Phospholipase Dα1-derived phosphatidic acid interacts with ABI1 phosphatase 2C and regulates abscisic acid signaling

Abstract

A bscisic acid (ABA) plays an important role in plant growth, development, and responses to environmental stresses, such as drought, salinity, and low temperature (1). Reversible protein phosphorylation is involved in the early events of ABA signal transduction (2, 3). Specific protein kinases are activated in response to ABA and have been proposed to play a positive role in ABA signaling (2, 4). On the other hand, protein phosphatases 2C (PP2C), such as ABI1, ABI2, and AtPP2CA, are negative regulators in ABA responses (5). The loss of ABI1 or ABI2 PP2C activity in the intragenic revertants of abi1-1 or abi2-1 leads to an enhanced response to ABA (6, 7), whereas overexpression of ABI1 or AtPP2CA blocks the expression of ABAinducible genes in Arabidopsis protoplasts (3). Antisense (AS) inhibition of AtPP2CA results in the enhancement of cold-and ABA-induced gene expression (8). Recently, ABI1 was shown to interact with ATHB6, a transcriptional regulator (9), and with PKS18, a SOS2-like protein kinase (10), whereas ABI2 and AtPP2CA were found to regulate SOS2 kinase and K ϩ channels, respectively (10-12). However, how the activity and function of PP2Cs are regulated in plant cells is still unclear.Recent studies indicate that phospholipase D (PLD) is involved in ABA responses. PLD activity has been implicated in mediating the ABA inhibition of ␣-amylase secretion (13), ABA-regulated stomatal movement (14), and ABA-induced gene expression (15,16). Arabidopsis has 12 PLDs, and multiple types of PLDs display distinctly different catalytic and regulatory properties (17). Molecular and genetic data have indicated that a specific PLD participates in signaling the ABA response. AS inhibition of PLD␣1 diminished stomatal closure induced by ABA or drought and increased water loss in Arabidopsis, whereas overexpression of PLD␣1 resulted in an increased sensitivity to ABA (18). In addition, specific PLDs have been shown to regulate many other plant functions, including cell patterning, programmed cell death, and stress tolerance (19-21). However, the direct target of PLD action is unknown. In this study, we present evidence for a direct link between PLD␣1 and PP2C in the ABA signaling response. Materials and Methods Plant Materials and Growth.A T-DNA-insertional mutant of PLD␣1 (PLD␣1-KO) was identified from SALK 053785 seeds obtained from the Arabidopsis Biological Resource Center (Columbus, OH). The site of T-DNA insertion was confirmed by DNA sequencing. The generation of PLD␣1-AS plants was described in ref. 22. Seeds of PLD␣1-KO, PLD␣1-AS, and wild type of Arabidopsis thaliana (ecotype Columbia) were sown in soil and kept at 4°C for 2 days. Plants were grown in a growth chamber with cool white fluorescent light of 100 mol m Ϫ2 ⅐s Ϫ1 under 14-h light͞10-h dark and 23°C͞18°C cycles.Water Loss and Stomatal Aperture Measurements. Detached leaves from 6-week-old plants were exposed to cool white light (125 mol m Ϫ2 ⅐s Ϫ1 ) at 23°C. Leaves were weighed at various time intervals, and the loss of fresh weight (%) was used to in...

Phosphatidic Acid Binds to Cytosolic Glyceraldehyde-3-phosphate Dehydrogenase and Promotes Its Cleavage in Arabidopsis

“…In addition to regulating the catalytic activity, PA may tether its binding proteins to membranes. PA tethers ABI1 to the plasma membrane, resulting in prevention of ABI1 from translocation into the nucleus where it binds to ATHB6, a transcription factor that negatively regulates ABA responses (18,25). A similar process was observed in yeast that PA bound and prevented a transcriptional repressor Opi1 from entering the nucleus where it suppresses lipid biosynthesis (26,27).…”

“…These observations could mean that reduced, active GAPC is involved in the glycolysis for cellular energy production whereas its oxidized, inactive form may be utilized for cell signaling through its interaction with other cellular compounds. PLD␦, together with PLD␣1, is known to be involved in ABA signaling (18,23,29). The PA produced by oxidized GAPC-enhanced PLD␦ activity may associate with GAPC in a feedback loop to modulate the PLD␦ activity, possibly by degrading GAPC as described below, to desensitize the ABA signaling machinery (29).…”

Overexpression of the Arabidopsis 10-Kilodalton Acyl-Coenzyme A-Binding Protein ACBP6 Enhances Freezing Tolerance

“…many species of PC, PE, and PG, but increases in their metabolites, PA, and lysophospholipids (Welti et al, 2002). Two phospholipases that produce PA from phospholipids and that mediate freezing tolerance are PLDd, which plays a positive role, and PLDa1, which plays a negative role (Welti et al, 2002;Zhang et al, 2004;Rajashekar et al, 2006;Li et al, 2008). During freezing treatment, the PLDa1 mutant displayed enhanced freezing tolerance, with decreases in freezing-induced hydrolysis of PC, and therefore generated less PA Rajashekar et al, 2006;Li et al, 2008).…”

Double Knockouts of Phospholipases Dζ1 and Dζ2 in Arabidopsis Affect Root Elongation during Phosphate-Limited Growth But Do Not Affect Root Hair Patterning

“…PLD previously has been proposed to play a pivotal role in many cellular processes, including signal transduction, membrane trafficking, cytoskeletal rearrangements, and membrane degradation (Wang, 2002). PLDa1 and PLDd were demonstrated to function in freezing and drought tolerance (Sang et al, 2001;Welti et al, 2002;Li et al, 2004;Zhang et al, 2004). PLDz1 and PLDz2 are distinctively different from other PLDs; they have phox homology (PX) and pleckstrin homology (PH) domains that are also found in mammalian PLDs (Qin and Wang, 2002).…”