How plant cells sense and repond to gravityMari Salmi, grad student in Dr. Stan Roux's lab
I am working in Dr. Stan Roux's lab for my PhD dissertation project. The overall topic of my project is studying the mechanism by which a single plant cell senses and responds to gravity. The single cell that we use, as a model system for studying plant gravity responses is the spore of the aquatic fern Ceratopteris richardii. The germination of the spore begins when it is exposed to both light and water, and is considered complete when the root-like rhizoid emerges through the spore coat. Gravity fixes the polarity of the cell, i.e. which direction the rhizoid will emerge, within the first 20 hours after light exposure.
Ceratopteris Spore Development
About 72 hours after spores are initially exposed to light, the primary rhizoid begins to emerge from the spore coat. On earth the primary rhizoid emerges downward in more than 95% of spores. Ceratopteris spores were flown on NASA payload flight STS-93, and spores germinating in microgravity on the space shuttle had rhizoids emerge in random orientations. Part of my dissertation project is to evaluate difference in gene expression between those spores that germinated randomly in microgravity and spores that germinate on earth in 1 g with their rhizoid emerging downward.
I have constructed a cDNA microarray with over two thousand different Ceratopteris genes to evaluate these changes in gene expression. With a cDNA microarray the level of expression of genes in one population (in my case, spores developing at 1 g) can be quantitatively compared to the level of expression of those genes in another population (microgravity developing spores). All of the genes printed on the array can be simultaneously compared. Once I have determined several genes whose expression pattern varies between germination on earth and germination in space, I will further investigate the role of several of these genes in the spores gravity directed development by “knocking out” the expression of the gene. This study will begin to identify genes involved early in the signaling of a plant gravity response.