Isolation of two genes that were induced upon the initiation of somatic embryogenesis on carrot hypocotyls by high concentrations of 2,4-D

This study describes the formation of somatic embryos directly on the surfa ce of hypocotyl sections of Daucus carota L. after exposure to 450 mu M of 2,4-D for 2 h, followed by culturing without 2,4-D for 2 weeks. A search fo r differentially expressed genes immediately after the 2,4-D treatment resu lted in the identification of two genes, Dchsp-1 and Dcarg-1. Dchsp-1 has h omology to low-molecular-weight heat-shock proteins, while Dcarg-1 has homo logy to auxin-regulated genes. Dchsp-1 was expressed upon the exposure to 2 ,4-D treatment but also responded to general stress responses. Dcarg-1 resp onded primarily to auxin; however, a parallel relationship between the expr ession of Dcarg-1 and the formation of somatic embryos on the hypocotyl sec tions was observed. It seems the exposure to auxin shock could serve as a t rigger in inducing cell division in the epidermal cells and promoting their further differentiation to somatic embryos. These results are discussed in relationship to our current understanding of the molecular basis of somati c embryogenesis.