Characterization of the ZmUXT2 and ZmLRR-RLK Candidate Tar Spot Resistance Genes in Maize

Abstract

Tar spot is an emerging fungal disease that threatens maize production across North America due to a lack of genetic resistance in cultivated varieties. A major quantitative trait locus (qRtsc8-1) is associated with tar spot resistance in maize and putatively contains four candidate genes. We found that two of these genes, ZmUXT2 and ZmLRR-RLK, are induced by microbe-associated molecular patterns (MAMPs). ZmUXT2 is a predicted UDP-xylose transporter and has higher expression in a tar spot resistant genotype compared to a susceptible genotype. ZmLRR-RLK has similar expression between tar spot resistant and susceptible genotypes. The resistant maize genotype had higher MAMP-induced ROS accumulation and gene expression relative to the susceptible maize genotype. The coding sequences of ZmUXT2 and ZmLRR-RLK genes were similar between resistant and susceptible maize genotypes with between 1-16 amino acid changes. Fluorescently tagged ZmUXT2 localized to the endoplasmic reticulum, while ZmLRR-RLK localized to both the endoplasmic reticulum and plasma membrane during transient expression in Nicotiana benthamiana. No differences in subcellular localization were observed between resistant and susceptible alleles. Together, this suggests that inducible immunity influences expression of ZmUXT2 and ZmLRR-RLK genes and that a tar spot resistant maize genotypes supports higher expression of ZmUXT2 compared to a susceptible genotype even in the absence of stress.