We identified IAA13 negatively associated with lateral root number by comparing the differential expressed genes between Bupleurum chinense and B. scorzonerifolium. Dried roots of the genus Bupleurum L. are used as a herbal medicine for diseases in Asia. Bupleurum chinense has a greater number of lateral roots than B. scorzonerifolium, but the genetic mechanisms for such differences are largely unknown. We (a) compared the transcriptome profiles of the two species and (b) identified a subset of candidate genes involved in auxin signal transduction and explored their functions in lateral root development. By isoform sequencing (Iso-Seq) analyses of the whole plant, more unigenes were found in B. scorzonerifolium (118,868) than in B. chinense (93,485). Given the overarching role of indole-3-acetic acid (IAA) as one of the major regulators of lateral root development, we identified 539 unigenes associated with auxin signal transduction. Fourteen and 44 unigenes in the pathway were differentially expressed in B. chinense and B. scorzonerifolium, respectively, and 3 unigenes (LAX2, LAX4, and IAA13) were expressed in both species. The number of lateral root primordia increased after exogenous auxin application at 8 h and 12 h in B. scorzonerifolium and B. chinense, respectively. Since overexpression of IAA13 in Arabidopsis reduced the number of lateral roots, we hypothesized that IAA13 is involved in the reduction of the number of lateral roots in B. scorzonerifolium.
Keywords: Auxin signal transduction; Bupleurum; Lateral roots; Transcription factors; Transcriptome analysis.