mutation alleviates DNA damage in an mutant sensitive to excess boron.

Excess boron (B) is toxic to plants and thereby causes DNA damage and cell death in root meristems. However, the underlying mechanisms which link boron and DNA damage remain unclear. It has been reported that the mutant of the 26S proteasome is sensitive to excess boron, resulting in more frequent cell death in root meristem and reduced root elongation. In this study, we showed that a reduction in root growth in the mutant in the presence of high boron levels is repressed by a mutation in NAC domain containing transcription factor NAC103, a substrate of the proteasome, which functions in the unfolded protein response pathway. The mutation in NAC103 alleviated excess-B-induced DNA damage and cell death in root meristems of the mutant. Superoxide ( ) staining with nitroblue tetrazolium revealed that boron stress causes accumulation in root tips, which was higher in the mutant, whereas the accumulation was lower in the double mutant. Our work demonstrates the overall involvement of in maintaining healthy root meristem under excess boron conditions in the absence of proteasome subunit.