alpha 2-COP is involved in early secretory traffic in Arabidopsis and is required for plant growth

Abstract

[EN] COP (coat protein) I-coated vesicles mediate intra-Golgi transport and retrograde transport from the Golgi to the endoplasmic reticulum. These vesicles form through the action of the small GTPase ADP-ribosylation factor 1 (ARF1) and the COPI heptameric protein complex (coatomer), which consists of seven subunits (alpha-, beta-, beta' -, gamma-, delta-, epsilon- and xi-COP). In contrast to mammals and yeast, several isoforms for coatomer subunits, with the exception of gamma and delta, have been identified in Arabidopsis. To understand the role of COPI proteins in plant biology, we have identified and characterized a loss-of-function mutant of alpha 2-COP, an Arabidopsis alpha-COP isoform. The alpha 2-cop mutant displayed defects in plant growth, including small rosettes, stems and roots and mislocalization of p24 delta 5, a protein of the p24 family containing a C-terminal dilysine motif involved in COPI binding. The alpha 2-cop mutant also exhibited abnormal morphology of the Golgi apparatus. Global expression analysis of the alpha 2-cop mutant revealed altered expression of plant cell wall-associated genes. In addition, a strong upregulation of SEC31A, which encodes a subunit of the COPII coat, was observed in the alpha 2-cop mutant; this also occurs in a mutant of a gene upstream of COPI assembly, GNL1, which encodes an ARF-guanine nucleotide exchange factor (GEF). These findings suggest that loss of alpha 2-COP affects the expression of secretory pathway genes.