The C-terminal propeptide of a plant defensin confers cytoprotective and subcellular targeting functions

Lay, Fung T., Poon, Simon, McKenna, James A., Connelly, Angela A., Barbeta, Barbara L., McGinness, Bruce S., Fox, Jennifer L., Daly, Norelle, Craik, David J., Heath, Robyn L., and Anderson, Marilyn A. (2014) The C-terminal propeptide of a plant defensin confers cytoprotective and subcellular targeting functions. BMC Plant Biology, 14. 41. pp. 1-13.

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Abstract

Background: Plant defensins are small (45–54 amino acids), basic, cysteine-rich proteins that have a major role in innate immunity in plants. Many defensins are potent antifungal molecules and are being evaluated for their potential to create crop plants with sustainable disease resistance. Defensins are produced as precursor molecules which are directed into the secretory pathway and are divided into two classes based on the absence (class I) or presence (class II) of an acidic C-terminal propeptide (CTPP) of about 33 amino acids. The function of this CTPP had not been defined.

Results: By transgenically expressing the class II plant defensin NaD1 with and without its cognate CTPP we have demonstrated that NaD1 is phytotoxic to cotton plants when expressed without its CTPP. Transgenic cotton plants expressing constructs encoding the NaD1 precursor with the CTPP had the same morphology as non-transgenic plants but expression of NaD1 without the CTPP led to plants that were stunted, had crinkled leaves and were less viable. Immunofluorescence microscopy and transient expression of a green fluorescent protein (GFP)-CTPP chimera were used to confirm that the CTPP is sufficient for vacuolar targeting. Finally circular dichroism and NMR spectroscopy were used to show that the CTPP adopts a helical confirmation.

Conclusions: In this report we have described the role of the CTPP on NaD1, a class II defensin from Nicotiana alata flowers. The CTPP of NaD1 is sufficient for vacuolar targeting and plays an important role in detoxification of the defensin as it moves through the plant secretory pathway. This work may have important implications for the use of defensins for disease protection in transgenic crops.

Item ID: 34643
Item Type: Article (Research - C1)
ISSN: 1471-2229
Keywords: plant defensin; phytotoxicity; vacuolar targeting; transgenic cotton
Additional Information:

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Funders: Australian Research Council (ARC), Hexima Limited
Projects and Grants: ARC DP0453107
Date Deposited: 20 Aug 2014 02:29
FoR Codes: 06 BIOLOGICAL SCIENCES > 0607 Plant Biology > 060702 Plant Cell and Molecular Biology @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 100%
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