Molecular Plant Breeding, 2016, Vol.7, No.16, 1-7
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Figure 2 Ethylene synthesis and signaling are influenced by multiple factors including Abiotic and biotic factors, developmental cues
and plant hormones that alter plant processes from germination to senescence. (Idea taken from Yoo SD, Cho Y, Sheen J. 2009.
Emerging connections in the ethylene signaling network. Trends Plant Sci. 14(5):270-9. doi: 10.1016/j.tplants.2009.02.007. Epub
2009 Apr 15.)
A linear ethylene signal pathway has been recognized
based on genetic and molecular analyses of ethylene
response mutants starting from hormone perception at
the membrane to transcriptional regulation in the
nucleus (Bleecker and Kende, 2000 ; Chang and
Stadler, 2001). Ethylene is sensed by transmembrane
receptors. CTR1 as a negative regulator of this
pathway is present downstream to receptors.
Downstream of CRT1, ethylene receptors EIN2 and
EIN3, EIN5, and EIN6 are present as positive
regulators while EIN3 intercede transcriptional
cascade of ethylene-regulated genes (Chen et al., 2005;
Guo and Ecker, 2004). There are various families of
ethylene induced genes that are present downstream of
EIN3 like transcription factors (EIL) or proteins
including ethylene response factor (ERF) and ethylene
response DNA-binding factor (EDF) that signifying
and demonstrating the transcription cascade that
works downstream of EIL proteins (Figure 3). On the
basis sequence and structural similarities, ethylene
receptors present in different plant species are
categorized into two groups. Group I receptors
consists of ETR1 and ERSI whereas ETR2, EIN4, and
ERS2 are the members of group II receptors in
arabidopsis. Ethylene on binding to receptors leads to
the inactivation of these receptors (Hua and
Meyerowitz, 1998). Thus absence of ethylene
supposed to be the basis of the activation of CTRI that
is the negative regulator of ethylene signaling pathway
(Kieber et al., 1993).
Binding of ethylene to its
receptors is allied with its co-factor that is copper,
which is carried by the copper transporter RAN
(Tuteja, 2007).
Although clear functional attributes of EIN2, EIN5,
and EIN6 at molecular level has not been cleared yet.
However EIN2 is an integral membrane protein while
EIN3 is a nuclear protein and as a transcription factor
