|Mcgrath, J Mitchell - Mitch|
Submitted to: Plant Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/1997
Publication Date: N/A
Interpretive Summary: Pollen carries genes from the male parent to the seed parent in flowering plants. How these genes are packaged in pollen has been difficult to determine because each pollen grain contains two types of nuclei, a pollen (sperm) nucleus which conveys the genetic material and vegetative nuclei which function during pollen tube growth. In animals, sperm have a single nucleus and the organization of genes within sperm is known to be different than in other types of nuclei. The objective of this research was to examine sperm from ferns, a group of non-flowering plants with close affinities to flowering plants. Fern sperm cells are free-swimming and have a single nucleus. DNA was readily isolated from fern sperm cells and the DNA was examined for a particular modification that is often associated with inactive genetic material. The results showed that fern sperm DNA is highly modified and the pattern of modification appears different from fern vegetative cells. Each of these observations suggests fern sperm are passive carriers of genetic material. The concept of using DNA from fern sperm cells reported here will have a substantial impact on furthering our understanding of the organization of genetic material in plant reproductive cells. A better understanding of plant genetic material is necessary for plant breeders and other biologists to meet the increasing challenges of agriculture for the future.
Technical Abstract: Plants, in general, have a high proportion of their CpG and CpNpG nucleotide motifs modified with 5-methylcytosine (5mC). Developmental changes in the proportion of 5mC are evident in mammals, particularly during gametogenesis and embryogenesis, but little information is available from flowering plants due to the intimate association of gametes with sporophytic tissues. In ferns, sperm are uninucleate and free-swimming and thus are easily isolated. We have examined 5mC in DNA isolated from fern sperm and other tissues with methylation-sensitive and -insensitive restriction enzyme isoschizomers, Southern blots probed with chloroplast and nuclear ribosomal RNA genes and end-labeled restriction fragments. We conclude that fern sperm DNA is methylated to a similar or greater degree than DNA isolated from either sporophytes or gametophytes