title: Signaling of phosphorus deficiency-induced gene expression in white lupin requires sugar and phloem transport.
abstract: Roots of phosphorus (P)-deficient white lupin exhibit striking changes in morphology and gene expression. In this report we provide further insight into genetic elements affecting transcription of P-deficiency-induced genes. Moreover, we also show that sugars and photosynthates are integrally related to P-deficiency-induced gene expression. White lupin phosphate transporter (LaPT1) and secreted acid phosphatase (LaSAP1) promoter-reporter genes when transformed into alfalfa, a heterologous legume, showed significant induction in roots specifically in response to P-deficiency. In addition, both promoters were active in nitrogen-fixing root nodules but not in ineffective nodules indicating a link between P-deficiency and factors related to nitrogen fixation/metabolism. As sugars play a role in signal transduction during nitrogen assimilation and are required for effective nitrogen fixation, we tested the relationship of sugars to P-deficiency-induced gene expression. Exogenous sucrose, glucose, and fructose stimulated LaPT1 and LaSAP1 transcript accumulation in dark-grown P-sufficient white lupin seedlings. Furthermore, in intact P-deficient white lupin plants, LaPT1 and LaSAP1 expression in cluster roots was strikingly reduced in dark-adapted plants with expression rapidly restored upon reexposure to light. Likewise, interruption of phloem supply to P-deficient roots resulted in a rapid decline in LaPT1 and LaSAP1 transcript accumulation. Similar results were also obtained with a third lupin P-deficiency-induced gene encoding a putative multidrug and toxin efflux protein (LaMATE). Taken together, our data show that the regulation of P-deficiency-induced genes is conserved across plant species and sugars/photosynthates are crucial for P-deficiency signal transduction.
authors.affiliation: Agronomy and Plant Genetics, University of Minnesota, St Paul, MN 55108, USA. liuxx162@tc.umn.edu
authors.forename: Junqi
authors.initials: J
authors.lastname: Liu
authors.forename: Deborah A
authors.initials: DA
authors.lastname: Samac
authors.forename: Bruna
authors.initials: B
authors.lastname: Bucciarelli
authors.forename: Deborah L
authors.initials: DL
authors.lastname: Allan
authors.forename: Carroll P
authors.initials: CP
authors.lastname: Vance
mesh_terms: D001692:Biological Transport; D050260:Carbohydrate Metabolism; D015870:Gene Expression; D018506:Gene Expression Regulation, Plant; D017930:Genes, Reporter; D031297:Lupinus; D000455:Medicago sativa / Q000235:genetics*; D010758:Phosphorus / Q000172:deficiency*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic; D011506:Proteins / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D010940:Plant Proteins; D011506:Proteins; D010758:Phosphorus