Functional divergence of RrGL3 and RrEGL3 from Rosa roxburghii in mediating trichome development

The basic helix-loop-helix (bHLH) proteins GL3 (GlABRA 3) and EGL3 (Enhancer of GLABRA 3) are transcription factors that establish physical interactions with GL1 and TTG1 to regulate trichome development in Arabidopsis. In this study, we identified GL3 and EGL3 homologous genes from Rosa roxburghii, named RrGL3 and RrEGL3, respectively. RrGL3 and RrEGL3 were both exclusively localized in the nucleus. Transcriptional profiling and in situ hybridization demonstrated that the expression level of RrEGL3 was significantly higher than RrGL3 in vegetative and reproductive tissues. Moreover, RrEGL3 was remarkably expressed in flower buds and the prickles of young fruits. Notably, overexpression of RrEGL3 produced significantly more trichomes compared with wild type. Besides, RrEGL3 was able to functionally complement the glabrous phenotype of gl3 egl3 and ttg1 mutants. Surprisingly, overexpression of RrGL3 did not influence trichome patterning in Arabidopsis. Finally, while RrEGL3 was found to interact with both TTG1 and GL1 in vitro and in vivo, in contrast, RrGL3 only interacted with GL1. The inability of RrGL3 to interact with TTG1 suggests functional divergence between RrGL3 and RrEGL3. These results illustrated that highly expressed RrEGL3 mediates trichome development in Arabidopsis by forming a GL1-RrEGL3-TTG1 complex, proposing RrEGL3 as a good candidate for controlling prickles in R. roxburghii. This study provides insights into the molecular mechanisms concerning the development of prickles in the Rosaceae family, and provides the theoretical basis for cultivation of prickle-free fruits. RrEGL3 expressed highly in tissues presenting prickles of Rosa roxburghii could mediated trichome development in Arabidopsis by forming GL1-RrEGL3-TTG1 complex.