Transcriptional activity of male gamete-specific histone gcH3 promoter in sperm cells of Lilium longiflorum

Abstract

Histones are essential for packaging of eukaryotic genomic DNA in nucleosomes, and histone gene expression is normally coupled with DNA synthesis. Some of the flowering plant histone genes show strictly male gamete-specific expression. However, mechanisms underlying their male gamete-specific expression have not been elucidated so far. Here we report the isolation of the male gamete-specific histone gcH3 promoter from Lilium longiflorum and its activity in the male gametic cell of the flowering plant. The OCT motif, which is well conserved in plant histone promoters regulating S phase-specific expression, is not conserved in the gcH3 promoter. Instead sequence motifs identical to GC box 1 and GC box 2, the transcriptional activator and suppressor for mammalian testis-specific histone H1t, are present in the gcH3 promoter, suggesting that plants and animals share the mechanism which governs the specificity of gene expression in male gametic cells. Male gamete-specific activation of the gcH3 promoter has been confirmed by microprojectile bombardment in lily pollen. The sperm cell carrying gold particles showed reporter gene expression, while green fluorescent protein (GFP) was absent in the other sperm cell which had no particles, confirming that the gcH3 promoter is activated in the male gametic cell, and sperm cells have transcriptional and translational machinery that is independent of the vegetative cell of pollen.