Expressed sequence tag analysis of Lilium longiflorum generative cells

The generative cell, the male gametic cell progenitor in flowering plants, undergoes mitotic division to produce two sperm cells. We have examined the gene expression profile of the Lilium longiflorum (lily) generative cell by sequencing expressed sequence tags (ESTs). A total of 886 ESTs derived from the generative cell cDNA library were clustered into 637 unique ESTs comprising 123 cluster ESTs and 514 singleton ESTs. Thirty-nine percent of non-redundant ESTs showing similarity to Arabidopsis genes with known function were thus assigned putative functions. Genes related to the ubiquitin system were abundant, suggesting the key role of ubiquitin-dependent proteolysis in gametogenesis. A total of 168 and 129 non-redundant lily generative cell ESTs showed significant similarity to maize sperm cell ESTs and Arabidopsis male gametophyte-specific transcripts, respectively. Fifty-five ESTs appeared to have significant similarities to both maize sperm cell ESTs and Arabidopsis male gametophyte-specific genes, indicating conservation of male gamete-expressed genes across different plant genera. Thus our data provide a handle to identify Arabidopsis gamete-expressed genes and to investigate their function. Several of these genes are potential candidates for analyzing the molecular basis of fertilization and for investigating mechanisms of gamete-specific transcriptional regulation in Arabidopsis through bioinformatics-based approaches.