Association of auxin, cytokinin, abscisic acid, and plant peptide response genes during adventitious root formation in Marubakaido apple rootstock (Malus prunifolia Borkh. var. ringo Asami)

In this study, changes in gene transcription during adventitious root formation in hardwood cuttings of Marubakaido apple rootstock were examined by RNA-seq analysis. In line with above, 11 genes related to root development were identified as candidate genes for modulator of adventitious root formation. Among them, the induction of ABC transporter G family member-, NO VEIN-, and Auxin transporter-like protein 2-like genes, which are known to be associated with cellular auxin distribution and maintenance of root meristem niche, before the appearance of the first visible adventitious root formation in Marubakaido was revealed by quantitative RT-PCR. In addition, we conducted comprehensive co-expression network and MAPMAN analysis, and found a relationship between adventitious root formation and phytohormones such as cytokinin and abscisic acid (ABA). Finally, we also found the genes encoding receptor of plant peptide hormone, such as Barely any meristem 3-like gene (a receptor of plant peptide hormone CLAVATA45) and phloem intercalated with xylem-like gene (a receptor of the plant peptide hormone known as tracheary element differentiation inhibitory factor or TDIF), assuming the association of plant peptide hormone with adventitious root formation in Marubakaido apple rootstock. CLAVATA and TDIF are known as plant peptide hormones related to root stem cell and vascular differentiation, respectively. Therefore, we conclude that the process of adventitious root formation such as the maintenance of stem cell and vascular differentiation in Marubakaido apple rootstock was controlled by complex plant hormone signalling, including auxin, cytokinin, ABA, and plant peptide hormone.