DNA damage inhibits root growth by enhancing cytokinin biosynthesis in Arabidopsis thaliana.

Plant root growth is influenced by external factors to adapt to changing environmental conditions. However, the mechanisms by which environmental stresses affect root growth remain elusive. Here we found that DNA double-strand breaks (DSBs) induce the expression of genes for the synthesis of cytokinin hormones and enhance the accumulation of cytokinins in the Arabidopsis root tip. This is a programmed response to DSBs through the DNA damage signaling pathway. Our data showed that activation of cytokinin signalling suppresses the expression of PIN-FORMED genes that encode efflux carriers of another plant hormone, auxin, thereby disturbing downward auxin flow and causing cell cycle retardation in the G2 phase. Elevated cytokinin signalling also promotes an early transition from cell division to endoreplication, resulting in a reduction of the root meristem size. We propose that in response to DNA stress, plants inhibit root growth by orchestrating hormone biosynthesis and signalling.