GIS mediates GA signaling to directly target the expression of SPL15 to regulate trichome development in Arabidopsis thaliana.

Trichome development in Arabidopsis thaliana is regulated by a complex network of genetic and hormonal signaling pathways. GA/DELLA/GISs and miR156/SPLs are the two main regulatory modules regulating trichome initiation in A. thaliana. However, it is not clear whether there is an interaction between them. Furthermore, GIS was the first gene in the GIS family to be identified as regulating trichome development through GA signal in A. thaliana. Nevertheless, how GIS regulates trichome development through GA signal is still unknown. In this study, we first illuminated that GIS could directly target the expression of SPL15 to regulate trichome development through GA signal. Our results showed that the loss of SPL15 function significantly increases trichome density, whereas its overexpression suppresses trichome formation. Moreover, exogenous GA treatment promotes trichome development in the SPL15 overexpressing lines. More importantly, molecular and genetic studies revealed that GIS acts upstream of SPL15 by binding to its promoter to regulate the trichome development in A. thaliana. These indicate that C2H2 transcriptional factor GIS may be the key bridge gene connecting miR156/SPLs and GA/DELLA/GIS modules to regulate trichome development in A. thaliana. These results reveal a novel pathway, GA-GIS-SPL15, to regulate trichome development through the GA pathway and extend our knowledge of the GA-GIS-SPL15 regulating network.