Abstract
The cotton fibers are seed trichomes that elongate from the ovule epidermis. Polar lipids are required for the quick enlargement of cell membrane and fiber cell growth, however, how lipids are transported from the ovules into the developing fibers remains less known. Here, we reported the functional characterization of GhLTPG1, a GPI-anchored lipid transport protein, during cotton fiber elongation. GhLTPG1 was abundantly expressed in elongating cotton fibers and outer integument of the ovules, and GhLTPG1 protein was located on cell membrane. Biochemical analysis showed that GhLTPG1 specifically bound to phosphatidylinositol mono-phosphates (PtdIns3P, PtdIns4P and PtdIns5P) in vitro and transported PtdInsPs from the synthesis places to the plasma membranes in vivo. Expression of GhLTPG1 in Arabidopsis caused an increased number of trichomes, and fibers in GhLTPG1-knockdown cotton plants exhibited significantly reduced length, decreased polar lipid content, and repression of fiber elongation-related genes expression. These results suggested that GhLTPG1 protein regulates the cotton fiber elongation through mediating the transport of phosphatidylinositol monophosphates.
Highlights
Promote the sphingolipid biosynthesis by up-regulating serine palmitoyltransferase[10] and supplement of VLCFAs in the ovule culture medium significantly enhances the elongation rate of fiber cells
Phosphatidylinositols serve as the constituents of fiber cell membrane and important signaling molecules during cotton fiber elongation[6,11]
The notable increase of phosphatidylinositol monophosphates (PIs) in cotton fiber occurs at the early stage of fiber elongation[6,30], reflecting a large requirements for the assembly of expanding cell membranes and the membrane maintenance in quick developing fibers
Summary
Promote the sphingolipid biosynthesis by up-regulating serine palmitoyltransferase[10] and supplement of VLCFAs in the ovule culture medium significantly enhances the elongation rate of fiber cells. Previous studies suggested that lipid transfer proteins (LTPs) are likely the candidates delivering the phospholipids to developing cells[6,14,15] considering that most LTPs are abundantly expressed in the epidermis of developing tissues[16,17,18,19]. LTPs contain a hydrophobic pocket capable of binding long chain fatty acids[17,20], and studies showed that plant LTPs are involved in transporting lipids from the endoplasmic reticulum (ER) to plasma membrane (PM) and subsequently from PM to the cell exterior[21,22,23]. Many studies have focused on the functional identification of genes/proteins involving in activation and repression of cotton fiber elongation[11,29,30,31], the mechanisms underlying phospholipid transportation and their effects have been scarcely investigated. Suppressed GhLTPG1 resulted in the shorter fibers, which was attributable to the decreased lipids content in elongating fibers
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