One major advance in modern biochemistry and cell biology in recent years has been the realization that phospholipids are rich sources for generating mediators and are active participants in cell regulation. Activation of phospholipases (PL) is often an early event in the cascade of signal transduction. Phospholipase D (PLD) (EC constitutes a major phospholipase family in plants that hydrolyzes phospholipids to produce phosphatidic acid (PA) and a free head group, such as choline, ethanolamine, or serine. This activity is widespread and readily detectable

College of Life Science, State Key Laboratory of Crop Genetics and Germplasm Enhancement, Nanjing Agricultural University, Nanijing 210095, P R, China e-mail: [email protected] X. Wang (*)

Department of Biology, University of Missouri, St. Louis and Donald Danforth Plant Science Center, St. Louis, MO 63121, USA e-mail: [email protected]

T. Munnik (ed.), Lipid Signaling in Plants, Plant Cell Monographs 16,

DOI 10.1007/978-3-642-03873-0_3, © Springer-Verlag Berlin Heidelberg 2010

in various plant tissues. PLD was first discovered in plants, about 60 years ago. Early studies have provided valuable information on the biochemical properties and occurrence of the enzyme. For example, the discovery that PLD can transfer the phosphatidyl moiety to a primary alcohol has been useful in current studies concerning the activity of PLD and PA functions in cells.

The application of molecular approaches, albeit later than other families of phospholipases, has propelled the PLD research to a new era. The first cloning of PLD from castor bean was a catalyst for cloning PLDs from different sources, including yeast and mammals (Wang et al. 1994). This was followed by identification and analysis of multiple PLDs, revealing biochemical, molecular, and functional heterogeneity of the PLD family. Over the past 10 years, considerable progress has been made toward understanding the function of PLDs in processes of plant growth, development, and stress response (Bargmann and Munnik 2006; Wang et al. 2006). In particular, the role of PLD in producing PA as a class of lipid messengers has received increasing attention. Recent results have led to the proposition that "PA (is) promoted to manager" in mammalian cells (Hancock 2007). The notion of PA as cellular manager is applicable to the regulation of not only G proteins (Zhao et al. 2007), but also protein phosphorylation, transcription, and translation in glycerolipid biosynthesis, cell proliferation, and growth. PLD and PA are involved in a wide variety of plant processes, ranging from responses to hormones, drought, salinity, cold, freezing, nutrient deficiencies, and pathogens, to root growth, senescence, reproduction, and seed quality. They affect these processes through roles in cell signaling, membrane trafficking, and cytoskeletal rearrangement, as well as lipid remodeling and membrane degradation. The exciting developments in PLD research have been the subject of several recent reviews (Wang 2000, 2005, 2002; Testerink and Munnik 2005; Zhang et al. 2005; Bargmann and Munnik 2006; Wang et al. 2006). The signaling function of PA has also been reviewed recently (Testerink and Munnik 2005; Wang et al. 2006), which revealed that PA is not only generated via PLD but also via diacylglycerol kinase (see also chapters "Diacylglycerol Kinase," "Phosphatidic Acid - An Electrostatic/ Hydrogen- Bond Switch?," "Nitric Oxide and Phosphatidic Acid Signaling in Plants"). Here, the recent progress in PLD research in plants is outlined.

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