Guo, L, Mishra, G, Markham, JE, Li, M, Tawfall, A, Welti, R et al.. Connections between sphingosine kinase and phospholipase D in the abscisic acid signaling pathway in Arabidopsis. J Biol Chem 287: 8286-8296
Phosphatidic acid (PA) and phytosphingosine 1-phosphate (phyto-S1P) both are lipid messengers involved in plant response to abscisic acid (ABA). Our previous data indicate that PA binds to sphingosine kinase (SPHK) and increases its phyto-S1P-producing activity. To understand the cellular and physiological functions of the PA-SPHK interaction, we isolated Arabidopsis thaliana SPHK mutants sphk1-1 and sphk2-1 and characterized them, together with phospholipase Dα1 knock-out, pldα1, in plant response to ABA. Compared with wild-type (WT) plants, the SPHK mutants and pldα1 all displayed decreased sensitivity to ABA-promoted stomatal closure. Phyto-S1P promoted stomatal closure in sphk1-1 and sphk2-1, but not in pldα1, whereas PA promoted stomatal closure in sphk1-1, sphk2-1, and pldα1. The ABA activation of PLDα1 in leaves and protoplasts was attenuated in the SPHK mutants, and the ABA activation of SPHK was reduced in pldα1. In response to ABA, the accumulation of long-chain base phosphates was decreased in pldα1, whereas PA production was decreased in SPHK mutants, compared with WT. Collectively, these results indicate that SPHK and PLDα1 act together in ABA response and that SPHK and phyto-S1P act upstream of PLDα1 and PA in mediating the ABA response. PA is involved in the activation of SPHK, and activation of PLDα1 requires SPHK activity. The data suggest that SPHK/phyto-S1P and PLDα1A are co-dependent in amplification of response to ABA, mediating stomatal closure in Arabidopsis.
"Strikingly PLDα1 is also a target for LCB-P that stimulate PtdOH synthesis (Guo and Wang, 2012). This apparent simplicity turns to complexity when considering that (i) PtdOH generated by PLDα1 interacts with and further stimulates the LCB kinase SPHK1 (Guo et al., 2012) and (ii) that a ABA-triggered NO production is also required for the activation of Phospholipase Dδ and PtdOH synthesis (Distéfano et al., 2012). In this intricate signaling network, further investigations should now examine the consequences of alterations of NO or SL signaling on each other to clearly establish possible direct NO–SL crosstalks. "
[Show abstract][Hide abstract] ABSTRACT: Nitric oxide (NO) emerged as one of the major signaling molecules operating during plant development and plant responses to its environment. Beyond the identification of the direct molecular targets of NO, a series of studies considered its interplay with other actors of signal transduction and the integration of NO into complex signaling networks. Beside the close relationships between NO and calcium or phosphatidic acid signaling pathways that are now well-established, recent reports paved the way for interplays between NO and sphingolipids (SLs). This mini-review summarizes our current knowledge of the influence NO and SLs might exert on each other in plant physiology. Based on comparisons with examples from the animal field, it further indicates that, although SL-NO interplays are common features in signaling networks of eukaryotic cells, the underlying mechanisms and molecular targets significantly differ.
"The interplay between PLD and SPHK pathways could be complex. PA is involved in the activation of SPHK, but activation of PLDa1 requires SPHK activity, suggesting that SPHK and PLDa1 are co-dependent in amplification of the ABA response-mediating stomatal closure in Arabidopsis (Guo et al. 2012). "
[Show abstract][Hide abstract] ABSTRACT: Phosphoglycerolipids are essential structural constituents of membranes and some also have important cell signalling roles. In this review, we focus on phosphoglycerolipids that are mediators in hormone signal transduction in plants. We first describe the structures of the main signalling phosphoglycerolipids and the metabolic pathways that generate them, namely the phospholipase and lipid kinase pathways. In silico analysis of Arabidopsis transcriptome data provides evidence that the genes encoding the enzymes of these pathways are transcriptionally regulated in responses to hormones, suggesting some link with hormone signal transduction. The involvement of phosphoglycerolipid signalling in the early responses to abscisic acid, salicylic acid and auxins is then detailed. One of the most important signalling lipids in plants is phosphatidic acid. It can activate or inactivate protein kinases and/or protein phosphatases involved in hormone signalling. It can also activate NADPH oxidase leading to the production of reactive oxygen species. We will interrogate the mechanisms that allow the activation/deactivation of the lipid pathways, in particular the roles of G proteins and calcium. Mediating lipids thus appear as master players of cell signalling, modulating, if not controlling, major transducing steps of hormone signals.
"Secondly, work from the Wang laboratory showed that phyto-S1P does not activate PLDα1 directly in vitro (Guo et al., 2012). S1P and phyto-S1P were found to stimulate an intracellular calcium increase (Ng et al., 2001; Kim et al., 2007), and calcium is a key factor required for PLDα1 activity (see this review by Guo and Wang). "
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