A cold-inducible bZIP protein gene in radish root regulated by calcium- and cycloheximide-mediated signals

Abstract

To study molecular events at low temperatures, we cloned a cDNA encoding a low temperature-induced basic region/leucine zipper protein termed rd lip from radish roots. The rd lip was encoded by a single-copy gene belonging to the lip gene family that seems to act as a transcription factor. Levels of rd lip transcript were up-regulated by low temperature, drought stress and abscisic acid, but remained unchanged by high temperature and salt stresses. Ionomycin, an ionophore that increases calcium flow into the cytoplasm, was also shown to stimulate the accumulation of rd lip transcripts. Further, expression analyses of rd lip mRNA showed that the expression was induced in roots either with low (0.1 μM) or high (100 μM) concentrations of cycloheximide. Induction by low temperature was restricted to the middle part of the roots, while induction by low and high concentrations of cycloheximide occurred at the root tip and the upper part of the roots, respectively. Thus, our results suggest that cold-inducible rd lip gene activation is regulated by calcium- and cycloheximide-mediated signals in radish roots.