LIPID–HORMONE CROSSTALK MEDIATED BY WRKY125 AND LOX4 ENHANCES RESISTANCE TO FUSARIUM VERTICILLIOIDES IN MAIZE

Fusarium verticillioides (Fv) is a major cereal pathogen causing stalk rot and ear rot in maize, negatively affecting crop productivity, and compromising food safety by producing the secondary metabolites fumonisins. Several studies were conducted to identify maize genes associated with host plant resistance to Fv infection and fumonisin accumulation. The maize WRKY transcription factors and the lipoxygenases (LOXs) are well recognized as important players in plant defense against pathogens, and it is known that the host-pathogen lipid crosstalk influences the pathogenesis. In this regard, previous RNA-seq experiments reported the enhanced expression of LOX genes in maize resistant genotypes and GWAS resulted in one SNP significantly associated with WRKY125. The Clustered Regularly Interspaced Short Palindromic Repeat/associated Cas9 (CRISPR/Cas9) editing of WRKY125 and the transgenic overexpression of LOX4 genes were carried out to investigate the possible implication of these two genes in the resistance mechanisms against Fv. Wrky125 edited lines showed a decrease by about 5 and 4 times of Fusarium ear rot severity and fumonisin contamination, respectively, compared to the wild-type genotype. RNA-seq analysis highlighted an enhanced modulation of the jasmonic acid (JA) and abscisic acid (ABA) hormones, redox state, cell wall modification, and secondary metabolism-associated genes after fungal infection in the mutant background in contrast to wildtype. Moreover, the increased expression of JA- and ABA-related genes correlated with a wider accumulation of these two phytohormones. LOX4 overexpression also resulted in enhanced resistance to Fv infection and fumonisin contamination. Transcriptomic and lipidomic analyses revealed that LOX4 mutants up-regulated expression of 9-LOX and JA-related genes, thereby increasing the production of 9-oxylipins and JA-related metabolites under fungal infection. Further studies will be conducted to explore the effects of WRKY125-editing and LOX4- overexpression on other fungi and abiotic stresses.