STO and GA negatively regulate UV-B-induced Arabidopsis root growth inhibition.

Studies on UV-B-induced plant photomorphogenesis mainly focus on Arabidopsis shoots (hypocotyl, leaf, petiole, and stem) but less on roots. In the present research, the low-level UV-B (0.2 W·m-2) induced a decrease in the number of root cells in the meristem zone and an inhibition of the cell length in the maturation zone of roots in Arabidopsis thaliana L.Heynh (Col-0). UV-B-induced root growth inhibition was recovered by the addition of GA3 to culture media. GA3 played an important role in UV-B-induced inhibition of root growth. The cop1-4 mutant with more meristem cell and longer mature cells exhibited longer root length under low-level UV-B. COP1 acted as a positive regulator of root growth under UV-B, through regulation of cell division and elongation. The sto mutant exhibited a shorter root length under UV-B with similar cell length but fewer meristem cells compared with wild type (Col-0). STO only regulated cell division, but cell expansion was not affected. UV-B radiation also inhibited the root growth of uvr8 mutant, and the degree of inhibition was greater than for wild type (Ler). UV-B inhibited the growth of Arabidopsis root, possibly because it changes the GA signal and inhibited cell division and cell elongation, which be related to COP1 and STO genes.