Ethylene regulation of an ERS1 homolog in mung bean seedlings

Abstract

ETR1 (ethylene resistant) and ERS1 (ethylene response sensor) have been shown to act as a receptor for ethylene in Arabidopsis. We isolated a full length cDNA clone (VR‐ERS1) encoding the ERS1 homolog from mung bean hypocotyls by screening a cDNA library with a partial cDNA fragment obtained by the reverse transcriptase‐polymerase chain reaction (RT‐PCR) method. VR‐ERS1 is 2 477 bp long and contains a single open reading frame encoding 636 amino acids (Mr=70.9 kDa). The predicted amino acid sequence shares a high degree of identity (72–78%) with other ERS1 homologs from Arabidopsis, tomato and Rumex palustris, and is 39% identical to Arabidopsis ERS2. Genomic Southern blot analysis using a gene‐specific probe suggests the existence of one copy of the VR‐ERS1 gene in the mung bean genome. Northern hybridization indicates that the level of VR‐ERS1 transcript varies in different parts of dark‐ and light‐grown mung bean seedlings, with the greatest amount of the transcript being detected in apical hooks. Results showed that the abundance of the message was highly inducible by ethylene in all tissues examined. However, the magnitudes of ethylene‐induction of VR‐ERS1 were significantly different in each part of mung bean seedlings, with the leaf tissue being most sensitive to ethylene and there being an 8‐fold increase in mRNA level after 6 h ethylene treatment. These results suggest that ethylene positively modulates the expression of its receptor gene in the vegetative tissues of mung bean plants.