ORIGINAL ARTICLE Shibo Zhang Laurie Wong Ling Meng Peggy G. Lemaux Similarity of expression patterns of knotted1 and ZmLEC1 during somatic and zygotic embryogenesis in maize (Zea mays L.) Received: 21 August 2001 / Accepted: 14 December 2001 / Published online: 20 March 2002 Ó Springer-Verlag 2002 Abstract Expression of knotted1 (kn1) and ZmLEC1,a maize homologue of the Arabidopsis LEAFY COTY- LEDON1 (LEC1) was studied using in situ hybridiza- tion during in vitro somatic embryogenesis of maize (Zea mays L.) genotype Hi-II. Expression of kn1 was initially detected in a small group of cells (5–10) in the somatic embryo proper at the globular stage, in a spe- cific region where the shoot meristem is initiating at the scutellar stage, and specifically in the shoot meristem at the coleoptilar stage. Expression of ZmLEC1 was strongly detected in the entire somatic embryo proper at the globular stage, gradually less in the differentiating scutellum at the scutellar and coleoptilar stages. The results of analyses show that the expression pattern of kn1 during in vitro somatic embryogenesis of maize is similar to that of kn1 observed during zygotic embryo development in maize. The expression pattern of ZmLEC1 in maize during in vitro development is similar to that of LEC1 in Arabidopsis during zygotic embryo development. These observations indicate that in vitro somatic embryogenesis likely proceeds through similar developmental pathways as zygotic embryo develop- ment, after somatic cells acquire competence to form embryos. In addition, based on the ZmLEC1 expression pattern, we suggest that expression of ZmLEC1 can be used as a reliable molecular marker for detecting early- stage in vitro somatic embryogenesis in maize. Keywords Gene expression kn1 Somatic embryogenesis (in vitro) Zea (embryogenesis) ZmLEC1 Zygotic embryogenesis Abbreviations 2,4-D: 2,4-dichlorophenoxyacetic acid DIG: digoxigenin Introduction Somatic embryogenesis is one of the two plant devel- opmental pathways by which somatic embryos are induced from in vitro-cultured somatic cells or tissues (Thorpe 1994). This in vitro phenomenon was first observed in freely suspended cells of carrot in 1958 (Steward et al. 1958) and then in a culture derived from carrot roots as explants (Reinert 1959). While carrot was the first plant species in which somatic embryogenesis was reported, during the last 40-plus years of culturing experiments the induction of in vitro somatic embryo- genesis has been shown to be successful in many plant species, including angiosperms and gymnosperms. Now, in vitro somatic embryogenesis is widely employed to produce genetically transformed plants. Historically, it has been observed that there are ge- netic and also physiological factors that trigger in vitro embryogenesis in various types of plant somatic cells. However, the molecular bases of those triggering factors and the genetic and biochemical mechanisms leading to in vitro embryogenesis are still unknown. In the last 10 years, genetic and molecular studies of plant devel- opment have resulted in the identification of many critical genes that are either involved in or regulate in vivo plant development. Maize knotted1 (kn1) was the first homeobox gene identified in plants (Vollbrecht et al. 1991) and is critical in maintaining shoot meristems in an undifferentiated state (Kerstetter et al. 1997). Ex- pression of kn1 during zygotic embryo development of maize is detected as early as 10 days after pollination (Smith et al. 1995). The Arabidopsis gene, LEAFY COTYLEDON1 (LEC1), encodes a transcription factor homologue, the CCAAT box-binding factor HAP3 subunit, and func- tions at an early developmental stage to maintain em- bryonic cell fate (Lotan et al. 1998). The mRNA of LEC1 was detected in embryo cell types and in endo- sperm tissue during embryo development. Ectopic post- embryonic expression of LEC1 is able to induce the Planta (2002) 215: 191–194 DOI 10.1007/s00425-002-0735-3 S. Zhang L. Wong L. Meng P.G. Lemaux (&) Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA E-mail: lemauxpg@nature.berkeley.edu Fax: +1-510-6427356