Regulatory Sequences in Apple

Abstract

Apple (Malus × domestica Borkh.) is one of the most important cultivated fruit trees in the world. However, studies on apple gene regulation have long lagged behind model plants due to incomplete information on the genome sequence. This has limited identification and functional characterization of regulatory sequences, that is, numbers, types, and functional roles of genes involved in the regulation of various biological processes in the apple. In general, regulatory sequences can either promote or repress the expression of downstream genes through different regulatory mechanisms, such as protein–DNA binding or protein–protein interactions. Gene expression is highly regulated at the transcriptional level. As a primary type of regulatory sequences, transcription factors (TFs) play critical roles in this process by either positively or negatively regulating the expression of multiple genes, including both downstream structural genes and other regulatory sequences. TFs regulate gene expression by interacting with specific cis-elements in target genes and by forming protein complexes with other TFs to either promote or suppress target gene expression in regulatory modules. Over the past decade, apple whole-genome sequencing efforts have enabled the collection of genomic information on apple TF families and their specific roles in regulation of fruit quality traits, abiotic and biotic stress resistance, and various other important biological traits. In this chapter, we will provide an introduction of apple TFs, and review recent studies on their roles in the regulation of apple growth and development.