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Phosphatidylinositol 3-kinases (PI3Ks) are characterized by the presence of a C2 domain at the N-terminal end (class I, III); or at both the N-terminal and C-terminal ends (class II), sometimes including a Plextrin homology domain and/or a Ras domain. Plant PI3Ks are analogous to the class III mammalian PI3K. An N-terminal fragment (~170 aa) of the tomato PI3K regulatory domain including the C2 domain, was cloned and expressed in a bacterial system. This protein was purified to homogeneity and its physicochemical properties analyzed. The purified protein showed strong binding with monophosphorylated phosphatidylinositols, and the binding was dependent on calcium ion concentration and pH. In the overall tertiary structure of PI3K, C2 domain showed unique characteristics, having three antiparallel beta-sheets, hydrophobic regions, acidic as well as alkaline motifs, that can enable its membrane binding upon activation. To elucidate the functional significance of C2 domain, transgenic tobacco plants expressing the C2 domain of PI3K were generated. Transgenic plants showed defective pollen development and disrupted seed set. Flowers from the PI3K–C2 transgenic plants showed delayed wilting, and a decrease in ethylene production. It is likely that introduction of the PI3K–C2 segment may have interfered with the normal binding of PI3K to the membrane, delaying the onset of membrane lipid catabolism that lead to senescence. Image 1 • Tomato PI3K–C2 fragment was cloned, purified and biochemically characterized. • Transgenic tobacco plants expressing the C2-GFP domain were generated. • Flowers from the transgenic plants showed delayed flower senescence. • Over-expression of C2 may have interfered with the normal binding of PI3K to the membrane, delaying senescence. [ABSTRACT FROM AUTHOR]

Abstract: Sunflower (Helianthus annuus L.) is a commercially important oilseed crop. Previous studies proved that this crop is a promising plant species for phytoextraction of excess soil phosphorus (P) because of its superior P accumulating characteristics. Suppression subtractive hybridization (SSH) strategy was employed to isolate and characterize genes that are induced in response to high P in this crop. SSH library was prepared using cDNA generated from plants treated with high P as the ‘tester’. Based on the results of dot blot analysis, 360 positive cDNA clones were selected from the SSH library for sequencing. A total of 89 non-redundant expressed sequence tags (ESTs) were identified as high P-responsive genes and they were classified into 6 functional groups. Several genes involved in metabolism showed markedly preferential expression in the library. For further confirmation, thirteen of the representative ESTs were selected from all categories for RT-PCR analysis and the results showed up-regulation of these genes in response to high P-treatment. The gene expression data derived from this study suggested that several of the up-regulated genes identified under high P-treatment might be involved in P-accumulation and tolerance in this plant. [Copyright &y& Elsevier]

Abstract: Recurrent application of animal manure to the soil often results in accumulation of phosphorus (P) in the soil over time. Use of temperate forages like Lolium multiflorum capable of extracting excess P from manure impacted soil is an attractive strategy for P phytoremediation. Two genotypes of L. multiflorum, ‘Gulf and Marshall’ were grown in soil and hydroponic media containing various concentrations of poultry manure and their P accumulation potential was determined. A decline in the biomass with an increase in manure concentration beyond 10gkg−1 soil in Gulf and 25gkg−1 soil in Marshall was noticed. Gulf grass accumulated more P content (7gkg−1 dry weight) as compared to Marshall (6gkg−1 dry weight) in both roots and shoots. Maximum shoot P content was observed in the soil amended with 10g poultry manure, while root P was highest at the concentration of 50g poultry manurekg−1 in the soil. Both cultivars yielded the highest biomass when grown in the presence of 10g poultry manure in modified Hoagland''s media. Presence of chelators in the media did not produce any noticeable effect on P accumulation in either grass and the biomass was appreciably enhanced by all concentrations of the chelators. Gulf and Marshall ryegrass seedlings were grown hydroponically in various poultry manure fractions. Both phytase and acid phosphatase (APase) enzyme activities in the root increased substantially in response to P-sufficient condition. In the presence of various poultry manure fractions, an intermediate level of both enzymes was measured compared to the P-sufficient condition, while the lowest enzyme activity was observed in the absence of any P source in the media. The level of APase and phytase activities was more or less the same in the two grasses under various growth conditions. An additional APase isoform was induced specifically in response to P-starvation from the two grass cultivars. Phytase and APase assays carried out in the P-starved and P-replenished grass seedlings further confirmed that during P deficiency, the enzyme activity was lowest and results of PAGE indicated that an APase isoform was induced under P-starvation. [Copyright &y& Elsevier]