Isolation and expression of an elongation-dependent gene of mung bean (Vigna radiata) hypocotyl

A cDNA clone of an auxin up-regulated gene, ARG8, was isolated from hypocotyl sections of etiolated mung bean [Vigna radiata (L.) Wilczek] seedlings by differential screening, The deduced amino acid sequence suggested that ARG8 may encode a cel wall protein, The steady state mRNA level of ARG8 increased by treatment of hypocotyl sections not only with indole-3-acetic acid (IAA) but also with fusicoccin, and the auxin inducibility was inhibited by the addition of 0.3 M mannitol in the incubation medium. This indicated that it was not auxin but elongation that regulated the expression of ARG8. The promoter activity of the 5'-flanking region of ARG8 was determined by assaying the transient expression of a luciferase fusion gene that was introduced into mung bean hypocotyl sections by the particle bombardment technique. The basal activity of the ARG8 upstream region was about a few tenths of that of a modified cauliflower mosaic virus 35S promoter, and it was increased a few fold by treatment with IAA. The auxin inducibility was completely suppressed by the addition of mannitol, A 5'-deletion analysis showed that a 53-bp region in the ARG8 promoter was important for the basal and elongation-dependent promoter activities.