Abstract
Knotted1-like Homeobox (KNOX) proteins play important roles in regulating plant growth, development, and other biological processes. However, little information is available on the KNOX gene family in apple (Malus domestica Borkh.). In this study, 22 KNOX genes were identified in the apple genome. The gene structure, protein characteristics, and promoter region were characterized. The MdKNOX family members were divided into three classes based on their phylogenetic relationships. Quantitative real-time PCR analysis revealed that the majority of MdKNOX genes exhibited strongly preferential expression in buds and were significantly up-regulated during the flower induction period. The transcript levels of MdKNOX genes were responsive to treatments with flowering- and stress-related hormones. The putative upstream regulation factor MdGRF could directly bind to the promoter of MdKNOX15 and MdKNOX19, and inhibit their transcriptional activities, which were confirmed by yeast one-hybrid and dual-luciferase assays. The results provide an important foundation for future analysis of the regulation and functions of the MdKNOX gene family.
Highlights
Homeobox proteins are considered to act as sequence-specific DNA-binding proteins and contain a 60 amino-acid-long DNA-binding domain termed a homeodomain (HD) that directly regulates the expression of specific groups of target genes (Hayashi and Scott, 1990)
Four Class I (SHOOT-MERISTEMLESS (STM), KNAT1, KNAT2, and KNAT6) and Four Class II KNOTTED1-LIKE HOMEOBOX (KNOX) (KNAT3, KNAT4, KNAT5, and KNAT7) genes were identified from Arabidopsis
The 22 MdKNOX genes were located on 12 chromosomes in the apple genome
Summary
Homeobox proteins are considered to act as sequence-specific DNA-binding proteins and contain a 60 amino-acid-long DNA-binding domain termed a homeodomain (HD) that directly regulates the expression of specific groups of target genes (Hayashi and Scott, 1990). Different HD proteins have been grouped into separate families (or classes) based on either sequence identity within the HD or conserved protein motifs outside of the HD (Bürglin and Affolter, 2016). Despite several reports of expression patterns, comparatively little is known about the function of Class II KNOX genes in plants. Promoter-GUS and fluorescent protein analysis have demonstrated the transcriptional regulation and protein products localization of KNAT3, KNAT4, and KNAT5 in specific domains and cell types of the Arabidopsis root (Truernit et al, 2006). Three Class II KNOX genes, MtKNAT3/4/5-like, from Medicago truncatula regulate legume nodule boundaries and shape development (Di Giacomo et al, 2017)
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