Do phosphoinositides regulate membrane water permeability of tobacco protoplasts by enhancing the aquaporin pathway?

Enhancing the membrane content of PtdInsP 2 , the already-recognized protein-regulating lipid, increased the osmotic water permeability of tobacco protoplasts, apparently by increasing the abundance of active aquaporins in their membranes. While phosphoinositides are implicated in cell volume changes and are known to regulate some ion channels, their modulation of aquaporins activity has not yet been reported for any organism. To examine this, we compared the osmotic water permeability (P f) of protoplasts isolated from tobacco (Nicotiana tabacum) cultured cells (NT1) with different (genetically lowered or elevated relative to controls) levels of inositol trisphosphate (InsP3) and phosphatidyl inositol [4,5] bisphosphate (PtdInsP2).

Increasing Phosphatidylinositol (4,5)-Bisphosphate Biosynthesis Affects Basal Signaling and Chloroplast Metabolism in Arabidopsis thaliana.

One challenge in studying the second messenger inositol(1,4,5)-trisphosphate (InsP₃) is that it is present in very low amounts and increases only transiently in response to stimuli. To identify events downstream of InsP₃, we generated transgenic plants constitutively expressing the high specific activity, human phosphatidylinositol 4-phosphate 5-kinase Iα (HsPIPKIα). PIP5K is the enzyme that synthesizes phosphatidylinositol (4,5)-bisphosphate (PtdIns(4,5)P₂); this reaction is flux limiting in InsP₃ biosynthesis in plants.

Phosphatidylinositol 4,5-bisphosphate influences PIN polarization by controlling clathrin-mediated membrane trafficking in Arabidopsis.

The functions of the minor phospholipid phosphatidylinositol-4,5-bisphosphate [PtdIns(4,5)P2] during vegetative plant growth remain obscure. Here, we targeted two related phosphatidylinositol 4-phosphate 5-kinases (PI4P 5-kinases) PIP5K1 and PIP5K2, which are expressed ubiquitously in Arabidopsis thaliana. A pip5k1 pip5k2 double mutant with reduced PtdIns(4,5)P2 levels showed dwarf stature and phenotypes suggesting defects in auxin distribution.

Phosphatidylinositol 4-kinase and phosphatidylinositol 4-phosphate 5-kinase assays.

Inositol lipid kinases are perhaps the easiest and most straightforward enzymes in the phosphoinositide pathway to analyze. In addition to monitoring lipid kinase-specific activity, lipid kinase assays can be used to quantify the inositol lipids present in isolated membranes (Jones et al., Methods Mol Biol 462:75-88, 2009).

Enhanced Agrobacterium-mediated transformation efficiencies in monocot cells is associated with attenuated defense responses.

Plant defense responses can lead to altered metabolism and even cell death at the sites of Agrobacterium infection, and thus lower transformation frequencies. In this report, we demonstrate that the utilization of culture conditions associated with an attenuation of defense responses in monocot plant cells led to highly improved Agrobacterium-mediated transformation efficiencies in perennial ryegrass (Lolium perenne L.).