Defense-related callose synthasePMR4promotes root hair callose deposition and adaptation to phosphate deficiency inArabidopsis thaliana

Abstract

SummaryPlants acquire phosphorus (P) primarily as inorganic phosphate (Pi) from the soil. Under Pi deficiency, plants induce an array of physiological and morphological responses, termed phosphate starvation responses (PSR), thereby increasing Pi acquisition and use efficiency. However, the mechanisms underlying and finetuning PSR remain to be elucidated. Here, we report that deposition of a β-1,3-glucan polymer called callose is induced inArabidopsis thalianaroot hairs under Pi deficiency, in a manner independent ofPHR1/PHL1transcription factors andLPR1/LPR2ferroxidases, mediating systemic and local PSR, respectively. A mutagenic screen has revealedPMR4(GSL5) callose synthase being required for the callose deposition under Pi deficiency. Loss ofPMR4also affects different PSR-characteristic outputs, including phosphate mobilization, plant growth and anthocyanin accumulation, indicating a critical role forPMR4-dependent callose in PSR. The PSR defects are not affected by simultaneous disruption ofSID2, mediating defense-associated salicylic acid (SA) biosynthesis, unlike SA-dependent powdery mildew resistance previously described inpmr4. Grafting analyses and genetic studies on root hair-defective mutants suggest thatPMR4-dependent callose deposition in the root hairs contributes to shoot Pi accumulation during PSR. Our findings thus illuminate an important role forPMR4in plant adaptation to Pi deficiency.