The study of the regulation mechanism for exogenous auxin on root thickening based on transcriptome analysis in radish

Auxin is known to play a crucial role in governing storage root/tuber development, while the underlying mechanisms of its regulation on taproot thickening of radish have not yet been elucidated. In this study, exogenous auxin, Indole-3-acetic acid (IAA), and its transport inhibitor, 2,3,5-Triiodobenzoic acid (TIBA), were applied to seedlings of radish advanced inbred line, RB-203, on cortex split stage, and it was found that exogenous IAA and TIBA both significantly inhibited the radial growth of taproots and promoted its longitudinal growth. Exogenous IAA and TIBA both significantly increased endogenous IAA contents in the cambium zone compared with the control, which inhibited the normal differentiation of cambium cells and the enlargement of xylem cells, based on anatomical and hormonal analyses of taproots. Transcriptome analysis was conducted and Kyoto Encyclopedia of Genes and Genome pathway enrichment analysis revealed that differentially expressed genes were primarily involved in the alpha-Linolenic acid metabolism, biosynthesis of secondary metabolites, brassinosteroid biosynthesis, photosynthesis-antenna proteins and plant hormone signal transduction pathways. It was turned out that exogenous IAA significantly inhibited the expression of ARF5, which affected the division and differentiation of vascular cambium cells by regulating the expression of WOX4 and HD-ZIP III transcription factors, thus inhibiting taproot thickening of radish by further analyzing the DEGs involved in plant hormone signal transduction and the division and differentiation of vascular cambium mediated by auxin.