Suppression of the dwarf phenotype of an Arabidopsis mutant defective in thermospermine biosynthesis by a synonymous codon change in the SAC51 uORF.

Thermospermine plays a critical role in negatively regulating xylem development in angiosperms. A mutant of Arabidopsis thaliana that is defective in thermospermine biosynthesis, acaulis5 (acl5), exhibits a dwarf phenotype with excessive xylem formation. Mechanistically thermospermine acts in attenuating the inhibitory effect of an evolutionarily conserved upstream open reading frame (uORF) on the main ORF of SAC51, which encodes a basic helix-loop-helix protein involved in xylem repression. Here, we revealed that a semidominant suppressor of acl5, sac503, which partially restores the acl5 phenotype, has a point mutation in the conserved uORF of SAC51 with no amino acid substitution in the deduced peptide sequence. In transgenic lines carrying the ß-glucuronidase (GUS) reporter gene fused with the SAC51 5' region containing the uORF, the mutant construct was shown to confer higher GUS activity than does the wild-type SAC51 construct. We confirmed that sac503 mRNA was more stable than SAC51 mRNA in acl5. These results suggest that the single-base change in sac503 positively affects the translation of its main ORF instead of thermospermine. We further found that the uORF-GUS fusion protein could be synthesized in planta from the wild-type and sac503 translational fusion constructs.

Easy-to-Use InDel Markers for Genetic Mapping between Col-0 and Ler-0 Accessions of Arabidopsis thaliana.

Map-based gene cloning has played a key role in many genetic studies using the model plant, Arabidopsis thaliana. In the post- next generation sequencing era, identification of point mutations and their corresponding genes is increasingly becoming a powerful and important approach to define plant gene function. To perform initial mapping experiments efficiently on Arabidopsis mutants, enrichment of easy-to-use and reliable polymorphic DNA markers would be desirable. We present here a list of InDel polymorphic markers between Col-0 and Ler-0 accessions that can be detected in standard agarose gel electrophoresis.