The Expression and Sequence Analysis of MdMATE52 in Apple Roots During Activation of Defense Against Pythium ultimum Infection

To understand the molecular regulation of host defense responses in the pathosystem between apple roots and a necrotrophic oomycete pathogen Pythium ultimum, a series of transcriptome analyses have revealed a multi-phase and multi-layer defense tactic in apple root tissues. Among the most notable transcriptome changes during defense activation in apple roots, upregulation of genes involved in phenylpropanoid biosynthesis, transport of secondary metabolites, and lignin formation appeared to be the key defense themes which may crucially impact the outcome of plant–pathogen interactions. From our transcriptome datasets, the MdMATE52 gene, which encodes a MATE transporter, was shown to be differentially expressed between a resistant and a susceptible apple rootstock genotype in response to P. ultimum infection. The cis elements at promoter regions and sequence variations within coding regions of MdMATE52 were compared among several resistant and susceptible apple rootstock genotypes as well as various Malus species. The stronger upregulated expression patterns of MdMATE52 appeared to be correlated with the observed resistance traits among various genotypes. Our results suggested that minimal but clearly identifiable sequence variations may contribute to the genotype-specific expression and function of MdMATE52. The findings from this study should facilitate future experiments such as site-specific mutation and Crispr-based genome editing to define the regulation mechanisms of MdMATE52 and function during defense activation in apple roots.