RAGHOTHAMA, K. G.

VASCONCELOS, M. J.

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Expression of Bat-3 and phosphate stress induced genes in maize and sorghumVasconcelos, M.J.'; Raghothama K. G. 2'Embrapa Maize and Sorghum, PO box151, Sete Lagoas, MG, Brazil, 35701-9702 Department ofHorticulture and Landscape Architecture, Purdue University, WestLafayette- IN 47907IntroductionPhosphate unavailability is a growth-limiting factor for plants in many natural ecosystems.To thrive under Pi limited conditions plants have developed efficient mechanisms of phosphateacquisition and utilization of absorbed phosphorus in plant tissue. ln order to decipher moleculardeterminants which could have a potential role in phosphorus acquisition and utilization efficiency,further studies on expression profiles of some ofthe phosphate responsive genes identified throughmicroarray analysis were done. The advent ofDNA microarray technology has made possible theanalysis of global pattems of gene expression and revealed unexpected networks of coordinatedregulation (Lockhart et al., 1996). The evaluation of expression ofthousands of genes by microarrayanalyses in parallel has become an important tool in functional genomics. Recently, Girke et al.(2000) have identified genes which are transcriptionally regulated by different concentrations ofphosphate. ln collaboration with Pioneer HiBred Co. we have conducted a microarray analysis of asubset of genes expressed in maize. The microarray chips used were referred to as "metabolicchips" and "transcription factor chips". Analysis was done with RNA isolated from P+ and P- rootsand cobs. A set of genes were selected for expression analysis and further characterization. Basedon the results of RNA blot experiments, Bat-3 gene was selected for further maize and sorghum .analyses described in thisstudy.MethodologyEight Zea mays and seven Sorghum bico/ar lines developed and identified by Embrapa,maize and sorghum were used in these studies. The lines were categorized as phosphorus efficientor inefficient based on the comparative grain production when grown in dark red oxisols with lowand high phosphorus levels (2mg/kg and 15mg/kg, respectively). Seeds of each genotype weregerminated in trays containing Scott's ready earth plug mix (Scotts Co., Marysville, OH) and grownin the greenhouse for one week. One-week-old seedlings were removed from the soil medium. Theroots were washed and the plants were transferred to a hydroponics set-up containing half-strengthmodified Hoagland's solution (Liu et al., 1998). One week after transferring the seedlings tohydroponics the experimental treatments were initiated. Sets of plants were transferred to half strengthnutrient solution with Pi (250 IlM) or without Pi (O IlM). The solutions were changed every twodays to maintain the concentration of nutrients and pH. Furthermore, after 15 days of growth underP+ and P- conditions, roots, stem, young leaves and old leaves were harvested separately forevaluating the spatial expression of genes in these tissues. Maize and sorghum plants grown inhydroponic culture were used to study the expression of Bat-3 gene under Pi starvation conditions.Results and DiscussionDistinct changes in the expression of phosphate starvation induced genes in maize andsorghum genotypes were observed. lnterestingly Bat-3 is strongly suppressed under phosphatedeficiency. These genes exhibit temporal, spatial and phosphate deficiency associated pattems ofexpression. Although there were differences in the expression of phosphate starvation inducedgenes, no consistent pattem of expression associated with either phosphate efficient or inefficientgenotypes of maize or sorghum emerged. It appears that phosphate efficiency in tropical maize andsorghum is a complex trait mediated by coordinated action of groups of genes either induced or144 Proceedings of 3ni International Symposium on Phosphorus Dynamics in the Soil-Plant Continuumsuppressed in response to nutrient deficiency. The majority ofthe gene expression studies during Pideficiency are primarily focused on genes that are induced in response to Pi starvation. One interestingoutcome of this study is the identification of a Bat-3 homolog, expression of which is stronglysuppressed during Pi deficiency. There is no assigned function for this gene in plants although thereare indieations that it may be regulated similar to heat shock proteins (HSPs) in animal systems(Baneji et al., 1990). To the best of our knowledge this is the first gene that is described to be downregulated during phosphorus starvation. Although the functional significance ofthis down regulationis not clear at present, this may serve as an indication of ehanges in Pi homeostasis during phosphorusdefieiency or ressuply to plants. The suppression ofthis gene is not similar in all genotypes, especiallyfor maize, where some genotypes had only a slight decrease in the transcript level whereas in othersthe expression was almost completly suppressed. In addition, sorghum genotypes showed consistentdown regulation of this gene during Pi deficieney. Similar to other genes Bat-3 expression wasinfluenced by altered Pi levels in the media. The gene expression was completely restored whenboth efficient and inefficient genotypes were supplied with 100 j.tMofPi. More studies are requiredto understand the regulation and function ofthis gene under phosphorus stress condition. Isolationand eharacterization of Bat-3 gene from plants may help in this endeavor.ReferencesBaneji J, Sands J, Strominger JL, Spies T (1990) Proc Natl Acad Sei USA 87: 2374-2378Girke T, Todd J, Ruuska S, White J, Benning e, Ohlrogge J (2000). Plant Physiol 124: 1570-1581Liu e, Muchhal US, Mukatira U, Kononowiez AK and Raghothama KG (1998). Plant Physiol116:91-95Loekhart DJ, Dong H, Byme Me, Follettie MT, Gallo MV, ehee MS, Mittmann M, Wang e,Kobayashi M, Horton H, Brown, EL (1996). Nature Biotechnol. 14: 1675-1680.Proceedings 013"/ International Symposium on Phosphorus Dynamics in the Soil-Plant Continuum 145

Expression of Bat-3 and phosphate stress induced genes in maize and sorghum.

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