YUKIKO MIZUKAMI

Research from my group at Purdue is focused to investigate the regulatory mechanisms and roles of endoreduplication in cell differentiation.

During plant and animal organogenesis, an increase of nuclear size occurs in certain types of cells. This increase is the result of endoreduplication, an alternative cell cycle that replicates genome DNA, completely or partially, without nuclear and cell divisions. Not only developmental cues, but also external abiotic or biotic signals such as nutritional supply or pathogenic/symbiotic microbial infection trigger endoreduplication whose progression is tightly associated with cell differentiation and cell morphogenesis. As endoreduplication proceeds, increase in cell size is positively correlated to nuclear size (i.e., levels of endoploidy or DNA content) and exhibit subsequent morphological and metabolic alterations. Previous studies suggest that endoreduplication likely evolved as a strategy to alter nuclear size and thereby regulate gene expression of differentiating cells in response to developmental or external signals. However, little is known about developmental control of endoreduplication. What developmental and molecular mechanisms trigger, maintain, and terminate endoreduplication? Does endoreduplication result in both quantitative and qualitative alterations of gene expression? How does endoreduplication participate in cell growth, differentiation, metabolism, and susceptibility to abiotic and biotic stresses? The ultimate goal of our research project is to understand 1) the mechanisms that control endoreduplication in differentiating cells and 2) the links between endoploidy levels and cell growth, cell differentiation, and cellular activity.

To address this long-term goal, my research group at Purdue is investigating key regulators of endoreduplication and establishing genetic materials and molecular tools by which the cell cycle switch to endoreduplication can be manipulated in plants. We use the model plant Arabidopsis thaliana, which has a small, diploid genome that has been completely sequenced and therefore is an excellent system for applying molecular, genetic and bioinformatics approaches. We have identified several genes that are key regulators of endoreduplication. Using these novel tools, we will explore the developmental, genetic, and molecular mechanisms and roles of endoreduplication control in plant cell differentiation. We anticipate that the manipulation of endoreduplication in targeted plant tissues or cells is a novel method for controlling differentiation, patterning, metabolism, and external stress tolerance, and therefore, useful for increasing plant biomass and productivity.