Identification of Phosphate (Pi)-Regulated Genes in Sunflower by Suppression Subtractive Hybridization.

Phosphate (Pi) is one of the essential macronutrient that plays an important role in many physiological and biochemical processes in plants. To increase soil fertility, application of enormous quantities of phosphorus-rich manures to the soil often exceeding plant P- requirements has become routine in many parts of the US. This excess P run-off from agricultural lands leads to eutrophication and other serious water quality issues. Mining of excess soil P with the help of plants capable of extracting P from soil without external P application has been proposed as an attractive strategy for remediation of P-contaminated soils. With a view to identify possible P- hyperaccumulators, several plants were screened in P-enriched soils. Sunflower (Helianthus annus) displayed high biomass growth as well as P accumulation in their aboveground biomass. We generated suppression subtractive cDNA library to understand the Pi-regulated gene expression in this plant. For this, RNA was isolated from shoot and roots of plants grown under P-sufficient and P-deficient hydroponic conditions and used for library synthesis. All the positive clones from the library were differentially screened by dot blot hybridization. Differentially expressed clones were then selected for sequencing. A number of Pi-responsive cDNAs were identified which include inorganic phosphate transporter, polyubiquitin, phenylalanine ammonia lyase, beta 1, 3-glucanase, translation elongation factor 1a, carbohydrate oxidase.