No.42 - è¾²æ¥çç©è³æºç 究æ
No.42 - è¾²æ¥çç©è³æºç 究æ
No.42 - è¾²æ¥çç©è³æºç 究æ
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42<br />
Takashi HIRAYAMA and Tsutomu UGAJIN<br />
specific ethylene response mutant hls1 and eir1; enhanced ethylene sensitive mutant, eer1; finally,<br />
altered ethylene recognition mutant, ran1. Based on the results from extensive genetic studies with<br />
these mutants, a model has been drawn for the ethylene-signaling pathway, in which identified<br />
components act in a linear pathway (Figure 1) (GUZMAN and ECKER 1990). Isolation of the<br />
corresponding genes and molecular analysis of encoded proteins have greatly facilitated our<br />
understanding of the ethylene-signaling pathway at the molecular level.<br />
Ethylene receptors<br />
Based on the genomic sequence, Arabidopsis has five ethylene receptors, namely, ETR1,<br />
ERS1, ETR2, EIN4 and ERS2. Structure of ethylene receptor protein is reminiscent of membranespanning<br />
histidine kinase. The three N-terminal membrane-spanning domains are necessary and<br />
sufficient for ethylene binding. This region is highly conserved among ethylene receptors. Analysis<br />
of mutants such as etr1-1 and knock-out mutants have shown that ethylene receptors negatively<br />
regulate down stream components (HUA and MEYEROWITZ 1998). In the absent of ethylene<br />
molecule, ethylene receptors are active and inhibit the ethylene response. On the other hands, in<br />
the presence of ethylene, ethylene receptors become inactive and let downstream ethylene-<br />
Figure 1 The ethylene-signaling pathway drawn based on the results obtained from genetic<br />
analyses. Genetically identified components involved in the ethylene response are<br />
shown. The allow heads indicate only the direction of the signal. RAN1 and EER1<br />
function as modifier for ethylene receptors and CTR1, respectively (see text).
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