3' splice site selection in dicot plant nuclei is position dependent

Area of Science:

• Molecular Biology
• Plant Science
• Genetics

Background:

• Plant intron recognition and splice site selection mechanisms are not well understood compared to mammalian and yeast systems.
• Plant introns exhibit less conserved splice site sequences and branchpoint sequences.
• Plant introns are enriched in adenosine and uridine residues compared to exons, potentially compensating for sequence variations.

Purpose of the Study:

• To identify critical elements for 3' splice site selection in dicotyledonous plant nuclei.
• To elucidate the role of AU-rich elements in defining intron boundaries and splice site selection.

Main Methods:

• Expression of maize Adh1 gene intron 3 in Nicotiana benthamiana nuclei using an autonomously replicating plant expression vector.
• Intron rearrangements to alter the 3' intron-exon border and assess splice site selection.
• Disruption of AU-rich elements upstream of the 3' splice site.

Main Results:

• 3' splice site selection is position-dependent.
• Cryptic 3' splice sites within the intron are masked by a functional downstream splice site.
• Multiple AU-rich elements cooperatively define the 3' intron boundary, and disruption affects selection.
• Functional 3' splice sites downstream of AU-rich sequences are preferentially selected.

Conclusions:

• AU-rich elements throughout the intron define its boundaries by creating strong AU transition points.
• These AU-rich elements play a crucial role in accurate plant pre-mRNA splicing and splice site selection.
• A model for plant intron recognition involves AU-rich elements guiding the selection of functional 3' splice sites.