Major latex-like proteins identified from Cucurbita pepo control primary root elongation

Major latex-like proteins (MLPs) play a crucial role in the accumulation of hydrophobic organic pollutants in the Cucurbitaceae family. MLPs bind to hydrophobic organic pollutants in roots, and their complexes are secreted into xylem vessels. Consequently, hydrophobic organic pollutants are transported to the aerial parts. MLP-PG1 and MLP-GR3 serve as transporting factors for hydrophobic organic pollutants in zucchini (Cucurbita pepo) and are highly expressed in the roots. However, the biological functions of these MLPs in the roots remain elusive. In the current study, we show that MLP-PG1 and MLP-GR3 control primary root elongation. We found that both MLP-PG1 and MLP-GR3 bound to indole-3-acetic acid (IAA) in vitro. Primary root elongation was suppressed in the transgenic tobacco plants overexpressing MLP-PG1 and MLP-GR3, while it was promoted in one of the Arabidopsis thaliana mlp mutants. Furthermore, these MLPs did not influence the endogenous IAA content. These results suggest that MLPs control primary root elongation by inactivating IAA in the roots.