The mechanism of the transcription factor ZjWRKY55 in regulating resistance to black spot rot in jujube fruit

Abstract

Ziziphus jujuba, with its thin and crispy skin, sweet taste, and high economic and nutritional value, is a popular fresh fruit. Black spot rot, instigated by Alternaria alternata (A. alternata), stands as a primary post-harvest affliction impacting jujube. Compared to traditional fungicides, amino acid treatment as a biological control method is safer and environmentally friendly, without any harm to humans or the environment. Previous studies have shown that treating jujube fruit with methionine (Met) can enhance the enzymatic activity of lignin synthesis-related enzymes and increase the expression of transcription factors (TFs) such as ZjWRKY55, thereby improving the resistance of jujube fruit. This study mainly focuses on investigating the mechanism of how the transcription factor ZjWRKY55 regulates the resistance of jujube fruit. Transient overexpression of ZjWRKY55 in jujube significantly reduces the lesion diameter and incidence rate of black spot rot and significantly increases the lignin content in jujube fruit. RNA sequencing (RNA-seq) analysis of the transiently transformed samples reveals significant enrichment of differentially expressed genes involved in pathways such as sugar metabolism, amino acid metabolism, phenylpropane biosynthesis, and alpha-linolenic acid metabolism. Real-time fluorescence quantitative PCR (RT-qPCR) indicates upregulated expression of genes such as ZjCCoAOMT, ZjGAD, ZjCAD, ZjPER, and ZjBGLU. Dual-luciferase reporter (DLR) assays and electrophoretic mobility shift (EMSA) assays demonstrate that ZjWRKY55 can directly bind to the upstream promoters of ZjCCoAOMT and ZjGAD to activate their transcriptional expression and bind to the promoter of ZjKTI5 to downregulate its expression.