Figure 8.

Model of multi‐level response to DNA damage induced by Al.

Four different scenarios are compared that result in different plant phenotypes upon DNA damage. (a and b) DNA damage response (DDR) in wild‐type (WT) plants at low and high levels of DNA damage, respectively. (a) Already low levels of DNA damage presumably trigger a signalling cascade via ATR and SOG1 resulting in a full‐blown DDR that involves the induction of DNA repair genes as well as other responses, in particular the downregulation of cell proliferation activity. As a result, plant growth is reduced (green plant). Grey shaded plant indicates growth of a plant under conditions that do not damage DNA. (b) High levels of DNA damage give rise to even further reduced plant growth (green plant). Grey shaded plant indicates growth of a plant under conditions that do not damage DNA. (c and d) DDR in mutant plants at low and high levels of DNA damage. (c) Elimination of SOG1 and ATR can result in increased growth (green plant) in comparison to the WT (grey plant) under mildly DNA‐damaging conditions as long as DNA repair mechanisms [i.e. homology‐dependent repair (HR) pathways] remain functional. (d) During high levels of DNA damage, DNA repair alone is not sufficient anymore to sustain survival and growth, and the full repertoire of DDR is needed, for example, cell proliferation activities have to be adjusted. Grey shaded plant indicates the growth of a WT plant under these conditions. X indicates a yet to be identified upstream regulator that is postulated to act at a similar level as SOG1. Moreover, ATR and ATM appear to have different response thresholds for DNA damage, at least for the damage induced by Al. For details, see Discussion.