Efeito da superexpressão do fator de transcrição OsDof25 sobre a eficiência de absorção de nitrogênio em Orysa sativa L.

Abstract

Nitrogen is one of the nutrient elements most limiting for plant growth. Thus, increasing plant nitrogen usage efficiency (NUE) is an essential factor for sustainable agriculture, leading to an increased food production with less fertilizer input and less environment impact. The aim of this study was to evaluate the effect of OsDof25 overexpression on N-NO3- and N-NH4+ uptake. In transgenic rice plants, OsDof25 was expressed under control of maize ubiquitin promoter (UBIL:OsDof25:3xHA). Two experiments were conducted: one to evaluate the kinetic parameters Vmáx and KM, and another to analyze the expression level of nitrate (NRT2.1~2.2 and NAR) and ammonium transporters (AMT1.1~1.3), both under high and low NO3- and NH4+ supply. The untransformed plants showed higher growth that transformed lineages. The L1 and L2 showed a lower value of the KM in the resupply treatment of 0.2 mM N-NO3-. In the resupply with 0.2 mM N-NH4 + the L4 showed higher Vmax and L1 lower KM. There were no large variations in uptake kinetics between the transformed and untransformed plants. At the root the NRT2 showed low expression in lineages L1 and L4, when under constant supply of N-NO3-, in contrast, in the treatment under resupply with 0.2 mM N-NO3-was increased expression of OsNTR2.1 ~ 2.2, and NAR in both transformed lineages, but in the root the concentration of NO3- was opposed to the expression of NRT2 and NAR, in both conditions. In the leaves, the line L4 showed high expression of the transporter OsNRT2.1 with the resupply of 0.2 and 2.0 mM N-NO3-. In plants grown under constant supply of N-NH4+, L1 showed lower expression of AMT1 in the root compared to L4 and untransformed plants. When subjected to nitrogen deficiency, there was an increased expression of the OsAMT1.2. However, there was no correlation between N transporter expression levels and NO3- and NH4+ content in the transformed plants, indicating a possible change in enzyme activity and reduction or assimilation of N in these plants. The transformed plants when subjected to resupply with low levels of nitrate and ammonium showed better response parameters Vmax and KM compared to the untransformed. In the plants transformed the resupply with nitrate at low concentration resulted in increasing the gene expression of the transporters (OsNTR2.1 ~ 2.2 and protein OsNAR2.1), and the treatment with constant supply provided greatest nitrate accumulation in these plants. The results of both kinetic parameters and accumulation of fresh matter suggest that plants transformed for the expression of the OsDof25 presented highest tolerance to nutritional stress.