Characterization of the Arabidopsis Glycerophosphodiester Phosphodiesterase (GDPD) Family Reveals a Role of the Plastid‐Localized AtGDPD1 in Maintaining Cellular Phosphate Homeostasis Under Phosphate Starvation

Glycerophosphodiester phosphodiesterase (GDPD), which hydrolyzes glycerophosphodiesters intosn-glycerol-3-phosphate (G-3-P) and the corresponding alcohols, plays an important role in various physiological processes in both prokaryotes and eukaryotes. However, little is known about the physiological significance of GDPD in plants. Here, we characterized the Arabidopsis GDPD family that can be classified into canonical GDPD (AtGDPD1-6) and GDPD-like (AtGDPDL1-7) subfamilies.In vitro analysis of enzymatic activities showed that AtGDPD1 and AtGDPDL1 hydrolyzed glycerolphosphoglycerol, glycerophosphocholine and glycerophospho-ethanolamine, but the maximum activity of AtGDPD1 was much higher than that of AtGDPDL1 under our assay conditions. Analyses of gene expression patterns revealed that all AtGDPD genes except for AtGDPD4 were transcriptionally active in flowers and siliques. In addition, the gene family displayed overlapping and yet distinguishable patterns of expression in roots, leaves and stems, indicating functional redundancy as well as specificity of GDPDgenes. At GDPDs but not AtGDPDLs are up-regulated by inorganic phosphate (Pi)starvation. Loss-of-function of the plastid-localized AtGDPD1 leads to a significant decrease in GDPD activity,G-3-P content, Picontent and seedling growth rate only under Pistarvation compared with the wild type (WT).However, membrane lipid compositions in the Pi-deprived seedlings remain unaltered between the AtGDPD1 knockout mutant and WT. Thus, we suggest that the GDPD-mediated lipid metabolic pathway may be involved in release of Pifrom phospholipids during Pistarvation.