Genome-wide analysis of gene expression in the soybean shoot apical meristem

The shoot apical meristem (SAM) contains undifferentiated stem cells that are responsible for the initiation of above-ground organs, and eventually the general architecture of the plant. To gain insight into the nature of genetic programs and the regulatory networks underlying SAM function in soybean, we have used Affymetrix soybean GeneChip® to investigate the transcript profiles associated with micro-dissected SAMs or axillary meristems (AMs). While the microarray data disclosed the conservation of transcriptional signature between the two types of meristems, subsequent comparison of SAM transcript profile with that of non-meristem (NM) tissue revealed a total of 1090 and 1523 transcripts that are significantly up- or down-regulated in the SAM. Further in situ hybridization analysis on selected transcripts has implicated their roles in SAM maintenance and the establishment of organ polarity. We also identified a gene that could potentially serve as a novel marker that distinguishes the differentiating cells in the meristem from the pluripotent stem cells. Along with many unknowns, transcripts with putative annotation have also been identified that has allowed us to infer SAM regulatory roles for various families of transcription factors as well as products associated with auxin-mediated responses, cell division and proliferation, epigenetic regulation, miRNA regulation and protein turnover. Computational analysis on the promoter regions of Arabidopsis orthologs of genes with high expression in the soybean SAM revealed a conserved over-representation of three cis-acting regulatory motifs. Our microarray data thus represents a rich source of target genes for further study into the meristem function and maintenance. Keywords: meristem transcript profile A total of six microarray hybridization experiments were performed to obtain transcript profiles of the three tissues with the incorporation of two independent biological replicates.