Contribuição do transportador OsNRT2.4 para a absorção de nitrato e modulação da arquitetura radicular em arroz sob baixa disponibilidade de nitrogênio

Abstract

The availability of nutrients in the soil influences growth modulation and root architecture. Nitrogen (N) is one of the factors that most limits plant growth and productivity, as plants with a nitrogen deficiency invest more in root depth and do not limit lateral elongation of the root system. For efficient nutrient uptake to occur, specific transporters located on the plasma membrane are required to assist in the entry of the nutrient into the cellular interior, with emphasis on high-affinity nitrate transporters (NRT2). Thus, plants silencing the OsNRT2.4 gene, obtained through the gene silencing technique by artificial microRNA (amiRNA), and control plants (WT - wild type) were submitted to a low nitrate dose condition, with the aim of investigating the role of the OsNRT2.4 transporter in the promotion of root growth stimulus. After the process transformation, the seedlings obtained were transferred to greenhouse at the Department of Soils of UFRRJ, to obtain first generation seeds (T1). Seeds of the obtained lines presented problems regarding the germination, so a protocol to break seed dormancy was established to overcome the problem. Subsequently, three experiments were conducted in a growth chamber (fitotron). The first and second experiments were conducted in order to select those lines silencing the OsNRT2.4 gene. The lines and WT plants were grown in nutrient solution under a low nitrate dose (0.2 mM N-NO3 -) and selected based on the analysis of gene expression by the comparative CT method (2-C T) and by the morphology and root parameters analysis, experiments I and II, respectively. Experiment III was carried out with the previously selected lines, L#5 and L#39. The aim was to analyze the effect of the silencing of the OsNRT2.4 gene on the soluble metabolites and on the expression pattern of enzymes of the metabolism of N and the high-affinity nitrate transporters, cultured in nutrient solution under low dose and resupply (0.1 mM N-NO3 -). It was observed that the silencing of the OsNRT2.4 gene induced a WT-like lateral root density, but lower lateral root elongation, smaller surface area, lower volume and fewer tips, confirming that the OsNRT2.4 transporter has a role in the regulation of root growth, being specifically involved in the growth of lateral roots. The silencing also affected the expression of other high-affinity nitrate transporters (OsNRT2.1 e OsNAR2.1). In addition, the OsNRT2.4 transporter has a role in the internal N flux regulation, acting in the nitrate transport from roots to shoot (efflux).