Table 1. Transgenic crops with altered phenotype, senescence and ripening due to overexpression and suppression of ethylene receptor and downstream signaling molecules.

Crop	Gene	Function of the Gene	Expression	Effect/Phenotype	Conclusion	References
Tomato	NR (Receptor gene) Semi Dominant	Functionally redundant ethylene insensitive in all tissues.	Antisense suppression	Normal ripening as in wild type fruit. No effect on ethylene sensitivity, increased levels of LeETR4 mRNA. No effect on ethylene sensitivity of seedlings	Not essential for ripening. Ethylene perception and signaling via the NR receptor is consistent with the receptor inhibition model. Functional compensation of LeETR4 for reduced NR expression	Hackett et al., 2000172 Lanahan et al., 1994163 Tieman et al., 2000167
		NR (Never Ripe) Semi Dominant	Functionally redundant ethylene insensitive in all tissues.	Overexpression in LeETR4 suppressed lines	Eliminates ethylene sensitivity, lack of epinasty, flower senescence and normal fruit set, rescued the ethylene response phenotype.	Proves the functional redundancy of the receptors. Negative Regulators of ethylene response. Only associated with ripening.	Tieman et al., 2000167
		Nr (Mutant NR gene)	Unable to bind ethylene, delay senescence, imparts ethylene insensitivity.	Antisense suppression	Activated ethylene responses and onset of normal ripening, plant with two homozygous copies of transgene produced wild type fruit. Single gene in a homozygous state gave intermediate phenotype.	Threshold level of mutant receptor is needed to suppress the ethylene response pathway. Support receptor inhibition model.	Hackett et al., 2000172 Lanahan et al., 1994163
		LeEIL(1-3) Transcription Factor	Functionally redundant, positive regulator of ethylene signaling.	Antisense suppression	Single LeEIL suppression results no change. Multiple LeEIL gene suppression delays leaf epinasty, flower abscission, flower senescence.	Normal levels of expression of the other two LeEILs can compensate for the loss of single gene.	Tieman et al., 200123
		LeEIL1 in tomato Nr mutant	Functionally redundant, positive regulators of multiple ethylene receptors.	Overexpresession in ethylene insensitive non ripening Nr mutant of tomato	Partial restoration of ripening. Seedling triple response, upregulation of all ripening related genes were not restored.	LeEIL1 may not have expressed at sufficiently high levels to restore these functions,LeEIL2, LeEIL3 are also required.	Chen et al., 2004175
		LeEIN2	Positive mediator of ethylene signaling and fruit development	Suppression (VGIS)	Delayed fruit development and ripening with fewer seeds and locules, suppressed ethylene inducible and ripening related genes, partially blocked ripening with large green parthenocarpic sector on fruit	Probable involvement of LeEIN2 in a crosstalk between ethylene and auxin during fruit development	Zhu et al., 2006174
		LeETR4	Imparts ethylene in sensitivity, delay the onset of ripening until the seeds have matured.	Suppression	Increased ethylene sensitivity, fruits ripen prematurely flower senesce early without an increase in ethylene level. Severe epinastic curvature of petioles, no change in the levels of NR.	Negative regulator of the ethylene signaling pathway, lowering the receptor levels increases sensitivity to ethylene. An important regulator of ripening	Tieman et al., 2000167
		LeETR4 using immature fruit specific Tfm7 promoter	Delays onset of ripening in immature fruits	RNAi mediated suppression	Early ripening, total yield, fruit size and flavour related chemical composition had no negative effect. Leaves and other tissues were unaffected.	Tissue specific approach to hasten fruit development without unwanted effects and enhanced ethylene response by ethylene receptor depletion.	Kevany et al., 2008171
		LeETR1	Functionally redundant	Antisense expression of receiver domain and the 3′ UTR of LeETR1	Delayed abscission and shorter internodes with no effect on ethylene sensitivity, normal triple response, and reduced auxin movement. No effect on NR transcripts.	Receiver domain of LeETR1 and LeETR2 has a role to play in signaling and can not be compensated by NR receptor	Whitelaw et al., 2002176
		etr1-1 (mutated ethylene receptors from Arabidopsis)	Imparts dominant ethylene insensitivity	Overexpression	Long thin hypocotyls, normal root growth, more open and expended apical regions. Fruits with delayed ripening and senescence similar to Nr mutants	Confers ethylene insensitivity in heterologous plants	Wilkinson et al., 1997112
	LeETR1 and LeETR2	Non redundant, plays role in ethylene perception	Antisense suppression	Shortened, thickened hypocotyls, enhanced abscission of petiole explants, faster senescence of flowers both in presence and absence of flowers.	LeETR1 might have a more specific role to play in signaling, each member has a specific role to play and are not totaly redundant.	Wang et al., 2003170
Carnation	etr1-1 using CaMV 35S promoter	Imparts global ethylene insensitivity	overexpression	Diminished ethylene insensitivity and diseased resistance with delayed senescence. No petal inrolling, firm petals.	Heterologous expression imparts insensitivity in carnation	Bovy et al., 199979
	etr1-1 using flower specific fbp1 promoter	Imparts global ethylene insensitivity	overexpression	Delayed flower senescence with increased disease resistance. Ethylene sensitivity increased in other parts of flower apart from petals, better seed germination and reduced leaf abscission.	Flower specific promoter fixes the compromised disease resistance status	Bovy et al., 199979
Petunia	etr1-1/Nr	Imparts global ethylene insensitivity	overexpression	Ethylene insensitivity with delayed flower senescence. Turgid corollas of flower, delayed abscission.	Cross species transfer	Wilkinson et al., 1997112
	etr1-1 using flower binding protein from Petunia (fbp1) or apetala 3 promoter from Arabidopsis	Imparts global ethylene insensitivity	overexpression	Diminished disease resistance and reduced adventitious root hair formation, increased ethylene insensitivity with delayed senescence, seedling root hair formation observed. 73% of fbp1 and 32% of ap3 plants showed more than 100% increase in flower life.	Flower specific promoter enhances disease resistance in cross species transfer	Cobb et al., 2002114
	boers (mutated form of BOERS from Brassica oleracea)	Imparts ethylene insensitivity	overexpression	Plants retained turgidity and pigmentation longer, larger flowers, extended flower longevity, diminished disease resistance with higher mortality, increased ethylene evolution and reduced ethylene sensitivity, self incompatible.	boers is a dominant allele imparting insensitivity in the heterozygous transformed plants	Shaw et al., 2002177
	PhEIN2 (downstream signaling protein)	Involved in regulation of accumulation of EIN3 and EIL1 proteins. Positive regulators of ethylene cascade	Suppression by expressing sense RNA and RNAi mediated silencing	Transgenic lines using sense RNA expression showed moderate delay in flower senescence and fruit ripening with no premature death reported. RNAi construct suppressed lines showed great delay in flower senescence and fruit ripening with great deal of premature death. Corollas were turgid even after the ovaries were turgid.	Reduced or inhibited adventitious root formation (sense RNA expression) Reduced ethylene sensitivity (RNAi suppression)	Shibuya et al. 2004119
Coriander	AtERS1 (mutated dominant receptor)	Confers ethylene insensitivity	overexpression	Delayed leaf senescence with prolonged total chlorophyll content in transgenic leaves, delayed flower senescence.	Delayed senescence is not due to drastic reduction in ethylene biosynthesis rather it is due to the effect of dominant negative ERS1 transgene. Distantly related crop species can have extended shelf life exploiting heterologus gene transfer.	Wang and Kumar 200491
Campanula	etr1-1 with fbp1	Imparts global ethylene insensitivity	Overexpressed	Enhanced tolerance to exogenous ethylene and reduced ethylene sensitivity, stably passed to next generation of plants, weak expression of etr1-1 in leaves, intact fertility and no compromise on disease resistance.	Sensitivity to ethylene in plants is independent of the copy number of the T-DNA.	Srikandarajah et al., 200757
Nemesia	CmETR1/H69A, missensed mutated ethylene receptor from Cucumis melo	Imparts reduced ethylene sensitivity	Overexpression	Delayed flower senescence by 1--3 days and lesser root hair formation compared to non transgenic wild type.	Artificially mutated ethylene receptor gene conferred reduced ethylene sensitivity in heterologus plants	Cui et al., 2004109
Lettuce	CmERS1/H70A	Imparts stable sterlity, reduced fertility along with ethylene insensitivity	Overexpressed	Apart from reduced ethylene sensitivity, induced sterility in vegetatively propagated plants and pollen propagated plants	This mutated receptor gene checks the pollen dispersal from transgenic plants and prohibit unwanted development of traits in other plants and weeds, can induce sterility in heterologus transgenic plants.	Takada et al., 2007140
Chrysanthemum	mDG-ERS1 (etr1-4), mutated nucleotide substitution corresponding to etr1-1.	Imparts ethylene insensitivity	Overexpressed	Delayed leaf yellowing on exposure to exogenous ethylene and leaves on lower part of stem remain attached to it without yellowing, reduced ethylene sensitivity, detached shoots in darkness without ethylene treatment showed reduced senescence.	Heterologus gene transformation remained unsuccessful; the mutated receptor could work for compositae family members.	Narumi et al., 2005b85 Satoh et al., 2006, 2007, 200887,88,89
	Cm-ETR1/H69A (missensed mutated ethylene receptor from Cucumis melo)	Imparts ethylene insensitivity, male sterility, prevents transgene flow via pollen	Overexpression	Drastic reduction in number of pollen grains at temp 20--35 °C but observed at 10-15 C. Due to suppression of Cm-ETR1/H69A expression at low temperature and optimal growth temp for plant at 15--20 °C. Female fertility was also reduced.	Optimal growth temperature for Chrysanthemum collides with its vegetative, reproductive growth resulting in mature pollens to flourish	Shinoyama et al., 201290
Lotus	Atetr1-1	Mutated dominant ethylene insensitive ethylene receptor	Overexpression	Delayed abscission and senescence of petals, ethylene insensitive, twisted coiled hypocotyls, no triple response, fewer lateral roots, 7-fold increased nodulation in highly ethylene insensitive transformants, 1.7-fold increases in bacteroid infection.	Multiple roles of ethylene in nodule initiation by influencing root cell interactions and radial positioning, independent of autoregulation and nitrate inhibition of nodulation	Lohar et al., 2009105
	Cm-ERS1/H70A	Inhibits ethylene sensitivity, promotes root nodulation.	Overexpression	Confers ethylene insensitivity and fixes the transgene in T3 generation, reduced ethylene sensitivity due to 1-ACC resistance, increased flowering	Transgenic alteration of ethylene perception alters the rhizobial infection and nodulation phenotype.	Nukui et al., 2004104
Cucumber	At-etr1-1 with CaMV 35S, AP3, CRC promoter	Imparts dominant ethylene insensitivity	Overexpression	Prevents carpel development resulting in male flowers with CaMV35S promoter. Increased femaleness and conversion of bisexual to female buds with CRC promoter. Exclusive male flower production with AP3 promoter.	Heterologus ethylene insensitivity. Ethylene perception is required to promote femaleness in melon. Dual role of ethylene in sex expression and carpel maturation. Site for ethylene perception lies in stamen primordia and not in carpel primordial.	Little et al., 2007145