Enhanced phosphorus nutrition in monocots and dicots over-expressing a phosphorus-responsive type I H+-pyrophosphatase.

Plants challenged by limited phosphorus undergo dramatic morphological and architectural changes in their root systems in order to increase their absorptive surface area. In this paper, it is shown that phosphorus deficiency results in increased expression of the type I H+-pyrophosphatase AVP1 (AVP, Arabidopsis vacuolar pyrophosphatase), subsequent increased P-type adenosine triphosphatase (P-ATPase)-mediated rhizosphere acidification and root proliferation. Molecular genetic manipulation of AVP1 expression in Arabidopsis, tomato and rice results in plants that outperform controls when challenged with limited phosphorus. However, AVP1 over-expression and the resulting rhizosphere acidification do not result in increased sensitivity to AlPO4, apparently because of the enhancement of potassium uptake and the release of organic acids. Thus, the over-expression of type I H+-pyrophosphatases appears to be a generally applicable technology to help alleviate agricultural losses in low-phosphorus tropical/subtropical soils and to reduce phosphorus runoff pollution of aquatic and marine environments resulting from fertilizer application.

Plant proton pumps.

Chemiosmotic circuits of plant cells are driven by proton (H(+)) gradients that mediate secondary active transport of compounds across plasma and endosomal membranes. Furthermore, regulation of endosomal acidification is critical for endocytic and secretory pathways. For plants to react to their constantly changing environments and at the same time maintain optimal metabolic conditions, the expression, activity and interplay of the pumps generating these H(+) gradients have to be tightly regulated. In this review, we will highlight results on the regulation, localization and physiological roles of these H(+)- pumps, namely the plasma membrane H(+)-ATPase, the vacuolar H(+)-ATPase and the vacuolar H(+)-PPase.

Yeast hygromycin sensitivity as a functional assay of cyclic nucleotide gated cation channels.

Cyclic nucleotide gated cation channels (CNGCs) are a large (20 genes in Arabidopsis thaliana) family of plant ligand gated (i.e. cyclic nucleotides activate currents) ion channels, however, little is known about their functional properties. One reason for this is the recalcitrance of plant CNGC expression in heterologous systems amenable to patch clamp studies. Here, we show results demonstrating the efficacy of using growth of a K+ uptake-deficient yeast (trk1,2) as a functional assay of CNGCs as inwardly-conducting cell membrane cation (K+) transporters. Prior work demonstrated that trk1,2 is hypersensitive to the antibiotic hygromycin (hyg) and that expression of an inwardly conducting K+ transporter suppresses hyg hypersensitivity. We find that increasing [hyg] in solid YPD medium inhibits trk1,2 growth around a filter disk saturated with 3 M K+. Northern analysis indicated that message is transcribed in trk1,2 transformed with the CNGC coding sequences. Confocal imaging of yeast expressing CNGC-fluorescent fusion proteins indicated channel targeting to the cell membrane. Trk1,2 expressing several plant CNGCs grown in the presence of hyg demonstrated (a) greater growth than trk1,2 transformed with empty plasmid, and (b) enhanced growth when cAMP was added to the medium. Alternatively, cAMP inhibited growth of yeast transformed with either the empty plasmid, or the plant K+ channel KAT1; this channel is not a CNGC. Growth of trk1,2 was dependent on filter disk [K+]; suggesting that complementation of hyg hypersensitivity due to presence of a functional plant CNGC was dependent on K+ movement into the cytosol. We conclude that plant CNGC functional characterization can be facilitated by this assay system.