Characterization of Glycosylphosphatidylinositol-Anchored Lipid Transfer Protein 2 (LTPG2) and Overlapping Function between LTPG/LTPG1 and LTPG2 in Cuticular Wax Export or Accumulation in Arabidopsis thaliana

Abstract

Cuticular waxes are synthesized by the extensive export of intracellular lipids from epidermal cells. However, it is still not known how hydrophobic cuticular lipids are exported to the plant surface through the hydrophilic cell wall. The LTPG2 gene was isolated based on Arabidopsis microarray analysis; this gene is predominantly expressed in stem epidermal peels as compared with in stems. The expression of LTPG2 transcripts was observed in various organs, including stem epidermis and silique walls. The composition of the cuticular wax was significantly altered in the stems and siliques of the ltpg2 mutant and ltpg1 ltpg2 double mutant. In particular, the reduced level of the C29 alkane, which is the major component of cuticular waxes in ltpg1 ltpg2 stems and siliques, was similar to the sum of reduced values of either parent. The total cuticular wax load was reduced by approximately 13% and 20% in both ltpg2 and ltpg1 ltpg2 siliques, respectively, and by approximately 14% in ltpg1 ltpg2 stems when compared with the wild-type. Similarly, severe alterations in the cuticular layer structure of epidermal cells of ltpg2 and ltpg1 ltpg2 stems and silique walls were observed. In tobacco epidermal cells, intracellular trafficking of the fluorescent LTPG/LTPG1 and LTPG2 to the plasma membrane was prevented by a dominant-negative mutant form of ADP-ribosylation factor 1, ARF1(T31N). Taken together, these results indicate that LTPG2 is functionally overlapped with LTPG/LTPG1 during cuticular wax export or accumulation and LTPG/LTPG1 and LTPG2 are targeted to the plasma membrane via the vesicular trafficking system.

Plant lipid transfer proteins: Evolution, expression and function

“…This would be a suitable role for the nsLTPs, and knockout mutants of a couple of LTPGs have altered lipid composition in the cuticle (DeBono et al, 2009;Lee et al, 2009;Kim et al, 2012). This theory is strengthen by our investigation showing that nsLTPs are found in all land plants, together with evidence of a protective lipid layer present in the moss Physcomitrella.…”

“…This has indirectly been shown for some Type G nsLTPs in Arabidopsis, where knockout/knockdown mutants have a lower wax load in the stem compared to wild-type plants (Debono et al, 2009;Lee et al, 2009;Kim et al, 2012). Their exact role in this lipid deposition, or the mechanism behind it, is however not clarified.…”

The Nonspecific Lipid Transfer Protein AtLtpI-4 Is Involved in Suberin Formation of Arabidopsis thaliana Crown Galls

“…In Arabidopsis, the ABCG transporter ABCG11 has been associated with both cutin and suberin biosynthesis (Bird et al, 2007;Panikashvili et al, 2007Panikashvili et al, , 2010, while CER5/ABCG12 (Pighin et al, 2004) and ABCG13 (Panikashvili et al, 2011) are required for the export of cuticular wax monomers (Panikashvili and Aharoni, 2008;McFarlane et al, 2010). For cuticular wax assembly, also nonspecific lipid transfer proteins (nsLTPs) likely facilitate the transfer of aliphatic compounds (Lee et al, 2009;Kim et al, 2012). The Arabidopsis LTPG1 has been associated with cuticular wax biosynthesis (DeBono et al, 2009).…”

The Formation and Function of Plant Cuticles

“…Export of some wax compounds also appears to be facilitated by glycosylphosphatidylinositol (GPI)-anchored lipid-transfer proteins (LTPs), LTPG1 and LTPG2, which are bound to the extracellular side of the plasma membrane (Debono et al, 2009;Lee et al, 2009;Kim et al, 2012). These proteins represent a unique class of LTPs, a family of small and typically soluble proteins that bind a variety of lipid substrates in vitro (Yeats and Rose, 2008).…”