The majority of plant protein-coding genes contain introns which must be removed from pre-mRNAs to produce mRNAs for translation into proteins. Introns contain conserved splicing signals which ensure fidelity of splicing.

Introns are removed in a large complex called the spliceosome. The major spliceosomal components are the U1, U2, U4/U6 and U5snRNPs (small nuclear ribonucleoprotein particles). SnRNPs contain one or two snRNAs (small nuclear RNAs) complexed with core Sm proteins and snRNP-specific proteins. In addition, a number of transiently associated proteins (for example, hnRNP and SR proteins, RNA helicases) are required for spliceosome assembly.

Plant introns differ from those of vertebrates and yeast by being U-rich, probably requiring the action of U-rich binding proteins for early recognition and spliceosome assembly.

In eukaryotes a minor spliceosome with different but related snRNAs exists to splice a minor class of introns called AT-AC introns.

Different mechanisms of splicing - intron definition and exon definition - have been proposed for plant intron removal. Splicing is an important level at which gene expression is regulated.

Alternative splicing, in particular, can give rise to functionally different protein products from the same pre-mRNA. The exon-intron structure of some pre-mRNAs require other signals to permit correct splicing (for example, inclusion of small or mini-exons).