Summary Root hair development is crucial for phosphate absorption, but how phosphorus deficiency affects root hair initiation and elongation remains unclear. We demonstrated the roles of auxin efflux carrier PIN‐FORMED2 (PIN2) and phospholipase D (PLD)‐derived phosphatidic acid (PA), a key signaling molecule, in promoting root hair development in Arabidopsis thaliana under a low phosphate (LP) condition. Root hair elongation under LP conditions was greatly suppressed in pin2 mutant or under treatment with a PLDζ2‐specific inhibitor, revealing that PIN2 and polar auxin transport and PLDζ2‐PA are crucial in LP responses. PIN2 was accumulated and degraded in the vacuole under a normal phosphate (NP) condition, whereas its vacuolar accumulation was suppressed under the LP or NP plus PA conditions. Vacuolar accumulation of PIN2 was increased in pldζ2 mutants under LP conditions. Increased or decreased PIN2 vacuolar accumulation is not observed in sorting nexin1 (snx1) mutant, indicating that vacuolar accumulation of PIN2 is mediated by SNX1 and the relevant trafficking process. PA binds to SNX1 and promotes its accumulation at the plasma membrane, especially under LP conditions, and hence promotes root hair development by suppressing the vacuolar degradation of PIN2. We uncovered a link between PLD‐derived PA and SNX1‐dependent vacuolar degradation of PIN2 in regulating root hair development under phosphorus deficiency.

Pollination limitation is common in flowering plants and is thought to be a factor driving the evolution of floral traits. The plasticity of floral longevity to pollination may be an adaptation of plants to pollen limitation. However, this adaptation is less critical in short‐lived flowers. To evaluate pollen limitation and the plasticity of floral longevity to pollination in Potentilla tanacetifolia, a gynodioecious herb with short‐lived flowers, we analyzed its breeding system, tested sex‐differential pollen limitation, and compared variations in floral display size in natural populations in Duolun County, Inner Mongolia, China. Hand pollination experiments and pollinator exclusion treatments revealed that P. tanacetifolia is self‐compatible and non‐autonomously apomictic and shows sex‐differential pollen limitation. The plasticity of floral longevity to pollination was observed; the floral duration of female plants was prolonged by approximately 3–4 hours with pollination exclusion treatment. Moreover, the percentage of flowers displayed on female plants during pollination exclusion treatment was significantly higher than that during natural pollination. Under natural pollination conditions, the percentage of flowers displayed on female plants was significantly higher than on hermaphrodite plants. Furthermore, approximately 50% of the pollen grains spread out of the anthers of hermaphrodite flowers within 2 h of anthesis; the number of pollen grains adhering to the stigmas of hermaphrodite flowers was significantly higher than that adhering to female flowers when flowers shed their petals. These results indicate that variation in floral longevity may be an adaptive strategy to pollination conditions for gynodioecious P. tanacetifolia.