Plants, like animals, typically reproduce via contributions from both male and female organisms. However, scientists have observed asexual plant reproduction, known as parthenogensis or apomixis, for centuries. Now a team of German and Israeli researchers has identified the gene that triggers reproduction without sex in the moss Physcomitrella patens.
Mosses, like all bryophytes, have two distinct life stages: the gametophyte, which produces eggs and sperm, and the sporophyte, formed by the fertilization of the egg by the sperm. Gametophyte cells are typically haploid, having only one set of chromosomes, and sporophyte cells are typically diploid, having two sets of chromosomes.
Plant biotechnologist Ralf Reski and his student Nelly Horst at the University of Freiburg, along with biologist Nir Ohad at Tel Aviv University and other colleagues, suspected that the BELL family of genes, which are known to regulate sporophyte development in flowering plants, may be involved in asexual reproduction. They focused on BELL1, noting that its proteins accumulated in female but not male sexual organs of P. patens, and only during certain phases of reproduction, which suggested that this gene might regulate development in the egg.
The team used genetic engineering to first develop plants lacking the BELL1 gene. They found that these mutants developed similarly to unaltered plants except that the egg cells were larger and the plants never developed sporophytes, confirming the importance of BELL1 in reproduction.
The researchers then developed plants in which the BELL1 gene was overexpressed, meaning the plants created more BELL1 proteins than normal. These plants spontaneously and without fertilization developed structures resembling embryos, which developed into functional sporophytes. The diploid sporophytes then produced spores nearly identical to those of the unchanged plants that reproduced via fertilization.
These results suggest that BELL1 controls the transition from gametophyte to sporophyte in P. patens. The finding not only sheds light on how land plants evolved from freshwater algae roughly 500 million years ago, but also may be useful in crop breeding programs where increased production of genetically identical plants is desirable. (Nature Plants)