Root hairs contribute to nutrient uptake, especially of phosphate, nitrogen and water (Olah et al., 2005). Exogenous applications of GR24 were shown to induce root hair development in Arabidopsis (Kapulnik et al., 2011). Hence we investigated the root hair system in wild‐type and PDR1 OE P. hybrida plants. PDR1 OE seedlings had longer and denser root hairs than the wild‐type, in both main and lateral roots (Fig. 7b–k). Additionally, PDR1 OE root meristems showed root hair formation closer to the main root tip (see asterisks in Fig. 7h–k). To understand whether the root hair phenotype is caused by low nutrient conditions or whether it depends on SL redistribution as a result of PDR1 overexpression, we tested root hair length under high‐ and low‐Pi conditions (see the Materials and Methods section). As expected, wild‐type P. hybrida plants had longer root hairs when grown on low Pi than on high Pi, with a significant length increase of 39.5% (Fig. S7a,b,g). pdr1 ko mutants, on the other hand, had shorter root hairs compared with the wild‐type, independent of the nutrient conditions (Fig. S7c,d,g); however, on low Pi the root hair length still increased by 28.6%. The root hairs of PDR1 OE seedlings were long on both high‐ and low‐Pi media (Fig. S7e–g), thus showing that PDR1 is a major factor determining root hair length in P. hybrida.