Hosted by: Winslow Briggs
DNA double strand breaks (DSBs) are perceived by all cells and trigger a variety of responses. In animals, the persistence of DSBs is essentially employed as a proxy for the induction of cancer-promoting mutations (as mutations per se cannot be detected). Cells carrying a threshold level of DSBs are destroyed via a programmed response that clearly contributes to tumor suppression. In contrast, in the plant Arabidopsis, UV- and ionizing radiation (IR)-induced programmed cell death is limited to a handful of stem cells in the stem cell niche of the meristematic zone. I will discuss the biological significance of this cell-type specific response to DNA damage. We found that the irradiated root tip actively destroys the stem cell niche, and then rebuilds the root apical meristem through transdifferentiation of surviving, surrounding cells. In contrast, irradiated sog1-/- mutants, defective in transcriptional response to radiation, maintain root apical meristem organization and cell identity for several days, after which the meristematic structure (and the potential for growth) of the arrested root tip is lost in what appears to be “normal” progressive basipetal differentiation. We speculate that the PCD response to DNA damage, in plants, is essentially a developmental response, rather than a response that evolved to prevent cancer. This response may have evolved in land plants in order to rescue root and shoot meristems from the double strand break-inducing effects of desiccation.