Isolation of a cDNA clone for a cytokinin-repressed gene in excised cucumber cotyledons

Diamonds in the rough: mRNA-like non-coding RNAs

Non-coding RNAs are increasingly being identified as crucial regulators of gene expression and other cellular functions in plants. Experimental and computational methods have revealed the existence of mRNA-like non-coding RNAs (mlncRNAs), a class of non-coding RNAs that, in plants, are associated with tissue-specific expression, development and the phosphate-starvation response. Although their mechanisms of action are largely unknown, one can speculate that mlncRNAs act through secondary structures or specific sequences that bind to proteins or metabolites, or that have catalytic activity. This review summarizes the computational methods developed to identify candidate mlncRNAs, and the current experimental evidence regarding the function of several known mlncRNAs.

Noncoding RNA for CR20, a cytokinin-repressed gene of cucumber

The CR20 gene was identified as a cytokinin-repressed gene in excised cotyledons of cucumber. We determined the sequences of some CR20 cDNAs with different structures and sequenced genomic clones for CR20. This gene consisted of three exons, and there were at least three types of transcript, which seemed to be generated by alternative splicing of the second intron. None of the CR20 transcripts included a long open reading frame (ORF). We isolated a cDNA of Arabidopsis thaliana with cucumber CR20 cDNA as a probe. This cDNA for a gene designated AtCR20-1 also lacked a long ORF. A region of 180 nucleotides was conserved in the CR20 RNA of cucumber and the AtCR20-1 RNA of Arabidopsis, although the homology was relatively low when the entire sequences were compared. Each conserved region consisted of seven elements, and seems to form stable secondary structure. These suggest that CR20 RNA may function as an RNA that is not translated into a protein.