Regulation of root meristem size in rice by cytokinins and ROS under salt stress

The root is a fundamental organ for plant nutrition, anchoring, and perception of soil-borne stresses. Root structure, influenced by genetic and environmental factors, is dynamic and modulated during plant growth in response to environmental conditions (plasticity). This plasticity is linked to the activity of the root apical meristem (RAM), regulated by hormones and reactive oxygen species (ROS) in Arabidopsis. Salinity inhibits root growth, reduces root hair density, and alters root system architecture, leading to biomass loss and decreased productivity. Given that rice is predominantly cultivated in coastal areas prone to salinization due to drought or flooding, understanding the molecular mechanisms governing RAM development and maintenance under salt stress is crucial for combating productivity loss. Our study leverages the conservation between Arabidopsis and rice RAM to translate knowledge across species. We identified similar mechanisms of meristem size determination. Imaging of the rice seminal root at the cellular level revealed that transition zone (TZ) positioning, and thus meristem size, is influenced by cytokinins, ROS, and high salinity. We observed parallels in the distribution of H2O2 and O2 -. Additionally, we identified homologous genes in rice, including PINs, RRs, and GH3s, which exhibited differential expression in response to cytokinins and H2O2. Comparing salt sensitive and salt-tolerant rice varieties, we found that tolerant plants maintained RAM size under stress by modulating cytokinin and auxin responses. In conclusion, our findings demonstrate that similar mechanisms regulate RAM size in rice and Arabidopsis, providing a foundation for understanding rice root plasticity under high salinity conditions—a major threat to global rice productivity. This work was supported by the grant 2022NZ7M3W from Unione europea- Next Generation EU, Missione 4 Componente 1 CUP C53D23003140001