Tissue-Specific Expression of a Gene Encoding a Cell Wall-Localized Lipid Transfer Protein from Arabidopsis

Abstract

Nonspecific lipid transfer proteins (LTPs) from plants are characterized by their ability to stimulate phospholipid transfer between membranes in vitro. However, because these proteins are generally located outside of the plasma membrane, it is unlikely that they have a similar role in vivo. As a step toward identifying the function of these proteins, one of severa1 LTP genes from Arabidopsis has been cloned and the expression pattern of the gene has been examined by analysis of the tissue specificity of 8-glucuronidase (CUS) activity in transgenic plants containing LTP promoter-CUS fusions and by in situ mRNA localization. l h e LTPl promoter was active early in development in protoderm cells of embryos, vascular tissues, lignified tips of cotyledons, shoot meristem, and stipules. In adult plants, the gene was expressed in epidermal cells of young leaves and the stem. In flowers, expression was observed in the epidermis of all developing inflorescence and flower organ primordia, the epidermis of the siliques and the outer ovule wall, the stigma, peta1 tips, and floral nectaries of mature flowers, and the petal/sepal abscission zone of mature siliques. l h e presence of CUS activity in guard cells, lateral roots, pollen grains, leaf vascular tissue, and interna1 cells of stipules and nectaries was not confirmed by in situ hybridizations, supporting previous observations that suggest that the reporter gene is subject to artifactual expression. These results are consistent with a role for the LTPl gene product in some aspect of secretion or deposition of lipophilic substances in the cell walls of expanding epidermal cells and certain secretory tissues. l h e LTPl promoter region contained sequences homologous to putative regulatory elements of genes in the phenylpropanoid biosynthetic pathway, suggesting that the expression of the LTPl gene may be regulated by the same or similar mechanisms as genes in the phenylpropanoid pathway.LTPs are small, soluble, basic proteins that are characterized by an ability to catalyze the transfer or exchange of lipids between membranes in vitro (reviewed in Arondel and Kader, 1990). The plant proteins of this class have a broad specificity for the type of lipid they will transfer in vitro, and

Diphtheria Toxin-Mediated Cell Ablation Reveals Interregional Communication during Arabidopsis Seed Development

“…2I). In F 1 seedlings, the GUS pattern did not differ from the reported LTP1::GUS pattern (Thoma et al, 1994; data not shown), and analysis of GFP fluorescence revealed strict epidermal specificity (Fig. 2, J and K).…”

“…The Arabidopsis RPS5A (RIBOSOMAL PROTEIN S5A) promoter is strongly expressed in dividing cells, starting as early as the one-cell embryo stage (Weijers et al, 2001a). The Arabidopsis LTP1 (LIPID TRANSFER PROTEIN 1) promoter marks the L1 layer of all newly formed organs and is preferentially expressed in the apical domain of the embryo (Thoma et al, 1994). The synthetic auxin-responsive DR5(7x) promoter has an expression peak in the central root cap cells of the torpedo stage Arabidopsis embryo (Sabatini et al, 1999).…”

Coordination of apical and basal embryo development revealed by tissue-specific GNOM functions

“…To further analyze the requirement for GNOM in the epidermis, we expressed GNOM from an epidermis-specific promoter in the gnom mutant background. The LIPID-TRANSFER-PROTEIN1 (LTP) promoter is exclusively expressed in the epidermis once the protoderm is formed (Thoma et al, 1994;Baroux et al, 2001). Driving GNOM from this promoter did not result in a discernible rescue phenotype, but introducing the LTP driver construct into the ANT>>GNOM background (LTP+ANT>>GNOM) led to a significant increase in the proportion of rescue phenotypes that showed a complete apical rescue with bilaterally symmetrical spacing of the cotyledons and a corresponding reduction of fusedcotyledon rescue phenotypes (see Table S1B in the supplementary…”

Tissue-Specific Expression and Promoter Analysis of the Tobacco ltp1 Gene

“…The LTPs so far cloned contain a leader sequence responsible for insertion into the ER and subsequent secretion of the protein (Bernhard et al, 1991;Madrid, 1991). In situ hybridizations have shown accumulation of Itp transcripts in epidermal layers of tobacco (Fleming et al, 1992), tomato (Fleming et al, 1993), and Arabidopsis (Thoma et al, 1994), and anti-LTP antibodies recognized epitopes in cell walls and intercellular spaces in Arabidopsis (Thoma et al, 1993). Furthermore, in broccoli, LTP is the most abundant protein in the extracellular wax (Pyee andKolattukudy, 1994, 1995).…”

“…Such a specific localization of LTP in the epidermal cell wall is incompatible with a role in general lipid redistribution, and, in the light of a11 these observations, LTPs have been proposed to play a role in the transport of extracellular lipophilic material. This material could be required for the assembly of cutin (Sterk et al, 1991) and other amorphous barriers around the plant (Koltunow et al, 1990;Sossountzov et al, 1991;Kalla et al, 1994;Thoma et al, 1994).…”