Effect of NJ15 on gene expression profiles in Arabidopsis thaliana seedlings

Brassinosteroid (BR) and auxin co-regulate plant growth in a process termed cross-talking. Based on the assumption that their signal transductions are partially shared, inhibitory chemicals for both signal transductions were screened from a commercially-available library. A chemical designated as NJ15 (ethyl 2-[5-(3,5-dichlorophenyl)-1,2,3,4-tetrazole-2-yl]acetate) diminished the growth promotion of both adzuki bean epicotyls and Arabidopsis seedlings, by either the application of BR or auxin. To understand its target site(s), bioassays with a high dependence on either the signal transduction of BR (BR-signaling) or of auxin (AX-signaling), were performed. NJ15 inhibited photomorphogenesis of Arabidopsis seedlings grown in the dark, which mainly depends on BR-signaling, while NJ15 also inhibited their gravitropic responses mainly depending on AX-signaling. On the study for the structure-activity relationships of NJ15 analogues, they showed strong correlations on the inhibitory profiles between BR- and AX-signalings. These correlations imply that NJ15 targets the downstream pathway after the integration of BR- and AX-signals. Arabidopsis thaliana ecotype Col-0 was used as the wild type (WT) in this study. The Col-0 plants, grown vertically as a gravitropic response assay for 4 days on MS plates, were sprayed with mock or with 10 µM NJ15 (ethyl 2-[5-(3,5-dichlorophenyl)-1,2,3,4-tetrazole-2-yl]acetate) and were gravistimulated by turning then 90° relative to the first direction. After 8 h, plants were harvested and total RNA was extracted with a Total RNA Extraction Kit Mini for plant (RBC Bioscience), then total RNA was subjected to microarray analysis.