RAGHOTHAMA, K. G.

VASCONCELOS, M. J. V. D.

VASCONCELOS, M. J. V. de

Repository Open Access to Scientific Information from Embrapa

P-758PAG-XVI Plant & Animal Genomes Conference - San Diego, California on January 12-16,2008Molecular analyses of glycerol-3-phosphate permease - G3P genes induced by phosphatestress in maizeVasconcelos, M.J.l; Raghothama K. G. 2lEmbrapa Maize and Sorghum, PO box151, Sete Lagoas, MG, Brazil, 35701-9702Department ofHorticulture and Landscape Architecture, Purdue University, WestLafayette-IN 47907Many essential biological processes are carried out inside sub-cellular compartments suchas plastids and mitochondria. These pathways often require an extensive transport mediatedexchange of metabolites between compartments and surrounding cytosol. At some pointalmost all these processes require phosphate. Phosphate shortage may adversely affecttransport across the membranes ofthese isolated compartments. The impact ofPi starvationmay be more severe in compartments such as chloroplasts that are actively exportingorganic-P metabolites in exchange for inorganic phosphorus. Chloroplasts, utilize a varietyof sugar transporters to maintain normal biological activities. Interestingly, many of theseare antiporters that couple the efflux transport of a sugar-phosphate to the influx of PioAmong these include a hexose transporter that exports the products of starch degradationfrom the plastids, an ADP/ATP transporter that supplies plastids with energy forbiosynthesis of a wide variety of compounds transporters belonging to the major facilitatorsuperfamily (MFS) which function as antiporters exchanging Pi for C3 and C6 compounds.G3P, the topic of this study, is also a member of MSF. G3P is strongly induced underphosphate deficiency in maize. These genes exhibit temporal, spatial and phosphatedeficiency associated patterns of expression. Although there were differences in theexpression of phosphate starvation induced genes, no consistent pattem of expressionassociated with either phosphate efficient or inefficient genotypes of maize emerged. Itappears that phosphate efficiency in maize is a complex trait mediated by coordinatedaction of groups of genes either induced or suppressed in response to nutrient deficiency ..

Molecular analyses of glycerol-3-phosphate permease - G3P genes induced by phosphate stress in maize.

Molecular Analyses of Glycerol-3- Phosphate Permease-G3 PGenes Induced by Phosphate Stress in MaizeMJ Vasconcelos 1 • and KG Raghothama'1. Embrapa Maize and Sorghum, PO Box151, Sete Lagoas, MG, Brazil, 35701-970.2. Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette-Ilv 47907, USA.* Corresponding author , mjose@ cnpms. embrapa. brABSTRACTMany essential biological processes are carried out inside sub-cellular compartments such as plastids and mitochondria. Atsome points almost all these processes require phosphorus (P). The impact of Pi starvation may be more severe in compartmentssuch as chloroplasts that are actively exporting organic-P metabolites in exchange for inorganic P. Transporters that exportproducts and supplies plastids with energy for biosynthesis including starch and fatty acids, and sugar transporters belonging tothe major facilitator superfamily (MFS). Glycerol-3-phosphate permease (G3P), the topic of this study, is also a member ofMSF. G3P is strongly induced under phosphate deficiency in maize.INTRODUCTIONMany essential biological processes are carried outinside sub-cellular compartments such as plastids andmitochondria. These pathways often require an extensivetransport mediated exchange of metabolites betweencompartments and surrounding cytosol (Eicks et aI.,2002). At some points almost a11these processes require Peither as orthophosphate or in the organic formo Phosphateshortage may adversely affect transport across the membranesof these isolated compartments. The impact of Pi starvationmay be more severe in compartments such as chloroplaststhat are actively exporting organic-P metabolites in exchangefor inorganic phosphorus. Plastids, like chloroplasts, utilizea variety of sugar transporters to maintain normal biologicalactivities. Interestingly, many of these are antiporters thatcouple the efflux transport of a sugar-phosphate to the influxof Pi (Streatfield et al. , 1999). Among these include ahexose transporter that exports the products of starchdegradation from the plastids (W eber et al, , 2000), anADP/ ATP transporter that supplies plastids with energy forbiosynthesis of a wide variety of compounds including starchand fatty acids (Neuhaus et al., 1997), and sugartransporters belonging to the major facilitator superfamily( MFS) which function as antiporters exchanging Pi for C3and C6 compounds (Griffith et al. , 1992). Glycerol-3-phosphate permease, the topic of this study, is also amember of MSF.MATERIALS AND METHODSThe genotypes of Zea mays (L ) were selected basedon their response to and utilization of applied Pio Thesegenotypes were developed at Embrapa maize and sorghum,Brazil, through selection and conventional breeding. Thesegenotypes were classified mainly into two categories namelyefficient and inefficient types based on their yield potentials.Seeds of maize were germinated in seedling trayscontaining Scott's ready earth plug mix (Scotts Co.,Marysville, OH) and grown in the greenhouse for one week.One-week-old seedlings were gently washed with water toremove the soil medium off the roots. Seedlings were thentransferred to one half-strength modified Hoagland's nutrientsolution (Liu et aI. , 1998b). Mter one week, plants wereagain transferred to Hoagland nutrition solution containingdifferent concentrations of Pi (O, 5, 10, 25, 50, 100 and250 IJ.M). During the course of the treatments, nutrientssolutions were renewed on altemate days. After 15 days oftreatment , roots were harvested from plants grown underdifferent Pi concentrations, frozen in liquid nitrogen andRNA was extracted for Northem analysis. Since theevaluation of the expression of different phosphatetransporters in maize revealed the induction at O IJ.Mof Piand complete suppression at 250 IJ.M of Pi , these twoconcentrations were treated as P- and P +, respectively forstudying different aspects of Pi deficiency on the expressionof selected genes of maize. For the time course study, rootsfrom both P + and P- treatments were harvested sequentiallyafter 1, 3, 5, 6, 7, 8, 12, and 15 days of growth.Furthermore, after 15 days of growth under P + and P-conditions, roots, stern , young leaves and old leaves wereharvested separately for valuating the spatial expression ofgenes in these tissues.RESULTS AND DISCUSSIONIncreased expression of glycerol-3-phosphate permease77(G3P) was observed under Pi deficiency. G3P is induced inresponse to Pi starvation in maize plants. To adapt to Pistarvation , plant cells have developed a number of altematemetabolic pathways (Plaxton and Carswell, 1999). It islikely that, in addition to the alterations in metabolism,plant cells may have to utilize altemate modes of transport ofphosphorylated compounds. G3P represents a typical sugarP/Pi antiporter possibly localized m chloroplast ormitochondria. The operation of this class of transporter maynot directly impact the Pi concentration in the compartmentin which it functions, as the net Pi change is zero.However, the protein does utilize Pi to move phosphorylatedsugars across the membranes of cellular compartments.Normally Pi levels are tightly controlled in the cell and thiscontrol is likely to be even more stringent under Pi stress.Glycerol-3-phosphate itself is a major precursor in lipidsynthesis as well as a major regulator of metabolism in thecel1. Under Pi starvation the phospho-lipid composition ofmembranes is drastically altered (Essigmann et alo , 1998 jHartel et al., 2000). Phospholipids are replaced bysulpholipids during Pi deficiency. Under these conditions theG3P permease levels may be altered to compensate for thereduced concentrations of phosphorylated sugars. Theexpression of G3P is strongly influenced by altered Pi levelsin the media. A strong induction of the G3P gene wasobserved when the Pi concentration was reduced to 10 fLMinmaize for both efficient and inefficient genotypes. However,the concentration of Pi at which G3P is induced is muchhigher than the naturally occurring Pi concentrations in thesoil (Barber , 1980) . This suggests that phosphatestarvation induced genes are activated well in advance ofimpending biochemical and physiological changes in plants.The induction of G3P is similar to the induction of phosphatetransporters in maize. These results suggest that genesinvolved in phosphate starvation-induced rescue mechanismsare regulated by altered Pi concentration in plants. Adetailed analysis of g!ycerol-3-phosphate permease inArabidopsis and tomato showed that expression of the genedepended on the Pi nutrition status of the plant (Baldwin,2003). The data presented here, taken together with earlierpublished reports, shows that many phosphate starvationinduced responses are repressed and de-repressed bychanging levels of Pi in plant tissues. ln addition,expression of G3P in all parts of the plant is suggestive of itsglobal role in enhancing Pi availability and possible recyclingof organic P compounds. There are many questions that stillneed to be answered regarding cellular and subcellular78localization of G3P. There is a need to evaluate whether G3Pcan transport other phosphorylated sugars in exchange for PioREFERENCESBarber SA. 1980. Soil-plant interactions in the phosphorusnutrition of plants. In , FE Khasawneh, EC Sample, 1 EJKamprath eds , Role of phosphorus in Agriculture ,American Society of Agronomy, Madison, WI, USA: 591-615.Baldwin JC. 2003. Characterization of Phosphate Starvation-lnduced Protein Phosphatase and a Glycerol-3-PhosphatePermease in Arabidopsis and Tomato. Ph. D. , PurdueUniversity. West Lafayette, IN, USA.Eicks M, Maurino V, Knappe S, et alo 2002. The plastidicpentose phosphate translocator represents a link betweenthe cytosolic and the plastidic pentose phosphate pathwaysin plants. Plant Physiol, 128: 512 - 522.Essigmann B, Guler S, Narang RA, et al. 1998. Phosphateavailability affects the thylakoid lipid composition and theexpression of SQD1, a gene required for sulfolipidbiosynthesis in Arabidopsis thaliana. Proc Natl Acad SeiUSA, 95: 1950 - 1955.Griffith JK, Baker ME, Rouch DA, et a!. 1992. Membranetransport proteins , implications of sequence comparisons.Curr Opin Cell Biol, 4: 684 - 695.Hartel H, Dormann P, Benning C. 2000. DGD1-independent biosynthesis of extraplastidic galactolipidsafter phosphate deprivation in Arabidopsis. Proc NatlAcad Sei USA, 97: 10649 -10654.Neuhaus HE , Thom E , Mohlmann T, et a!. 1997.Characterization of a novel ATP/ ADP translocator locatedin the plastid envelope of Arabidopsis thaliana. Plant J,11:73-82.Plaxton WC, Carswell MC. 1999. Metabolic aspects ofphosphate starvation in plants. ln Plant Responses toEnvironmental Stresses , From Phytohormones to GenomeReorganization. Lemer HR ed, Marcel Dekker Inc, NY:349 -372.Streatfield SJ, Weber A, Kinsman EA, et alo 1999. Thephosphoenolpyruvate/ phosphate translocator is requiredfor phenolic metabolism, palisade cell development , andplastid-dependent nuclear gene expression. Plant Cell,11: 1609 - 1622.Weber A, Servaites JC, Geiger DR. et a!. 2000.ldentification, purification, and molecular cloning of aputative plastid glucose translocator. Plant Cell, 12:·787 -802.

Molecular analyses of glycerol-3-phosphate permease-G3P genes induced by phosphate stress in maize.

http://www.alice.cnptia.embrapa.br/alice/bitstream/doc/491123/1/Molecularanalyses.pdf

Molecular analyses of glycerol-3-phosphate permease-G3P genes induced by phosphate stress in maize.

Abstract

Similar works

Full text

Available Versions

Repository Open Access to Scientific Information from Embrapa

Repository Open Access to Scientific Information from Embrapa