Differential requirement for the function of SRD2, an snRNA transcription activator, in various stages of plant development.

Small nuclear RNA (snRNA) is a class of eukaryotic noncoding RNAs, which have essential roles in pre-mRNA splicing and rRNA processing. As these functions are fundamental to cell activities, the regulation of snRNA transcription should be a vital issue for all eukaryotes. Here we address developmental control of snRNA transcription and its significance through the analysis of the SRD2 gene of Arabidopsis (Arabidopsis thaliana), which encodes an activator of snRNA transcription. In young seedlings, a high level of SRD2 expression was observed in shoot and root apical meristems, leaf primordia, and root stele tissues, where a large amount of snRNA accumulated. In mature plants, SRD2 was highly expressed in developing leaves and flowers as well as apical meristems. Mutations in the SRD2 gene interfered with many, but not all, aspects of development in the regions that showed strong expression of SRD2. Of note, establishment of the fully active state of apical meristems in the seedling stage was very sensitive to the srd2-1 mutation, while maintenance of the established meristems was substantially insensitive. These results demonstrated differential requirement for the SRD2 function in various stages of plant development.