Characterization of a negatively light-regulated mRNA from Lemna gibba

We have isolated a cDNA clone, called pLg106, which corresponds to a negatively light-regulated mRNA in the aquatic monocot Lemna gibba. Lg106 mRNA is more abundant in dark-treated plants than in plants grown under continuous white light. The levels of Lg106 mRNA reached a maximum 12-24 hours after plants had been placed in the dark. In vitro-labelled transcripts from nuclei isolated from white light-grown and darktreated Lemna hybridized equally to Lg106 DNA, indicating that transcription of the Lg106 gene was similar in both white light and darkness. Therefore, the higher level of Lg106 mRNA in the dark was not attributable to a change in transcription. We suggest that the stability of Lg106 mRNA is affected by changes in illumination. The steady-state level of Lg106 did not appear to be under phytochrome regulation, as the abundance of Lg106 mRNA from plants grown in intermittent red light or intermittent red followed immediately by far-red light was not significantly different from that of dark-treated plants. The size of the mRNA was estimated to be 650-700 nt. Genomic Southern blots indicated the presence of a single gene for Lg106. The Lg106 cDNA was sequenced and examined for similarities to nucleotide sequences in GenBank.