The Interaction Between Auxin Signling And Nitrogen Signaling Is Involved In Root Development In Arabidopsis

Root system is very important for the plant absorbing water and mineral nutrients from the soil and supporting the plant. Nitrogen is an essential macronutrient for the plants and plays an important role during plant growth and development.The Arabidopisisis root system is affected by external factors, such as the different concentrations of KNO3. A high concentration of nitrate causes inhibition of lateral root emergence and promote lateral root initiation; a low concentration of nitrate stimulates lateral root enlongtion and promotes lateral root emergence. The present studies suggest that auxin plays an important role on root system of Arabidopisis. According to the results, we speculate that auxin is involved in the regulation of different concentrations of KNO3on the root system. Based on the above observations, we carried out the following experiments:1. Detection of the expression levels of DR5::GFP on primary root and lateral root treated by different concentrations of KNO3. As a result, the expression levels of the DR5::GFP on root tips is higher with a high concentration of nitrate treatment than that in the low concentration of nitrate. Moreover, auxin receptor mutant tirl-1is less sensitive to the KNO3treatment. These results suggest that auxin is involved in KNO3regulated root architecture.2. Screening of arfs involved in KNO3signaling from ARF gene family. We screened out arfn mutant, which is less sensitive to high concentration of KNO3and more sensitive to low KNO3compared to the Col control. We also found that ARFnpro::GFP is down-regulated under high concentration of KNO3and up-regulated under low KNO3. In addition, phenotypice assay of arfn indicated that ARFn can induce lateral root initiation and emergence. These results indicate high concentration of KNO3suppress the lateral root emergence by down-regulating ARFn, which can explain why mutant arfn is less sensitive to high concentration of KNO3.3. Screening of ARFn interactors. We screened out IAA17and IAA27as ARFn interactors by Yeast two-hybrid assays and the interaction between IAA27and ARFn were further verified with Tobacco by bimolecular fluorescence complementation experiment by injecting Tobacco leaf. We found iaa17has more emergent lateral roots and fewer lateral root initiations, which is opposite to arfn which has more lateral root initiations and fewer emergent lateral roots. These phenotypes are in line with the interaction between ARFn and IAA17. Our results provide some clues about how ARFn mediates auxin signaling and regulates lateral root development.