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

Abstract

ANGUSTIFOLIA (AN), the first gene encoding a putative C-terminal binding protein (CtBP) identified in plants, controls leaf cell width in a polarity-dependent manner by regulating the arrangement of cortical microtubules. However, several differences in the sequence of AN have been detected in its conserved CtBP domains, which are transcriptional co-repressors in animals; thus, it is unclear whether AN is a transcriptional co-repressor in plants and how it may function. In this study, we found that AN possesses incomplete D2-HDH and GxGxxG(17x)D motifs, which confer CtBP dehydrogenase activity and NAD-binding for interaction with PxDLS motifs, respectively. In addition, full-length AN was unable to couple the reduction of pyruvate to lactic acid with the oxidation of NADH to NAD+, suggesting that it might not have dehydrogenase activity. Moreover, we found that AN has an additional short open reading frame (ORF), which was identified as an upstream ORF (uORF), in its 5′-untranslated region that overlaps with the start codon of the AN gene. Transcriptional analysis revealed that the uORF and AN ORF are transcribed as a single molecule, indicating that the uORF might influence AN transcription during leaf development.