Functional Analysis of a Mutation Promoting Lateral Root Development via Carbohydrate Regulation in Rice
The root system comprised largely of lateral roots (LRs) is a major determinant of water and nutrient acquisition for growth and development as well as stress adaptability to dynamically fluctuating environmental soil conditions. In our study, a rice mutant with enhanced LR development under non-stress condition was screened although such phenotype is usually observed under stress condition. Additionally, the mutant displayed lower starch stain level in the stem, which pointed us to the possible involvement of carbohydrates in the observed mutant root phenotype. Furthermore, our previous evaluation of the mutant in N conditions showed that it could respond to the availability of N by increasing the number and length of LRs with thicker diameter along with the significant decrease of starch level in the leaf sheath, which may suggest the utilization of carbohydrates for more developed LRs. While the consumption of carbohydrates for LRs under N may not always be beneficial for plant productivity, we hypothesized that such phenotype may be more functional in facilitating maintained root system development and water uptake that may contribute to maintained shoot dry matter production when rice plant is subsequently exposed to drought condition. Our over-all result showed that the mutation both affected shoot (number of tillers) and root branching. Nevertheless, several traits between mutant and wild-type were compared by obtaining ratio of traits to number of tillers. Under drought, the mutant slightly increased shoot dry weight that may be attributed to the higher water uptake as a result of maintained root system. Concurrently, glucose and sucrose concentrations in the mutant roots were higher while its starch concentration was lower and glucose/sucrose concentrations were higher in the stem. Candidate causal gene of the mutant is a subunit of Mediator Complex and its possible regulation to sugar-related genes is currently being explored.