Luciferase assay
pDR5:Lucifease expression along the primary root was analyzed by using Lumazon (Wei Xuan, Opdenacker, Vanneste, & Beeckman, 2018). After 6-8 d of co-cultivation, pDR5:Lucifease plants were sprayed with a 1mM potassium luciferin (Gold Biotechnology) and reacted for 15 min in darkness, then imaged immediately with a 15 min exposure time. For investigating the effects of SQR9 VCs on the periodicity of DR5oscillation, the position of root tip was marked after 4 d of co-cultivation and the prebranch sites formed in the following 2 d (48h) was counted. The picture series were saved as TIFF format by IVScopeEQ software for further analysis in Fiji (http://fiji.sc/). The Fiji lookup tables ”Fire” was used to convert black and white images into color scales based on pixel intensity.