The cell morphogenesis gene ANGUSTIFOLIA encodes a CtBP/BARS-like protein and is involved in the control of the microtubule cytoskeleton

The ANGUSTIFOLIA (AN) gene is required for leaf hair (trichome) branching and is also involved in polarized expansion underlying organ shape. Here we show that the AN gene encodes a C-terminal binding proteins/brefeldin A ADP-ribosylated substrates (CtBP/BARS) related protein. AN is expressed at low levels in all organs and the AN protein is localized in the cytoplasm. In an mutant trichomes, the organization of the actin cytoskeleton is normal but the distribution of microtubules is aberrant. A role of AN in the control of the microtubule cytoskeleton is further supported by the finding that AN genetically and physically interacts with ZWICHEL, a kinesin motor molecule involved in trichome branching. Our data suggest that CtBP/BARS-like protein function in plants is directly associated with the microtubule cytoskeleton.     

Characterization of a member of the AN subfamily, IAN, from Ipomoea nil

ANGUSTIFOLIA (AN) is the first C-terminal binding protein (CtBP) gene from plants and controls leaf width and pattern of trichome branching in Arabidopsis thaliana (L.) Heynh. We characterized an ortholog of AN from Ipomoea nil (L.) Roth (Japanese morning glory) and designated it Ipomoea nil's AN (IAN). IAN is a single-copy gene in the genome and is expressed ubiquitously in various organs of I. nil. IAN contains not only a D2-HDH motif, which is highly conserved within the CtBP family, but also LXCXE, NLS and PEST motifs, which are specific to the AN subfamily. The expression of IAN cDNA driven by the cauliflower mosaic virus 35S promoter restored a defect in leaf expansion in the leaf width direction in the angustifolia-1 (an-1) mutant of Arabidopsis, suggesting that IAN retains a common function with AN. In contrast, the complementation by IAN of a defect in the trichome branching pattern on the leaf surface of the an-1 mutant was less effective than that observed for leaf shape. These results suggest that the mechanisms by which AN regulates leaf width and trichome branching are separable.