.
Leaf and flower senescence were also delayed significantly in the transgenic coriander
plants transformed with a mutated Arabidopsis ERS protein. The ability of the mutated
ERS1 gene to confer the ethylene-insensitive phenotype can be exploited in extending the
shelf life of leafy vegetables (Wang and Kumar, 2004). Shaw et al. (2002) generated an