Identification of a new polyphosphoinositide in plants, phosphatidylinositol 5-monophosphate (PtdIns5P), and its accumulation upon osmotic stress

Abstract

Polyphosphoinositides play an important role in membrane trafficking and cell signalling. In plants, two PtdInsP isomers have been described, PtdIns3P and PtdIns4P. Here we report the identification of a third, PtdIns5P. Evidence is based on the conversion of the endogenous PtdInsP pool into PtdIns(4,5)P(2) by a specific PtdIns5P 4-OH kinase, and on in vivo (32)P-labelling studies coupled to HPLC head-group analysis. In Chlamydomonas, 3-8% of the PtdInsP pool was PtdIns5P, 10-15% was PtdIns3P and the rest was PtdIns4P. In seedlings of Vicia faba and suspension-cultured tomato cells, the level of PtdIns5P was about 18%, indicating that PtdIns5P is a general plant lipid that represents a significant proportion of the PtdInsP pool. Activating phospholipase C (PLC) signalling in Chlamydomonas cells with mastoparan increased the turnover of PtdIns(4,5)P(2) at the cost of PtdIns4P, but did not affect the level of PtdIns5P. This indicates that PtdIns(4,5)P(2) is synthesized from PtdIns4P rather than from PtdIns5P during PLC signalling. However, when cells were subjected to hyperosmotic stress, PtdIns5P levels rapidly increased, suggesting a role in osmotic-stress signalling. The potential pathways of PtdIns5P formation are discussed.

A phosphatidylinositol phosphate-specific myo-inositol polyphosphate 5-phosphatase required for seedling growth

“…The decrease in PtdIns(3)P is consistent with the ability of 5PTase11 to hydrolyze PtdIns(3,5)P 2 in vitro (Ercetin and Gillaspy 2004). It should be noted, however, that we and others have not been able to detect PtdIns(3,5)P 2 in Arabidopsis, so its presence remains elusive in higher plants, in contrast to its established role in algae (Meijer et al 1999;Meijer et al 2001).…”

The Highly Charged Region of Plant β-type Phosphatidylinositol 4-kinase is Involved in Membrane Targeting and Phospholipid Binding

“…Genetic and physiological studies revealed the involvement of PI pathway in many developmental processes in bacterial or mammalian cells, including transcriptional regulation (Ginsburg and Kimmel, 1989;Guo et al, 2001), cytoskeleton rearrangement (Takenawa and Itoh, 2001), membrane trafficking (Rameh and Cantley, 1999;Driscoll, 2001;Gaidarov et al, 2001;Takenawa and Itoh, 2001), and endocytosis (Yang et al, 1996;Yue et al, 2001). In higher plants, PI and its derivatives have also been demonstrated to be critical in regulating gene transcription (Bunney et al, 2000), membrane biogenesis and vesicle trafficking (Roth, 1999;Kim et al, 2001), cytoskeleton dynamics (Staiger et al, 1997;Hinchliffe et al, 1998) and responses to external stimuli (DeWald et al, 2001;Meijer et al, 2001;Takahashi et al, 2001;Zien et al, 2001;Jung et al, 2002;Ruelland et al, 2002;Park et al, 2003). To date, several plant cDNAs encoding key enzymes of the plant PI signaling pathway have been isolated, including those for PI synthase (Xue et al, 2000), PI 3-kinase (Hong and Verma, 1994;Welters et al, 1994), PI4K (Okpodu et al, 1995;Stevenson et al, 1998;Xue et al, 1999), PIPK (Mikami et al, 1998), PI-PLC (Hirayama et al, 1995;Shi et al, 1995), inositol polyphosphate phosphatase (Berdy et al, 2001), and others.…”

Involvement of phospholipase C in the responses triggered by extracellular phosphatidylinositol 4-phosphate

“…These PPIs can play different roles as signalling molecules in diverse biological processes, such as vesicle trafficking, or as substrates for the production of other second messengers (Meijer and Munnik, 2003). In plant and animal systems, PI4P has been found to be the most abundant PPI, making up approximately 80-90% of the monophosphorylated isoforms (Munnik et al, 1994;Rameh et al, 1997;Meijer et al, 2001). PI4P has been mainly characterized as the precursor of PI(4,5)P 2 , implicated in the phospholipase C (PLC)-mediated signalling.…”