The dwarf phenotype of theArabidopsis acl5mutant is suppressed by a mutation in an upstream ORF of a bHLH gene

Abstract

Loss-of-function mutants of the Arabidopsis thaliana ACAULIS 5 (ACL5) gene, which encodes spermine synthase, exhibit a severe dwarf phenotype. To elucidate the ACL5-mediated regulatory pathways of stem internode elongation, we isolated four suppressor of acaulis (sac) mutants that reverse the acl5 dwarf phenotype. Because these mutants do not rescue the dwarfism of known phytohormone-related mutants, the SAC genes appear to act specifically on the ACL5 pathways. We identify the gene responsible for the dominant sac51-d mutant, which almost completely suppresses the acl5 phenotype. sac51-d disrupts a short upstream open reading frame (uORF) of SAC51, which encodes a bHLH-type transcription factor. Our results indicate that premature termination of the uORF in sac51-d results in an increase in its own transcript level, probably as a result of an increased translation of the main ORF. We suggest a model in which ACL5 plays a role in the translational activation of SAC51, which may lead to the expression of a subset of genes required for stem elongation.

Global Analysis of Truncated RNA Ends Reveals New Insights into Ribosome Stalling in Plants

“…Prior to the development of Ribo-Seq, translated uORFs with regulatory functions were often identified by mutant screening or evolutionary conservation (Hill and Morris, 1993;Delbecq et al, 1994;Wiese et al, 2004;Imai et al, 2006;Hayden and Jorgensen, 2007). Although Ribo-Seq data have been used in the identification of translated uORFs (Fritsch et al, 2012;Liu et al, 2013;Ingolia et al, 2014), the application of Ribo-Seq data to the identification of ribosome stalling uORFs has not been reported.…”

Signaling and gene regulatory programs in plant vascular stem cells

“…Exogenous application of thermospermine or norspermine was able to rescue the acl5 phenotype. Furthermore, thermospermine or norspermine upregulated ATHB8, PHB, and SAC51, a gene encoding a bHLH transcription factor found from the suppressor mutant screening of acl5 (Imai et al, 2006;Kakehi et al, 2010). Based on these, thermospermine and norspermine seem to act as signaling factors for timing xylem TE differentiation program.…”

Characterization of a dehydrogenase motif and an uORF in Arabidopsis ANGUSTIFOLIA gene

“…In eukaryotes, uORFs play important roles in translational control in response to starvation and sucrose (Raney et al 2000). A number of recent studies using heterologous or modified mRNAs have indicated that uORFs can influence more than translational efficiency (Imai et al 2006;Mehta et al 2006). In this paper, we investigated the dehydrogenase activity of AN and the possible regulation of AN expression by its uORF.…”

“…In eukaryotes, uORFs have important roles in translational control in response to starvation and sucrose (Viese et al 2005;Raney et al 2000). In addition, a number of recent studies using heterologous or modified mRNAs have indicated that uORFs influence more than translational efficiency (Imai et al 2006;Mehta et al 2006). For instance, the sac51-d mutation, which involves a uORF in the bHLH-type transcription factor SAC51 gene, complements the dwarf phenotype of the Arabidopsis acl5 mutant as a result of increased SAC51 transcription (Imai et al 2006).…”

“…In addition, a number of recent studies using heterologous or modified mRNAs have indicated that uORFs influence more than translational efficiency (Imai et al 2006;Mehta et al 2006). For instance, the sac51-d mutation, which involves a uORF in the bHLH-type transcription factor SAC51 gene, complements the dwarf phenotype of the Arabidopsis acl5 mutant as a result of increased SAC51 transcription (Imai et al 2006). Thus, we cannot exclude the possibility that AN regulates its own Dehydrogenase assays were performed to measure the conversion of pyruvate to lactic acid coupled to the oxidation of NADH to NAD ϩ as described in the experimental procedures.…”