Spatial and temporal expression of a maize lipid transfer protein gene.

Abstract

We studied the temporal and spatial pattern of lipid transfer protein (LTP) gene expression, as well as the localization of this protein, in maize. Using an LTP gene, we observed an accumulation of LTP mRNA in embryos and endosperms during seed maturation. LTP gene expression was also investigated in young seedlings. After germination, the leve1 of LTP mRNA in the coleoptile increased, with a maximum at 7 days, whereas LTP mRNA levels were low in the scutellum and negligible in roots. The high levels of LTP mRNA found in coleoptiles and embryos were confirmed by in situ hybridization. Moreover, LTP gene expression appeared to be localized in the externa1 cellular layers and around the leaf veins. Using immunogold methods, we also observed that LTP was distributed heterogeneously in the different cells of coleoptiles and leaves. The highest concentrations of LTP were found in the outer epidermis of the coleoptiles as well as in the leaf veins. Together, our observations indicate that LTP gene expression is not only organ specific and time specific but also cell specific.

Isolation of a root-specific cDNA encoding a ns-LTP-like protein from the roots of bean (Phaseolus vulgaris L.) seedlings

“…Plant nsLTPs share 43~o to 64~o amino acid sequence homology with each other and have the following common characteristics: (1) the presence of eight cysteine residues at conserved locations; (2) a signal peptide; (3) a molecular mass of ca. 9 kDa; and (4) a basic isoelectric point of approximately 9 [2,17]. These characteristics are also applicable to the PVR3 protein, except that PVR3 protein shows a pI of 6.8.…”

“…[2,7,14,17,18,23]. On the basis of this result, it was suggested that a ns-LTP isoform might be expressed specifically in root tissue [1,2,17]. The expression pattern of PVR3 cDNA, which is rootspecific (Fig.…”

“…However, immunohistochemical evidence has made it clear that these proteins are extracellular and, therefore, cannot fulfill that proposed role [17,22,23]. It has been suggested that these proteins may play a role in a number of different biological functions through their abilities to bind and carry lipophilic compounds such as cutin monomers or cuticular components [2,17,18,23]. It has been shown in vitro that plant ns-LTPs are potent growth inhibitors of bacterial and fungal pathogens [13,20].…”

“…strates between membranes and they are widely distributed in eukaryotic and prokaryotic cells [2,20]. All of the plant ns-LTP genes reported previously have been expressed preferentially in the aerial parts of plants, although active lipid transport takes place in the root [1,2,17]. In this paper, we describe the root-specific accumulation of PVR3 m R N A encoding a ns-LTP like protein and discuss a model of the three-dimensional structure predicted from the deduced sequence of the PVR3 protein.…”

The biochemistry and molecular biology of plant lipid biosynthesis

“…Originally it was believed that lipid-binding proteins were possibly involved in lipid transfer between organelles. Three recent observations would strongly question this conclusion: (1) maize lipid transfer protein has been immunolocalized and found predominantly in the external cellular layers and around the leaf veins [128]; (2)the EP2 lipid transfer protein in embryogenic carrot suspensions is secreted into the medium [131]; (3)the Arabidopsis lipid transfer protein has an extracellular location [138]. It is possible that lipid transfer proteins are involved in wax or cutin synthesis.…”