Combination of teg1 and our1 enhances total root length through preferential carbon allocation to lateral root growth...

Root system development is essential for water and nutrient acquisition but requires substantial carbon investment. Optimizing root architecture while minimizing carbon costs is therefore an important target for crop improvement. Here, we characterized a novel rice (Oryza sativa L.) mutant, truncated elongation growth 1 (teg1), which exhibits reduced seminal and crown root elongation but enhanced lateral root development. Histological analyses revealed that the shortened root phenotype was associated with reduced root apical meristem activity and decreased cell elongation. Rice possesses different lateral root types, with L-type lateral roots being thicker and capable of branching into smaller lateral roots, and S-type lateral roots being thinner and shorter than L-type lateral roots. Despite shorter seminal and crown roots, teg1 developed a higher density of L-type lateral roots and longer L-type lateral roots than the wild type. To investigate the interaction between root architecture and carbon allocation, teg1 was combined with the outstanding rooting 1 (our1) mutation, which promotes seminal, crown and lateral root elongation. The teg1 our1 double mutant exhibited increased L-type lateral root growth accompanied by reduced seminal and crown root growth while maintaining total root length. Carbon-14 tracer analysis revealed enhanced accumulation of newly assimilated carbon in elongating L-type lateral roots of the double mutant. Furthermore, the root-to-shoot dry weight ratio of the double mutant remained comparable to that of the wild type. These results suggest that teg1 promotes compensatory lateral root development and alters carbon allocation within the root system, providing a potential genetic resource for improving root system architecture in rice.