Splicing of precursors to mRNA in higher plants: mechanism, regulation and sub-nuclear organisation of the spliceosomal machinery.

摘要

The removal of introns from pre-mRNA transcripts and the concomitant ligation of exons is known as pre-mRNA splicing, which is a fundamental aspect of constitutive eukaryotic gene expression and an important level at which gene expression is regulated. The mechanism and regulation of pre-mRNA splicing in higher plants, and the sub-nuclear organization of the spliceosomal machinery, are reviewed in this paper. Heterologous introns are often not processed in higher plants indicating that, although highly conserved, the process of pre-mRNA splicing in plants exhibits significant differences that distinguish it from splicing in yeast and mammals. A fundamental distinguishing feature is the presence of and requirement for AU or U-rich intron sequence in higher-plant pre-mRNA splicing. This review documents the properties of higher-plant introns and trans-acting spliceosomal components and also discusses the means by which these elements combine to determine the accuracy and efficiency of pre-mRNA processing. Examples of how introns can effect regulated gene expression by affecting the nature and abundance of mRNA in plants are detailed and the effects of environmental stresses on splicing are listed. Spliceosomal components exhibit a distinct patternof organization in higher-plant nuclei. Effective probes that reveal this pattern have only recently become available, but the domains in which spliceosomal components concentrate were identified in plant nuclei as enigmatic structures some sixty yearsago. The organization of spliceosomal components in plant nuclei is reviewed and these recent observations are unified with previous cytochemical and ultrastructural studies of plant ribonucleoprotein domains.