A mutant isolated from a screen of EMS-mutagenized Arabidopsis lines,per1,showed normal root hair development under control conditions but displayed an inhibited root hair elongation phenotype upon Pi deficiency.Additionally,the per1 mutant exhibited a pleiotropic phenotype under control conditions,resembling Pi-deficient plants in several aspects.Inhibition of root hair elongation upon growth on low Pi media was reverted by treatment with the Pi analog phosphite,suggesting that the mutant phenotype is not caused by a lack of Pi.Reciprocal grafting experiments revealed that the mutant rootstock is sufficient to cause the phenotype.Complementation analyses showed that the PER1 gene encodes an ubiquitin-specific protease,UBP14.The mutation caused a synonymous substitution in the 12th exon of this gene,resulting in a lower abundance of the UBP14 protein,probably as a consequence of reduced translation efficiency.Transcriptional profiling of per1 and wild-type plants subjected to short-term Pi starvation revealed genes that may be important for the signaling of Pi deficiency.We conclude that UBP14 function is crucial for adapting root development to the prevailing local availability of phosphate.
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