NUCLEAR PRE-MESSENGER-RNA PROCESSING IN HIGHER-PLANTS

This chapter focuses on nuclear pre-mRNA splicing in plants, with emphasis on maize. It discusses the salient points of nuclear intron splicing in yeast and animals. Then it reviews the literature on small nuclear RNAs and plant intron splicing, and present a working model for plant intron recognition. It also evaluates the alternative RNA processing events for several transposable-element-induced mutations of maize as a test of the intron recognition model. Introns are included in the primary transcript (pre-mRNA), but are excised in the nucleus before the mature mRNA is translated into protein. Plant internal introns (within coding regions) average only 249 nt versus 1127 nt for vertebrates and 86 nt for fungi. Furthermore, for example, 80% of all maize introns are less than 200 nt. Plant introns are thus more like introns from other lower eukaryotes (e. g.,Tetrahymena, Caenohrabditis), which are also short. Results from experiments using synthetic introns indicate that a minimum intron length of 70-73 nt is necessary for efficient splicing in both monocots and dicots. This is consistent with the size distribution of natural introns; for example, only 3% of maize introns are less than 73 nt. The minimum size of plant introns is similar to the minimum length of -80 nt required for efficient splicing in mammals. © 1994, Academic Press Inc.