No.42 - è¾²æ¥­ç”Ÿç‰©è³‡æºç ”ç©¶æ‰€

48
Takashi HIRAYAMA and Tsutomu UGAJIN
This idea is consistent with the weak ethylene insensitive phenotype of the ein3 mutants.
Future perspective
As described above, the over all structure of the ethylene-signaling pathway, from the
perception to the gene expression, has been elucidated through the studies using Arabidopsis
(Figure 3). Orthologues for Arabidopsis ethylene-signaling components have been found in other
plant systems, including tomato, maize and rice. Therefore the ethylene-signaling pathway
described here presumably is common in large parts in plant kingdom.
Figure 3 Schematic representation of a model for the ethylene-signaling pathway. Ethylene receptor
binds a copper ion presumably during protein modification in the Golgi apparatus. Copper
ion is delivered by RAN1 copper transporter. Ethylene receptor seems to localize to the ER
membrane although this is still controversial. The subcellular localization of EIN2 is not
elucidated yet. EIN2 might sense some signals although there is no evidence. EIN3 functions
in the nuclear although it is not clear if EIN3 localizes to the nuclear in the absence of
ethylene or not. In the absence of ethylene, ethylene receptor and CTR1 are active and
presumably inhibit EIN2. When ethylene receptor recognizes ethylene molecule, it turns off
and consequently allows EIN2 to activate EIN3 somehow. Activated EIN3 induces the
expressions of the ERF1 gene and some ethylene responsive genes (not illustrated). Produced
ERF1, a transcriptional factor, in turn activates ethylene responsive genes.