Arabidopsis thaliana AUCSIA-1 regulates auxin biology and physically interacts with a kinesin-related protein.

Aucsia is a green plant gene family encoding 44–54 amino acids long miniproteins. The sequenced genomes of most landplants contain two Aucsia genes. RNA interference of both tomato (Solanum lycopersicum) Aucsia genes (SlAucsia-1 andSlAucsia-2) altered auxin sensitivity, auxin transport and distribution; it caused parthenocarpic development of the fruit andother auxin-related morphological changes. Here we present data showing that the Aucsia-1 gene of Arabidopsis thalianaalters, by itself, root auxin biology and that the AtAUCSIA-1 miniprotein physically interacts with a kinesin-related protein.The AtAucsia-1 gene is ubiquitously expressed, although its expression is higher in roots and inflorescences in comparisonto stems and leaves. Two allelic mutants for AtAucsia-1 gene did not display visible root morphological alterations; howeverboth basipetal and acropetal indole-3-acetic acid (IAA) root transport was reduced as compared with wild-type plants. Thetranscript steady state levels of the auxin efflux transporters ATP BINDING CASSETTE subfamily B (ABCB) ABCB1, ABCB4 andABCB19 were reduced in ataucsia-1 plants. In ataucsia-1 mutant, lateral root growth showed an altered response to i)exogenous auxin, ii) an inhibitor of polar auxin transport and iii) ethylene. Overexpression of AtAucsia-1 inhibited primaryroot growth. In vitro and in vivo protein-protein interaction experiments showed that AtAUCSIA-1 interacts with a 185 aminoacids long fragment belonging to a 2712 amino acids long protein of unknown function (At4g31570). Bioinformatics analysisindicates that the AtAUCSIA-1 interacting protein (AtAUCSIA-1IP) clusters with a group of CENP-E kinesin-related proteins.Gene ontology predictions for the two proteins are consistent with the hypothesis that the AtAUCSIA-1/AtAUCSIA-1IPcomplex is involved in the regulation of the cytoskeleton dynamics underlying auxin biology.