Involvement of GPI-anchored lipid transfer proteins in the development of seed coats and pollen inArabidopsis thaliana

Abstract

The non-specific lipid transfer proteins (nsLTPs) constitute a large protein family specific for plants. Proteins from the family are found in all land plants but have not been identified in green algae. Their in vivo functions are still disputed although evidence is accumulating for a role of these proteins in cuticle development. In a previous study, we performed a co-expression analysis of glycosylphosphatidylinositol (GPI)-anchored nsLTPs (LTPGs), which suggested that these proteins are also involved in the accumulation of suberin and sporopollenin. Here, we follow up the previous co-expression study by characterizing the phenotypes of Arabidopsis thaliana lines with insertions in LTPG genes. The observed phenotypes include an inability to limit tetrazolium salt uptake in seeds, development of hair-like structures on seeds, altered pollen morphologies and decreased levels of ω-hydroxy fatty acids in seed coats. The observed phenotypes give further support for a role in suberin and sporopollenin biosynthesis or deposition in A. thaliana.

MYB107 and MYB9 Homologs Regulate Suberin Deposition in Angiosperms

“…With regards to the extracellular transport of suberin, the identification of the putative lipid transporter, LTPG5, being coexpressed with suberin forming tissues, as well as downregulated in myb107, is particularly interesting. In previous work, LTPG1 was shown to be active in the extracellular transport of cuticular lipids in Arabidopsis (Debono et al, 2009), while LTPGs have recently been shown to function in the development of both seed coat and pollen apoplastic barriers (Edstam and Edqvist, 2014). It is therefore likely that LTPG5 is involved in suberin deposition in the seed coat of Arabidopsis in a function mediated through MYB107 activity.…”

“…Genes potentially linked with suberin biosynthesis found to be downregulated in both myb9 and myb107 seeds include those encoding SUS (the putative suberin synthase); an SGNH hydrolase-type esterase superfamily protein (likely involved in lipid metabolic processes; Li-Beisson et al, 2013); CASP-LIKE PROTEIN 1B2 (CASPL1B2, showing strong homology to CASP proteins involved in casparian strip metabolism); LACCASE3 (a member of the laccase family of which LACCASE4 has been demonstrated to be involved in lignin metabolism; Zhao et al, 2013;Schuetz et al, 2014); DIHYDROFLAVONOL 4-REDUCTASE-LIKE1 (DFR-like1; involved in phenylpropanoid metabolism and previously linked to pollen wall development and seed production (Lallemand et al, 2013); and LUPEOL SYNTHASE5 (LUP5; a multifunctional triterpene synthase; Ebizuka et al, 2003). While genes downregulated in myb107 seeds (but not myb9 seeds) encode GPAT5 and ASFT (known to act in suberin formation); 3-KETOACYL-COA SYNTHASE17 (KCS17; a very-long-chain fatty acid synthase); 4-COUMARATE:COA LIGASE5 (4CL5; involved in phenylpropanoid metabolism); and GLYCOSYLPHOSPHATIDYLINOSITOL-ANCHORED LIPID PROTEIN TRANSFER5 (LTPG5; a homolog to the lipid transporter LTPG1; Debono et al, 2009;Edstam and Edqvist, 2014). Finally, the gene encoding CYP86A1, characterized for its involvement in suberin monomer biosynthesis, was downregulated in myb9 seeds (but not myb107 seeds).…”

A lipid transfer protein, OsLTPL36, is essential for seed development and seed quality in rice

“…In general, CFC amounts to 1.6-3.02% of the total weight of brown rice at 14% moisture and plays a major role in rice storage quality [4]. Crude fat content of rice, including palmitic acid (16:0), stearic acid (18:0), oleic acid (18:1), linoleic acid (18:2, 18:3) and several other components, are important factors that determine rice appearance and eating quality [5]. It was reported that alteration of lipid content in rice seed resulted in chalky endosperm.…”

“…NsLTPs facilitate the transportation of fatty acids, phospholipids, and steroids between membranes, which play diverse roles in various biological processes, such as cutin biosynthesis in pollen development, stress response, plant signaling and seed maturation [16,17]. In Arabidopsis thaliana, a GPI-anchored lipid transfer protein was reported to be involved in the development of seed coats and pollen [18]. Two nsLTPs were up-regulated during slow drying treatment in barley and several nsLTPs were identified from dehydration-stressed tissues of cassava [19].…”

Plant lipid transfer proteins: are we finally closing in on the roles of these enigmatic proteins?

“…Anyway, with systematic approaches it will definitely be possible to significantly advance our knowledge in a few years from now. Mosses and liverworts are emerging as models for studies on the assembly, function and evolution of the plant cuticle (31,85,86 …”