A Glycine-Rich Protein Encoded by Sulfur-Deficiency Induced Gene Is Involved in the Regulation of Callose Level and Root Elongation

Abstract

Glycine-rich proteins (GRPs) with characteristic repetitive glycine stretches are ubiquitous in organisms of all Kingdoms and have distinct functions. It is believed that Gly-rich domains serve mainly for interactions with other proteins. Previously, we identified the tobacco UP30 gene as strongly upregulated by sulfur deficiency. It encodes a protein highly similar to cdiGRP which affects tobacco defense response by elevating cell wall callose deposits thus blocking systemic movement of viruses. The closest Arabidopsis thaliana homologue of UP30 is GRP-3 (At2g05520). Here we report that GRP-3 is induced in Arabidopsis seedlings in both sulfur and nitrogen deficiency conditions. The transgenic Arabidopsis plants with changed GRP-3 expression (either overexpressing or with silenced GRP-3) tend to have longer roots than the wild type, especially in the conditions of sulfur deficiency. The effect could be alleviated by the addition of auxin to the media. Moreover, we observed the increased callose deposition in both Arabidopsis lines suggesting its negative effects on shoot-to-root movement of auxins in nutrient deficient conditions.