Comparative transcriptomics of lowland rice varieties leads to novel candidate genes for adaptive iron excess tolerance.

Iron (Fe) toxicity is a major challenge for plant cultivation in acidic water-logged soil environments, where lowland rice is a major staple food crop. Only few studies addressed the molecular characterization of excess Fe tolerance in rice, and these highlight different mechanisms for Fe tolerance. Out of 16 lowland rice varieties we identified a pair of contrasting lines, Fe-tolerant Lachit and -susceptible Hacha. The two lines differed in their physiological and morphological responses to excess Fe, including leaf growth, leaf rolling, reactive oxygen species generation, Fe and metal contents. These responses were likely of genetic origin as they were mirrored by differential gene expression patterns, obtained through RNA-sequencing, and corresponding GO term enrichment in tolerant versus susceptible lines. 35 genes of the metal homeostasis category, mainly root-expressed, showed differential transcriptomic profiles suggestive of an induced tolerance mechanism. 22 out of these 35 metal homeostasis genes were present in selection sweep genomic regions, in breeding signatures and/or differentiated during rice domestication. These findings suggest that Fe excess tolerance is an important trait in the domestication of lowland rice, and the identified genes may further serve to design targeted Fe tolerance breeding of rice crops. © The Author(s) 2021. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists.