Phospholipase A2 Is Required for PIN-FORMED Protein Trafficking to the Plasma Membrane in theArabidopsisRoot  

Abstract

Phospholipase A 2 (PLA 2 ), which hydrolyzes a fatty acyl chain of membrane phospholipids, has been implicated in several biological processes in plants. However, its role in intracellular trafficking in plants has yet to be studied. Here, using pharmacological and genetic approaches, the root hair bioassay system, and PIN-FORMED (PIN) auxin efflux transporters as molecular markers, we demonstrate that plant PLA 2 s are required for PIN protein trafficking to the plasma membrane (PM) in the Arabidopsis thaliana root. PLA 2 a, a PLA 2 isoform, colocalized with the Golgi marker. Impairments of PLA 2 function by PLA 2 a mutation, PLA 2 -RNA interference (RNAi), or PLA 2 inhibitor treatments significantly disrupted the PM localization of PINs, causing internal PIN compartments to form. Conversely, supplementation with lysophosphatidylethanolamine (the PLA 2 hydrolytic product) restored the PM localization of PINs in the pla 2 a mutant and the ONO-RS-082-treated seedling. Suppression of PLA 2 activity by the inhibitor promoted accumulation of trans-Golgi network vesicles. Root hair-specific PIN overexpression (PINox) lines grew very short root hairs, most likely due to reduced auxin levels in root hair cells, but PLA 2 inhibitor treatments, PLA 2 a mutation, or PLA 2 -RNAi restored the root hair growth of PINox lines by disrupting the PM localization of PINs, thus reducing auxin efflux. These results suggest that PLA 2 , likely acting in Golgi-related compartments, modulates the trafficking of PIN proteins.

A Small Phospholipase A2-α from Castor Catalyzes the Removal of Hydroxy Fatty Acids from Phosphatidylcholine in Transgenic Arabidopsis Seeds

“…2). In relation to subcellular localization, both Arabidopsis homologs AtsPLA 2 a and AtsPLA 2 b and the rice homolog OssPLA 2 a possess signal sequences as predicted by PSORT (http://psort.hgc.jp) and have been localized previously to the endoplasmic reticulum (ER) or Golgi (Seo et al, 2008;Matos and Pham-Thi, 2009;Lee et al, 2010;Singh et al, 2012). A common motif (-LHKP) is found at the C terminus of both the rice and castor sPLA 2 a sequences, constituting a putative ER retention signal (Singh et al, 2012).…”

“…Evidence for the involvement of sPLA 2 in signaling and pathogen defense is more limited (Munnik and Testerink, 2009;Canonne et al, 2011). Their involvement in membrane trafficking, however, is emerging: reductions in sPLA 2 expression in Arabidopsis (Arabidopsis thaliana) plants led to Golgi disruption and the inhibition of PIN auxin efflux transporter traffic to the plasma membrane in roots (Lee et al, 2010) and also to membrane disruption in pollen (Kim et al, 2011). Two other proteins, SOBER1 (Kirik and Mudgett, 2009) and Lecithin Cholesterol Acyltransferase (LCAT)-like4 , unrelated to these three main families, also have been identified as PLA 2 s.…”

“…They are involved in several biological processes in both animals and plants (Chen et al, 2011): (1) as a component of the acylation/ hydrolysis of phospholipids in the so-called Lands cycle involved in primary lipid metabolism in animals (Lands, 1960;Balsinde and Dennis, 1997;Imae et al, 2010) and plants (Li et al, 2013); (2) in membrane architecture and trafficking (Lee et al, 2010;Kim et al, 2011); (3) in the production of bioactive compounds involved in signaling, pathogen defense, and programmed cell death (Munnik and Testerink, 2009;Canonne et al, 2011); (4) in catalyzing the hydrolysis of oxidized lipids (van Kuijk et al, 1987;Banas et al, 1992); (5) in seed storage lipid mobilization (Rudolph et al, 2011);and (6) in uncommon and modified FA production in seeds (Bafor et al, 1991;Ståhl et al, 1995;Bates and Browse, 2011).…”

The salt stress-induced LPA response in Chlamydomonas is produced via PLA2 hydrolysis of DGK-generated phosphatidic acid

“…In plants, however, these receptors are missing, and in a unicellular alga, it is not very likely that LPA is secreted and sensed by others. Nonetheless, other functions for PLA 2 products have been described, and during the last few years, several advances in plant PLA 2 signaling in higher plants have been made (37)(38)(39)(40).…”

“…In Arabidopsis , a novel PLA 2 , SOBER1 , with no homology to any of the plant PLA families, was suggested to suppress the elicitor-induced induction of a hypersensitive response by reducing the accumulation of PA ( 43 ). However, based on in vitro activity of recombinant SOBER1, its substrate was speculated to be PC rather than PA. Other recent plant studies implicating a role for PLA 2 includes auxin signaling ( 39 ), pH regulation ( 44,45 ), plant defense ( 37,(43)(44)(45)(46), stomatal opening ( 47 ), pollen development and germination ( 48 ), and vesicular transport ( 39,48 ). For PA, putative protein targets have been identifi ed in a proteomics screen using PA-affi nity beads ( 49 ).…”