Inositol Phospholipid Metabolism in Arabidopsis. Characterized and Putative Isoforms of Inositol Phospholipid Kinase and Phosphoinositide-Specific Phospholipase C

Abstract

Phosphoinositides (PIs) constitute a minor fraction of total cellular lipids in all eukaryotic cells. They fulfill many important functions through interaction with a wide range of cellular proteins. Members of distinct inositol lipid kinase families catalyze the synthesis of these phospholipids from phosphatidylinositol. The hydrolysis of PIs involves phosphatases and isoforms of PI-specific phospholipase C. Although our knowledge of the roles played by plant PIs is clearly limited at present, there is no doubt that they are involved in many physiological processes during plant growth and development. In this review, we concentrate on inositol lipid-metabolizing enzymes from the model plant Arabidopsis for which biochemical characterization data are available, namely the inositol lipid kinases and PI-specific phospholipase Cs. The biochemical properties and structure of characterized and genome-predicted isoforms are presented and compared with those of the animal enzymes to show that the plant enzymes have some features clearly unique to this kingdom.Phosphatidylinositol (PtdIns) is a major phospholipid in eukaryotic cells. Three of the five free hydroxyl groups of PtdIns can be phosphorylated in cells in different combinations. In total, seven phosphorylated derivatives of PtdIns have been detected, one of which, PtdIns 3,4,5-trisphosphate [PtdIns(3,4,5)P 3 ], has not been found in plant cells (Fig. 1). These inositol phospholipids are collectively referred to as phosphoinositides (PIs). In animal cells, PIs and their derivatives operate in signal transduction pathways triggered by stimuli as diverse as growth factors, hormones, neurotransmitters, and light (Berridge, 1993).Historically, the first major insight into the importance of PIs was the discovery that the two PtdIns 4,5-bisphosphate [PtdIns(4,5)P 2 ]-derived second messengers inositol 1,4,5-trisphosphate [Ins(1,4,5)P 3 ] and diacylglycerol promote Ca 2ϩ release from internal stores and activate protein kinase C, respectively (Berridge and Irvine, 1989; for review, see Berridge, 1993). The production of these two second messengers from PtdIns(4,5)P 2 is catalyzed by PI-specific phospholipase C (PI-PLC) isoforms. During the last decade, it has become evident that in addition to serving as precursors to Ins(1,4,5)P 3 and diacylglycerol, PIs actively participate in several other cellular processes. They have been shown to regulate the dynamics of the actin cytoskeleton through interaction with actin-binding proteins (Lassing and Lundberg, 1985; Janmey and Stossel, 1987; Brill et al., 2000), and to potentiate the activation of protein kinase C (Oh et al., 1998), PI-PLC (Bae et al., 1998; Falasca et al., 1998), and phospholipase D (Pappan et al., 1997). In addition, PIs phosphorylated at the D3-hydroxy group of the inositol head group are required for specific vesicle trafficking steps (De Camilli et al., 1996; Wurmser et al., 1999) and are able to activate the protein kinase Akt/PKB and PI-dependent kinases (Wymann and Pirola, 1998). A 3-phosphoryla...

The role of phospholipase D in plant stress responses

“…the PX-PH PLDs, plants possess an additional subfamily, namely the C2 PLDs. Interestingly, the opposite seems to be true for the phosphoinositide-specific phospholipase C (PLC) family, which consists of five classes in animals and is restricted to one class in plants (Cockcroft, 2006;Mueller-Roeber and Pical 2002). Moreover, phosphatidic acid (PA) seems to play a central role in plant PLD and PLC signaling, whereas diacylglycerol (DAG) appears to be the prominent second messenger in animal PLD and PLC signaling events.…”

MORN motifs in plant PIPKs are involved in the regulation of subcellular localization and phospholipid binding

“…Of the other three putative OsPIPKs, two of them, OsPIPK2 and OsPIPK8, are truncated peptides that lacked the N-terminus and the other, OsPIPK6, lacks the corresponding EST sequence in the database. In another model plant, Arabidopsis, there are 11 genes encoding PIPK proteins, which are highly similar to AtPIP5K1 [33], and only two proteins lack the MORN motifs. However, whether these two putative AtPIPKs are expressed is at present unclear, as no mRNA or EST sequences have been reported for either of them [33].…”

“…In another model plant, Arabidopsis, there are 11 genes encoding PIPK proteins, which are highly similar to AtPIP5K1 [33], and only two proteins lack the MORN motifs. However, whether these two putative AtPIPKs are expressed is at present unclear, as no mRNA or EST sequences have been reported for either of them [33]. Structural organization Figure 3A).…”

Global Expression Profiling Applied to the Analysis of Arabidopsis Stamen Development

“…Two major types (termed II and III) of PtdIns 4-kinases have been identified in animals and plants. At2g40850 encodes a type II PtdIns 4-kinase, which has been previously named PI4Kg1 (Mueller-Roeber and Pical, 2002). While the function of type II PtdIns 4-kinases in plants is unknown, it has been suggested that in animals, they are involved in the regulation of intracellular trafficking (Wang et al, 2003;Salazar et al, 2005).…”