Targeting and localization of wound-inducible leucine aminopeptidase A in tomato leaves.

Abstract

The constitutive and wound-inducible leucine aminopeptidases (LAP-N and LAP-A, respectively) of tomato encode 60-kDa proteins with 5-kDa presequences that resemble chloroplast-targeting peptides. Cell fractionation studies and immunoblot analyses of chloroplast and total proteins have suggested a dual location of the mature LAP-A proteins in the cytosol and the plastids. In this study, the subcellular localization of tomato LAPs was further investigated using in vitro chloroplast-targeting assays and immunocytochemical techniques at the light and TEM levels. In vitro-translated LAP-A1 and LAP-N preproteins were readily transported into pea chloroplasts and processed into mature proteins of 55 kDa indicating the presence of a functional chloroplast-targeting signal in the LAP-A1 and LAP-N protein precursors. In addition, a LAP polyclonal and a LAP-A-specific antisera were used to immunolocalize LAP proteins in leaves from healthy, wounded and methyl jasmonate (MeJA)-treated plants. Low levels of LAPs and/or LAP-like proteins were detected in leaves from unwounded plants. The LAP polyclonal antiserum, which detected LAP-A, LAP-N and LAP-like proteins, and the LAP-A specific antibodies, which detected only LAP-A, showed that LAP levels increased in leaf sections after wounding and MeJA treatments. LAP-A proteins were primarily detected within the chloroplasts of spongy and palisade mesophyll cells. The localization of LAP-A was distinct from the location of early wound-response proteins that are important in the biosynthesis of jasmonic acid or systemin and more similar to the late wound-response proteins with primary roles in defense. The importance of these findings relative to the potential roles of LAP-A in defense is discussed.

• Authors: Javier Narváez-Vásquez, Chao-Jung Tu, Sang-Youl Park, Linda L Walling
• Journal: Planta (Planta) Vol. 227 Issue 2 Pg. 341-51 (Jan 2008) ISSN: 0032-0935 [Print] Germany
• PMID: 17896114 (Publication Type: Journal Article, Research Support, U.S. Gov't, Non-P.H.S.)

Chemical References

• Leucyl Aminopeptidase

Topics

• Amino Acid Sequence
• Gene Expression Regulation, Plant
• Immunohistochemistry
• Leucyl Aminopeptidase (metabolism)
• Solanum lycopersicum (enzymology)
• Plant Leaves (enzymology)
• Protein Transport