Temporal and spatial regulation of the expression of 1‐aminocyclopropane‐1‐carboxylate oxidase by ethylene in mung bean (Vigna radiata)

Abstract

Ethylene induced an increase in the level of 1‐aminocyclopropane‐1‐carboxylate oxidase (VR‐ACO1) transcript in mung bean hypocotyls. Time course study revealed that the level of the VR‐ACO1 mRNA in excised mung bean hypocotyls increased after 2‐h ethylene treatment and much higher mRNA levels were observed thereafter, while the basal level of transcript was slightly decreased in control tissues. The in vivo ACC oxidase activity increased from 31 nl g−1 h−1 at zero time to maximum activity of 62 nl g−1 h−1 at 10‐h ethylene treatment. Polyclonal antibody against VR‐ACO1 protein expressed in E. coli cells was generated. Immunoblot analysis using the resulting antiserum showed that the induction pattern of ACC oxidase polypeptide was in parallel with that of enzyme activity during the incubation with ethylene. Thus, ethylene increases the levels of the VR‐ACO1 mRNA and ACC oxidase protein as well as enzyme activity in mung bean hypocotyls. The abundance of the VR‐ACO1 transcript and protein was also induced in all parts of light‐grown mung bean seedlings by ethylene treatment. However, both the basal levels and the magnitudes of ethylene‐induction of VR‐ACO1 were markedly different in different tissues, with the roots being the most sensitive to ethylene. These results suggest that the different part of mung bean seedlings has a distinct potential to respond to ethylene with regard to ACC oxidase gene activation. Furthermore, our data suggest that the induction of VR‐ACO1 by ethylene is subject not only to transcriptional control but also to posttranscriptional control in hypocotyls, whereas ethylene regulates the VR‐ACO1 gene expression mainly at the transcriptional level in roots. The possible molecular mechanism of regulation of ACC oxidase gene expression by ethylene and its significance are discussed.

Structure and ethylene-induced expression of the 1-aminocyclopro-pane-1-carboxylate oxidase gene in mung bean (Vigna radiate L.)

“…The results described in Figure 4, as well as those from previous studies (Kim and Yang, 1994;Jin et al, 1999) clearly demonstrate that the level of VR-AC01 transcript markedly increases in response to ethylene in mung bean hypocotyl tissue. However, we still could not determine whether ethylene induced gene expression at either the transcriptional or the posttranscriptional level.…”

“…These results indicate that ethylene is closely associated with the induction of the ACC oxidase gene in fruit tissues. We previously showed that ethylene markedly stimulated the accumulation of ACC oxidase mRNA in mung bean hypocotyls, and suggested that ethylene plays an important role in regulating ACC oxidase gene expression in vegetative mung bean hypocotyl tissue, as it does in fruit tissues (Kim and Yang, 1994;Kim et al, 1997a;Jin et al, 1999). From these results, we might infer that the low, basal level of ACC oxidase transcript constitutively expressed in mung bean hypocotyls is regulated by the endogenous ethylene present in those tissues.…”

“…That expression study demonstrated that VR-AC01 was a major gene that was constitutively expressed in all parts of the seedlings, whereas the relative abundance of the VR-AC02 gene was much lower. Applying 50 BL.L -~ ethylene has been shown to markedly increase the accumulation of VR-AC01 transcript, while ethylene-induction of VR-AC02 is much lower (<5%) in mung bean hypocotyls (Kim and Yang, 1994;Jin et al, 1999).…”

Molecular and Biochemical Characterization of VR-EILs Encoding Mung Bean ETHYLENE INSENSITIVE3-LIKE Proteins

“…Previously, we showed that ethylene markedly stimulated the accumulation of ACC oxidase mRNA in vegetative tissues of mung bean (Kim and Yang, 1994;Jung et al, 2000) and tobacco plants. Based on these results, it has been proposed that ethylene plays a key role in regulating ACC oxidase gene expression in vegetative tissues, as it does in fruit tissue, and that the low basal level of ACC oxidase transcript constitutively expressed in vegetative tissues is regulated by the endogenous ethylene present in these tissues (Kim et al, 1997;Jin et al, 1999). This autocatalysis reaction by ethylene results from the transcriptional activation of the ACC oxidase gene (Park et al, 2001).…”

“…Total RNAs of mung bean and tobacco plants were obtained by a method adapted from the established protocols reviewed by Lizzradi (1983) with modifications as described previously by Jin et al (1999). The total RNAs were precipitated overnight at 4°C by the addition of 0.3 vol of 10 m LiCl and then precipitated in ethanol.…”