Comparative spatial transcriptomics reveals root dryland adaptation mechanism in rice and HMGB1 as a key regulator.

Drought severely threatens food security, and its detrimental effects will be exacerbated by climate change in many parts of the world. Rice production is water-consuming and particularly vulnerable to drought stress. Upland rice is a special rice ecotype that specifically adapts to dryland mainly due to its robust root system. However, the molecular and developmental mechanism underlying this adaption has remained elusive. In this study, by comparing the root development between upland and irrigated rice phenotypically and cytologically, we identified key developmental phenotypes that distinguish upland rice from irrigated rice. We further generated spatial transcriptomic atlases for coleoptilar nodes and root tips to explore their molecular differences in crown root formation and development, uncovering promising genes for enhancing rice drought resistance. Among the identified genes, HMGB1, a transcriptional regulator, functions as a key factor that facilitates root elongation and thickening in upland rice and thereby enhances drought resistance. In summary, our study uncovers spatially resolved transcriptomic features in roots of upland rice that contribute to its adaptation to dryland conditions, providing valuable genetic resources for breeding drought-resilient rice.