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Plant Cell, Vol. 10, 1465-1478, September 1998, Copyright © 1998, American Society of Plant Physiologists
An Intragenic Suppressor of the Arabidopsis Floral Organ Identity Mutant apetala3-1 Functions by Suppressing Defects in Splicing
Ying Yia and
Thomas Jacka
a Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755
Correspondence to:
Thomas Jack, thomas.jack{at}dartmouth.edu (E-mail), 603-646-1347 (fax).
The Arabidopsis floral organ identity gene APETALA3 (AP3) specifies the identity of petals and stamens in the flower. In flowers mutant for the temperature-sensitive ap3-1 allele, the petals and stamens are partially converted to sepals and carpels, respectively. ap3-1 contains a single nucleotide change in the AP3 gene that alters both an amino acid in the AP3 protein and the 5' splice consensus site for intron 5. Surprisingly, the Ap3-1 mutant phenotype is not due to the missense mutation but instead is due to defects in splicing; specifically, exon 5 is frequently skipped by the splicing machinery at the restrictive temperature. In a screen for suppressors of ap3-1, we isolated an intragenic suppressor, ap3-11, that functions to suppress the splicing defects of ap3-1. Using a reverse transcriptasepolymerase chain reaction assay, we demonstrate that the percentage of full-length exon 5containing AP3 RNAs correlates with the phenotype of the flowers in both ap3-1 and ap3-11. Rather surprisingly, the ap3-11 suppressor mutation is located in intron 4. One model explaining the function of ap3-11 is that the ap3-11 suppressor creates a novel branch point sequence that causes exon 5 to be more frequently recognized by the splicing machinery. The identification of such a suppressor strongly suggests that exon-scanning models of intronexon recognition are operative in plants.
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