Disruption of glycosylphosphatidylinositol‐anchored lipid transfer protein 15 affects seed coat permeability in Arabidopsis

Abstract

The hydrophobic biopolymer suberin, which is deposited in the root endodermis and seed coats, functions as an extracellular barrier against uncontrolled water, gas, and ion loss. Suberin monomers synthesized in the endoplasmic reticulum (ER) are exported through the plasma membrane to the apoplast. However, limited information is available about the molecular mechanisms underlying suberin monomer export and assembly. In this study, we investigated the in planta role of LTPG15 encoding a glycosylphosphatidylinositol (GPI)-anchored lipid transfer protein. LTPG15 was predominantly expressed in the root endodermis and seed coat. Fluorescent signals from LTPG15:eYFP were detected in the plasma membrane in tobacco epidermis. Disruption of LTPG15 caused a significant decrease in the levels of fatty acids (C20-C24), primary alcohols (C20 and C22), x-hydroxy fatty acids (C22 and C24), and a,x-alkanediols (C20 and C22), but an increase in the amounts of primary alcohols and hydroxy fatty acids with C16 and C18 in seed coats. The mutant phenotype was restored to that of the wild type (WT) by the expression of LTPG15 driven by its own promoter. Seed coats of ltpg15 had an increase in permeability to tetrazolium salts compared with WT seed coats. ltpg15 seeds were more sensitive than WT seeds to inhibition of germination and seedling establishment by salt and osmotic stress treatments. Taken together, our results indicate that LTPG15 is involved in suberin monomer export in seed coats, and this highlights the role of Type G non-specific lipid transfer proteins (LTPGs) in very-long-chain fatty acids and their derivatives' export for suberin polyester formation.

Plant Unsaturated Fatty Acids: Multiple Roles in Stress Response

“…Particularly, the half-transporter ABCG11 is shared by them ( Panikashvili et al, 2010 ). Recently, LTPG15, a PM glycosylphosphatidylinositol (GPI)-anchored lipid transfer protein, was identified to participate in suberin monomer export in seed coat ( Lee and Suh, 2018 ). Like transport means, both polymerization mechanism and polymer architecture remain largely elusive.…”

Developmental programs interact with abscisic acid to coordinate root suberization in Arabidopsis

“…Suberin monomers are synthesized enzymatically from precursors derived mainly from fatty acid and phenylpropanoid biosynthesis (Beisson et al ., 2007; Höfer et al ., 2008; Compagnon et al ., 2009; Franke et al ., 2009; Gou et al ., 2009; Lee et al ., 2009; Domergue et al ., 2010). For formation of suberin lamellae, newly synthesized suberin monomers are transported to the apoplast by a number of ATP‐BINDING CASSETTE G transporters as well as GLYCOSYLPHOSPHATIDYLINOSITOL‐ANCHORED LIPID TRANSFER PROTEIN (LTPG15) (Hofmann, 2014; Shiono et al ., 2014; Yadav et al ., 2014; Fedi et al ., 2017; Lee and Suh, 2018). Intriguingly, suberin deposition in the endodermis of Arabidopsis roots has been shown to be highly responsive to various environmental conditions (Barberon et al ., 2016).…”

Molecular basis for neofunctionalization of duplicated E3 ubiquitin ligases underlying adaptation to drought tolerance inArabidopsis thaliana

“…The cell wall category includes eight groups comprised of genes that participate in aspects of cell wall modification and structure. Among these, is glycosylphosphatidylinositol‐anchored lipid transfer protein 15, which is mainly expressed in the root epidermis and seed coat and participates in suberin deposition on cell walls of the root epidermis (Lee and Suh, 2018); eight dirigent‐like genes ( DIR5 – DIR7 , DIR11 – DIR14 and DIR24 ) that may be involved in lignan and lignin biosynthesis as well as in modulating cell wall metabolism in response to stress (Paniagua et al ., 2017); and two expansin genes ( EXPA7 and EXPA18 ) involved in cell wall modification that are expressed during lateral root development and in root hairs, respectively (Lin et al ., 2011a). Others include six HXXXD‐type acyltransferase genes, such as FACT , which is expressed in the endodermis of young roots and may have a function in suberin biosynthesis, and BIA1 and BAT1 , which are highly expressed in roots and involved in brassinosteroid homeostasis (Kosma et al ., 2012; Roh et al ., 2012; Choi et al ., 2013; Zhang and Xu, 2018); five proline‐rich extensin‐like proteins ( EXT7 , EX13 , EX15 , EX21 and EXT22 ), which may participate in cell wall assembly (Saha et al ., 2013); four DUF642 genes ( DGR1 , AT2G41800 , AT5G14150 and AT2G41810 ) that may be involved in the regulation of cell wall events during growth ( DGR1 expression has been detected in the primary root; Cruz‐Valderrama et al ., 2019); and two targeting protein for Xklp2 genes, of which one ( WVD2‐1 ) has been characterized and participates in organ expansion and root waving (Yuen et al ., 2003).…”