The histone deacetylase HDA19 controls root cell elongation and modulates a subset of phosphate starvation responses in Arabidopsis

The length of root epidermal cells and their patterning into files of hair-bearing and non-hair cells are genetically determined but respond with high plasticity to environmental cues. Limited phyto-availability of the essential mineral nutrient phosphate (Pi) increases the number of root hairs by longitudinal shortening of epidermal cells and by reprogramming the fate of cells in positions normally occupied by non-hair cells. Through analysis of the root morphology and transcriptional profiles from transgenic Arabidopsis lines with altered expression of the histone deacetylase HDA19, we show that in an intricate interplay of Pi availability and intrinsic factors, HDA19 controls the epidermal cell length, probably by altering the positional bias that dictates epidermal patterning. In addition, HDA19 regulates several Pi-responsive genes that encode proteins with important regulatory or metabolic roles in the acclimation to Pi deficiency. In particular, HDA19 affects genes encoding SPX (SYG1/Pho81/XPR) domain-containing proteins and genes involved in membrane lipid remodeling, a key response to Pi starvation that increases the free Pi in plants. Our data add a novel, non-transcriptionally regulated component of the Pi signaling network and emphasize the importance of reversible post-translational histone modification for the integration of external signals into intrinsic developmental and metabolic programs.