Genome accessibility dynamics in response to phosphate limitation is controlled by the PHR1 family of transcription factors in Arabidopsis

As phosphorus is one of the most limiting nutrients in many natural and agricultural ecosystems, plants have evolved strategies that cope with its scarcity. Genetic approaches have facilitated the identification of several molecular elements that regulate the phosphate (Pi) starvation response (PSR) of plants, including the master regulator of the transcriptional response to phosphate starvation PHOSPHATE STARVATION RESPONSE1 (PHR1). However, the chromatin modifications underlying the plant transcriptional response to phosphate scarcity remain largely unknown. Here, we present a detailed analysis of changes in chromatin accessibility during phosphate starvation in Arabidopsis thaliana root cells. Root cells undergo a genome-wide remodeling of chromatin accessibility in response to Pi starvation that is often associated with changes in the transcription of neighboring genes. Analysis of chromatin accessibility in the phr1 phl2 double mutant revealed that the transcription factors PHR1 and PHL2 play a key role in remodeling chromatin accessibility in response to Pi limitation. We also discovered that PHR1 and PHL2 play an important role in determining chromatin accessibility and the associated transcription of many genes under optimal Pi conditions, including genes involved in the PSR. We propose that a set of transcription factors directly activated by PHR1 in Pi-starved root cells trigger a second wave of epigenetic changes required for the transcriptional activation of the complete set of low-Pi-responsive genes.