A conserved unusual posttranscriptional processing mediated by short, direct repeated (SDR) sequences in plants

In several stress responsive gene loci of monocot cereal crops, we have previously identified an unusual posttranscriptional processing mediated by paired presence of short direct repeated (SDR) sequences at 5' and 3' splicing junctions that are distinct from conventional (U2/U12-type) splicing boundaries. By using the known SDR-containing sequences as probes, 24 plant candidate genes involved in diverse functional pathways from both monocots and dicots that potentially possess SDR-mediated posttranscriptional processing were predicted in the GenBank database. The SDRs-mediated posttranscriptional processing events including cis- and trans-actions were experimentally detected in majority of the predicted candidates. Extensive sequence analysis demonstrates several types of SDR-associated splicing peculiarities including partial exon deletion, exon fragment repetition, exon fragment scrambling and trans-splicing that result in either loss of partial exon or unusual exonic sequence rearrangements within or between RNA molecules. In addition, we show that the paired presence of SDR is necessary but not sufficient in SDR-mediated splicing in transient expression and stable transformation systems. We also show prokaryote is incapable of SDR-mediated premRNA splicing.