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Antifungal plant defensins MtDef4 and MtDef5: Mechanisms of action and engineering transgenic peanut resistant to Aspergillusflavus and aflatoxin accumulation

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Relation http://oar.icrisat.org/10820/
 
Title Antifungal plant defensins MtDef4 and MtDef5: Mechanisms of action and engineering transgenic peanut resistant to Aspergillusflavus and aflatoxin accumulation
 
Creator Shah, D
Kaur, J
Islam, T
Velivelli, S
Sharma, K K
Bhatnagar-Mathur, P
 
Subject Biotechnology
Crop Improvement
Food Processing & Technology
Groundnut
Genetics and Genomics
Food Security
Aflatoxins
 
Description Fungal pathogens impose major constraints on crop yields globally. Host defense peptides have evolved
in plants to protect from the damaging effects of fungal pathogens. Defensins are sequence divergent
cysteine-rich antifungal peptides of innate immunity expressed in all plants. They exhibit potent antifungal
activity in vitro and therefore have potential for use in transgenic crops for enhanced resistance
to fungal pathogens. MtDef4 and MtDef5 are two sequence-divergent apoplast-localized defensins expressed
in Medicago truncatula. MtDef4 is a monomeric defensin of 47 amino acids, whereas MtDef5
is a novel bi-domain defensin containing two monomeric domains linked by a 7-amino acid peptide.
These defensins differ from each other in sequence, net charge and hydrophobicity. MtDef4 inhibits the
growth of several filamentous fungi including Fusarium graminearum at micromolar concentrations.
In contrast, the bi-domain MtDef5 inhibits the growth of these fungi at submicromolar concentrations.
Two ascomycete fungi N. crassa and F. graminearum respond differently to MtDef4 challenge1
. Membrane
permeabilization is required for the antifungal activity of MtDef4 against F. graminearum but not
against N. crassa. MtDef4 is internalized by these fungi, but is targeted to different subcellular compartments
in each fungus. In contrast, MtDef5 rapidly permeabilizes the plasma membrane of both fungi
and induces accumulation of reactive oxygen species. It is also internalized by these fungi, but uses
spatially distinct modes of entry into these fungi. It co-localizes with cellular membranes, travels to
nucleus and becomes dispersed in other subcellular locations2
. MtDef4 binds to plasma membrane resident
bioactive phospholipid phosphatidic acid (PA), whereas MtDef5 binds to several phospholipids
but with strong preference for phosphatidylinositol monophosphates, PI3P, PI4P and PI5P. MtDef5
forms oligomers in presence of PIP, PI and PA1,2. Thus, MtDef4 and MtDef5 exhibit different modes
of antifungal action and have strong potential for use as unique antifungal agents in transgenic crops.
Aflatoxins, secondary metabolites produced by Aspergillus flavus, are extremely toxic carcinogenic
compounds. Aflatoxin contamination caused by A. flavus infection of peanuts poses a major threat to
public health in developing countries of sub-Saharan Africa and Asia. Transgenic peanut lines overexpressing
apoplast-targeted MtDef4 have been generated. When challenged with A. flavus, peanut
seeds expressing this defensin exhibit strong resistance to this pathogen and accumulate extremely low
levels of aflatoxins3
. This is the first study to demonstrate highly effective biotechnological strategy for
successfully generating transgenic peanuts that are near-immune to aflatoxin contamination, offering a
panacea for food safety for people in developing countries.
 
Date 2018
 
Type Conference or Workshop Item
PeerReviewed
 
Format application/pdf
 
Language en
 
Rights —
 
Identifier http://oar.icrisat.org/10820/1/Antifungal%20plant%20defensins%20MtDef4%20and%20MtDef5.pdf
Shah, D and Kaur, J and Islam, T and Velivelli, S and Sharma, K K and Bhatnagar-Mathur, P (2018) Antifungal plant defensins MtDef4 and MtDef5: Mechanisms of action and engineering transgenic peanut resistant to Aspergillusflavus and aflatoxin accumulation. In: 16th Naples Workshop on Bioactive Peptides, Naples, Italy, June 7-9, 2018.