A New Member of the CtBP/BARS

Abstract

The ANGUSTIFOLIA (AN) gene in Arabidopsis thaliana (L.) Heynh. is the first homolog of the CtBP/BARS gene family identified in plants and is responsible for the polarity-dependent control of leaf cell expansion. This review compares the sequence homology and functional similarity of the AN protein with authentic animal CtBP/BARS family proteins. AN homologs have been found in both angiosperms and mosses, suggesting AN is conserved in terrestrial plant genomes. The AN subfamily is unique in having not only the D-isomer-specific 2-hydroxy acid dehydrogenase (D2-HDH) motif that is conserved among the CtBP/BARS family but also putative LxCxE/D and nuclear localization signal (NLS) motifs and a long C-terminal region. The absence of the catalytic triad, which is conserved in all D2-HDH sequences and is believed to be essential for the corepression activity of CtBP, suggests that AN might differ, at least in part, from CtBPs in molecular function. In addition, the distribution and density of the Golgi apparatus is normal in a null allele of the an mutant, suggesting that AN might not have a BARS function. An analysis of cytoskeletons in an mutant leaf cells suggests that AN might play an important role in controlling the arrangement of cortical microtubules that is plant-specific cytoskeletons. With all these attributes, AN appears to be the third member of an enigmatic family, CBA = CtBP/BARS/AN, which regulates aspects of developmental and organelle control in animals and plants.