Ethylene Perception and Gene Expression - Postharvest Biology and Technology of Fruits, Vegetables, and Flowers - page 133

acid biosynthesis), which blocked ethylene production in the flowers. These results indicate
that the DC-ERS2 and DC-ETR1 genes are not subject to positive regulation by ethylene, and
the decrease in the levels of their mRNAs in senescing petals is caused by some unidentified
senescence factor(s) other than ethylene (Shibuya et al., 2002).
In the cut flowers of “Seiko-no-makoto” (ethylene-sensitive cultivar) chrysanthemum
( Dendranthemagrandifloru (Ramat.) Kitamura), DG-ERS1 mRNA was present in a large
amount in the petals on day 0 (at the full-opening stage of flower) and its levels decreased
markedly with the lapse of time in air or in response to a 12-h exposure to ethylene,
although these were not evident in “Iwa-no-hakusen” chrysanthemum (ethylene-insensitive
cultivar). DG-ERS1 mRNA was present in a large amount in nonsenescent flower tissues of
an ethylene-sensitive “Seiko-no-makoto” cultivar, but its mRNA level was very low in an
ethylene-insensitive “Iwa-no-hakusen” cultivar. The observed difference between the two
cultivars is probably related to the variation in sensitivity to ethylene between them, and
suggest that the DG-ERS1 gene and its resultant DG-ERS1 protein may be involved in the
perception of ethylene signal in flower and leaf tissues of the cut chrysanthemum, especially
those of “Seiko-no-makoto” (Narumi et al., 2005a).
Two ethylene receptor paralogous genes, GgERS1a and GgERS1b , have been iso-
lated from gladiolus ( Gladiolusrandiflo a hort cv. Traveler), an ethylene-insensitive flower
(Arora et al., 2006). The cDNA sequence indicated that both genes have almost exact sim-
ilar sequence except that GgERS1b lacks 636 nucleotides, including first (H) and second
(N) in the histidine kinase motifs, present in GgERS1a . The analysis of the genomic DNA
sequences (4,776-bp nucleotide designated as GgERS1 long DNA and 3,956-bp nucleotide
designated as GgERS1 short DNA) revealed that both sequences were identical except that
GgERS1 short DNA was devoid of an 820-bp long nucleotide segment in the first intron of
GgERS1 long DNA. These data suggested that each of the GgERS1 genes was generated
by duplication and splicing from different genomic DNA. The GgERS1b mRNA level de-
creased in petals during flower development, whereas the expression of GgERS1a mRNA
was constitutive, however, with a high accumulation level, suggesting that high expression
level of GgERS1a conferred the ethylene insensitive nature in petals of gladiolus. On the
other hand, the sensitivity to ethylene might be regulated by GgERS1b expression.
6.5 Control of ethylene perception
Ethylene receptors have been postulated to function via the “receptor inhibition” model
in Arabidopsis in which absence of ethylene results in active receptors and repression
of ethylene responses (Hua and Meyerowitz, 1998). In the presence of ethylene, receptors
switch to an inactive state, and responses such as the triple responses are observed. Attempts
to control ethylene perception by decreasing ethylene sensitivity and improve postharvest
quality have been carried out on various horticultural plant products using such approaches
as antisense RNA or transformation with a gene coding for a mutant receptor that does not
bind ethylene and which constitutively suppresses the normal ethylene responses.
An important aspect of the control of ethylene perception was identified by analysis
of transgenic tomato plants with reduced expression of individual receptors. Antisense
reduction in LeETR4 expression resulted in earlier and accelerated fruit ripening and higher
levels of lycopene accumulation (Tieman et al., 2000). Some of the antisense lines also
synthesized significantly more ethylene than wild-type fruits. Antisense inhibition of Nr