Transcriptome profiling of Lilium longiflorum generative cells by cDNA microarray

The generative cell, which is produced by asymmetric division of the unicellular microspore, undergoes further mitotic division to produce two sperm cells that take part in double fertilization. Expressed sequence tag (EST) analysis of Lilium longiflorum (lily) generative cell cDNA library has shown that a diverse complement of genes is transcribed in these cells. Here we address the cell specificity of genes expressed in lily generative cell by using spotted cDNA microarray. Microarray slides were hybridized with labeled probes prepared from transcripts originating from generative cells and other tissues (mature pollen, uninucleate microspore, ovary, root tip, and shoot). The hierarchical clustering revealed that 356 of 430 gene transcripts (83%) of generative-cell genes were up regulated in generative cells. Thirty-eight percent of generative-cell-enriched transcripts were assigned their putative functions, with an abundance of genes involved in protein destination and signal transduction. These results suggest that the expression of a subset of flowering plant genes is tightly controlled and up-regulated in generative cells in order to implement their specialized function. These data thus represent a significant increase in the genes identified as being up-regulated in generative cells and would allow functional analysis of a large number of flowering plant male gamete expressed genes.