Initiation of scutellum-derived callus is regulated by an embryo-like developmental pathway in rice

In rice (Oryza sativa) tissue culture, callus can be induced from the scutellum in embryo or from the vasculature of non-embryonic organs such as leaves, nodes, or roots. Here we show that the auxin signaling pathway triggers cell division in the epidermis of the scutellum to form an embryo-like structure, which leads to callus formation. Our transcriptome data show that embryo-, stem cell-, and auxin-related genes are upregulated during scutellum-derived callus initiation. Among those genes, the embryo-specific gene OsLEC1 is activated by auxin and involved in scutellum-derived callus initiation. However, OsLEC1 is not required for vasculature-derived callus initiation from roots. In addition, OsIAA11 and OsCRL1, which are involved in root development, are required for vasculature-derived callus formation but not for scutellum-derived callus formation. Overall, our data indicate that scutellum-derived callus initiation is regulated by an embryo-like development program, and this is different from vasculature-derived callus initiation which borrows a root development program.