In the realm of the homeodomain

Isolation and characterization of genes associated to cotton somatic embryogenesis by suppression subtractive hybridization and macroarray

Somatic embryogenesis (SE) is the developmental reprogramming of somatic cells toward the embryogenesis pathway and is a notable illustration of cell totipotency. To identify genes involved in SE, subtractive polymerase chain reaction (PCR) was performed to generate transcripts highly enriched for SE-related genes, using cDNA prepared from a mixture of embryogenic callus and pre-globular somatic embryos, as the tester, and cDNA from non-embryogenic callus, as the driver. After differential screening and subsequent confirmation by reverse Northern blot analysis, a total of 671 differentially expressed cDNA fragments were identified, and 242 uni-genes significantly up-regulated during cotton SE were recovered, as confirmed by Northern blot and reverse-transcription PCR analysis of representative cases, including most previously published SE-related genes in plants. In total, more than half had not been identified previously as SE-related genes, including dominant crucial genes involved in transcription, post-transcription, and transportation, and about one-third had not been reported previously to GenBank or were expected to be unknown, or newly identified genes. We used cDNA arrays to further investigate the expression patterns of these genes in differentiating gradient culture, ranging from pro-embryogenic masses to somatic embryos at every stage. The cDNA collection is composed of a broad repertoire of SE genes which is an important resource for understanding the genetic interactions underlying SE signaling and regulation. Our results suggested that a complicated and concerted mechanism involving multiple cellular pathways is responsible for cotton SE. This report represents a systematic and comprehensive analysis of genes involved in the process of somatic embryogenesis.

Identification of a homeobox-containing gene with enhanced expression during soybean (Glycine max L.) somatic embryo development

Homeotic gene are key 'switches' that control developmental processes. Homeotic genes containing the consensus 'homeobox' domain have been identified from a number of organisms including Drosophila melanogaster, Caenorhabditis elegans, Homo sapiens, and Zea mays. Although homeotic genes have been demonstrated to be important in embryo development of some insects, amphibians, and mammals, there are no reports of their involvement in plant embryogenesis. Here, we report the isolation and characterization of a cDNA clone for a homeobox-containing gene expressed in somatic embryos of soybean. The cDNA (Sbh1 for soybean homeobox-containing gene) was isolated using maize Knotted-1 (Kn1) cDNA as a heterologous probe. The Sbh1 cDNA clone is 1515 bp long which is the approximate size of its transcript. Within the homeodomain, the amino acid sequence of a helix-turn-helix structure, and invariant and conserved residues were identified. The deduced SBH1 protein shares a high amino acid identity with KN1 protein (47.0% overall and 87.5% for the homeodomain). Southern hybridization analysis indicated that Sbh1 is a member of a small gene family. The expression of Sbh1 is development- and tissue-specific. The transcript of Sbh1 was present in early-stage somatic embryos, increased prior to cotyledon formation and decreased thereafter. Sbh1 was weakly expressed in soybean stems and hypocotyl but was not detected in other plant tissues and nonembryogenic materials. The enhanced expression during embryogenesis, the homology with maize Kn1 gene, and the regulatory nature of homeodomain proteins suggest that the SBH1 protein plays an important role in plant embryo development.