Abstract:Nitrogen is one of the most important nutrients for plant growth, and one of key factors in limiting plant biomass and economic yield. Plants have evolved diverse and complex transport systems to facilitate uptake and reallocation of nitrogen compounds. Except uptake of inorganic nitrogen such as nitrate and ammonium by their specific transporters, plants can also uptake organic nitrogen including amino acids, small peptides and proteins by their corresponding transporters as nitrogen source. In higher plants, there are two types of nitrate transporters, known as low affinity nitrate transporter family (NRT1) and high affinity nitrate transporter family (NRT2). On the other hand, two families of small-peptide transporters have been recognized in eukaryotes, which are the oligopeptide transporter family (OPT) and the peptide transporter family (PTR). OPTs can transport tetra- and pentapeptides, while PTRs can transport di- and tripeptides. Interestingly, PTR family is similarity to NTR1 family based on their protein sequence, and their members usually mixed together to cluster into a homologous group called NTR1/PTR family. This article briefly reviewed on the research progress of nitrate transporter family and small-peptide transporter family in their substrates and physiological roles in plants.
