Seung Ho Chung,Mahdiyeh Bigham,Ryan R. Lappe,Barry Chan,Ugrappa Nagalakshmi,Steven A. Whitham,Savithramma P. Dinesh-Kumar,Georg Jander

Plant Biotechnology Journal; September 2021; Volume 19(9): 1713-1724

Summary

Spodoptera frugiperda (fall armyworm) is a notorious pest that threatens maize production worldwide. Current control measures involve the use of chemical insecticides and transgenic maize expressing Bacillus thuringiensis (Bt) toxins. Although additional transgenes have confirmed insecticidal activity, limited research has been conducted in maize, at least partially due to the technical difficulty of maize transformation. Here, we describe implementation of a sugarcane mosaic virus (SCMV) vector for rapidly testing the efficacy of both endogenous maize genes and heterologous genes from other organisms for the control of S. frugiperda in maize. Four categories of proteins were tested using the SCMV vector: (i) maize defence signalling proteins: peptide elicitors (Pep1 and Pep3) and jasmonate acid conjugating enzymes (JAR1a and JAR1b); (ii) maize defensive proteins: the previously identified ribosome-inactivating protein (RIP2) and maize proteinase inhibitor (MPI), and two proteins with predicted but unconfirmed anti-insect activities, an antimicrobial peptide (AMP) and a lectin (JAC1); (iii) lectins from other plant species: Allium cepa agglutinin (ACA) and Galanthus nivalis agglutinin (GNA); and (iv) scorpion and spider toxins: peptides from Urodacus yaschenkoi (UyCT3 and UyCT5) and Hadronyche versuta (Hvt). In most cases, S. frugiperda larval growth was reduced by transient SCMV-mediated overexpression of genes encoding these proteins. Additionally, experiments with a subset of the SCMV-expressed genes showed effectiveness against two aphid species, Rhopalosiphum maidis (corn leaf aphid) and Myzus persicae (green peach aphid). Together, these results demonstrate that SCMV vectors are a rapid screening method for testing the efficacy and insecticidal activity of candidate genes in maize.

See https://onlinelibrary.wiley.com/doi/10.1111/pbi.13585

Figure 2: Use of a sugarcane mosaic virus (SCMV) to transiently express GFP in maize. (a) Schematic diagram of the SCMV-CS3 cloning vector. A multiple cloning site (MCS) was inserted between P1 and HC-Pro genes of SCMV. 35S: cauliflower mosaic virus 35S promoter; T: NOS terminator. (b) Mosaic infection symptoms of SCMV vector in maize three weeks post-inoculation. (c) Transient overexpression of GFP in plants infected by SCMV-empty vector (EV) or -GFP. Gene expression was determined by qRT-PCR three weeks post-inoculation. Means ± SE of N = 5, ***P < 0.001, t-test. (d) Confocal image of foliar GFP expression. (e,f) S. frugiperda survival and larval growth on plants infected by EV or SCMV-GFP. Two-day-old caterpillars were fed on infected plants for one week and caterpillar mass was determined. Means ± SE of N = 10, EV, empty vector; NS, non-significant; MCS, multiple cloning site