Unusual core histones specifically expressed in male gametic cells of Lilium longiflorum

We have cloned three novel histone genes using antibodies that recognize on ly nuclei of the male gametic (generative and sperm) cells of Lilium longif lorum. The deduced amino acid sequence of each clone shows only between 40% and 50% identity with the H2A, H2B and H3 somatic core histones of other p lant species. Transcripts of these genes were first detected in bicellular pollen soon after microspore mitosis, and their mRNAs, as revealed by in si tu hybridization, were observed only in the cytoplasm of the generative cel ls. As expression of these three genes was specific to generative cells wit hin the bicellular pollen, we designated the clones gH2A, gH2B and gH3. Imm unocytochemistry further revealed that the proteins encoded by these genes accumulated in the elongating and condensing generative nucleus during deve lopment of bicellular pollen, and were most abundant in the two sperm nucle i within an elongated pollen tube. We therefore propose that these male gam ete-specific core histones contribute to chromatin condensation of male gam etes or to chromatin remodeling, and result in the repression of gene expre ssion in male gametes.