El gen de Arabidopsis PHR2 (Phosphate Starvation Response 2)codifica una proteína de retículo endoplásmico involucrada en el tráfico de transportadores de fosfato de alta afinidad a la membrana plasmática

Abstract

Plants have evolved responses to adapt their growth to conditions of limited inorganic phosphate (Pi) supply, one of whose hallmarks is the activation of high affinity Pi transporters. The MYB transcription activator PHOSPHATE STARVATION RESPONSE 1 (PHRI) is an important component in the regulation of these responses. In this study, we isolated PHR2 whose mutation results in the constitutive expression of many Pi starvation induced genes and in reduced Pi accumulation, while responses to other types of nutrient starvation stresses remain mostly unaffected. PHR2 encodes a plant specific SEC12-related protein, although it lacks some presumably relevant conserved residues in known SEC12 proteins, and is itself induced by phosphate starvation and to a lesser extent during senescence, another Pi mobilizing condition. Studies with an active PHR2:GFP fusion protein showed that it is localized in the endoplasmic reticulum (ER), like other SEC12 proteins. We found that phr2 impairs the plasmamembrane localization of the PHT1;l phosphate transporter, which accumulates in the ER of mutant plants. In contrast, the activity of several Pi stawation phosphatases and RNAses is not decreased in the mutant, raising the possibility of a plant specific posttranslational control mechanism of Pi uptake.