Molecular characterization of the Lotus japonicus NRT1(PTR) and NRT2 families

Abstract

Nitrate is an essential element for plant growth, both as a primary nutrient in the nitrogen assimilation pathway and as an important signal for plant development. Low‐ and high‐affinity transport systems are involved in the nitrate uptake from the soil and its distribution between different plant tissues. By an in silico search, we identified putative members of both systems in the model legume Lotus japonicus. We investigated, by a time course analysis, the transcripts abundance in root tissues of nine and four genes encoding putative low‐affinity (NRT1) and high‐affinity (NRT2) nitrate transporters, respectively. The genes were sub‐classified as inducible, repressible and constitutive on the basis of their responses to provision of nitrate, auxin or cytokinin. Furthermore, the analysis of the pattern of expression in root and nodule tissues after Mesorhizobium loti inoculation permitted the identification of sequences significantly regulated during the symbiotic interaction. The interpretation of the global regulative networks obtained allowed to postulate roles for nitrate transporters as possible actors in the cross‐talks between different signalling pathways triggered by biotic and abiotic factors.

Nitrate transporters: an overview in legumes

“…In addition, co-expression of MtNRT2.1 and MtNAR2 suggests interaction of these two proteins for nitrate uptake (Pellizzaro et al 2015). In L. japonicus, two of the four NRT2 genes, LjNRT2.1 and CM0161.180, showed a major increase of transcript abundance in the roots of plants grown under low nitrate concentrations (Criscuolo et al 2012), suggesting involvement of both putative nitrate transporters in the HATS activity.…”

“…Except for this result, our knowledge comes from studies on two model legumes, Lotus japonicus and Medicago truncatula. A molecular characterization of the NPF family in L. japonicus led to the identification of 37 putative LjNPF sequences (Criscuolo et al 2012). Up to now, no gene encoding an NPF has been isolated from L. japonicus.…”

“…Subsequently, two studies were published describing the identification and molecular characterizations of the NRT2 gene family; one using L. japonicus, the other M. truncatula (Criscuolo et al 2012;Pellizzaro et al 2015). In L. japonicus, interrogation of the genome database led to the identification of four putative LjNRT2 named LjNRT2.1, LjNRT2.2, CM0001.20 and CM0161.180 (Criscuolo et al 2012).…”

“…Subsequently, two studies were published describing the identification and molecular characterizations of the NRT2 gene family; one using L. japonicus, the other M. truncatula (Criscuolo et al 2012;Pellizzaro et al 2015). In L. japonicus, interrogation of the genome database led to the identification of four putative LjNRT2 named LjNRT2.1, LjNRT2.2, CM0001.20 and CM0161.180 (Criscuolo et al 2012). Using similar approaches, Pellizzaro et al (2015) revealed, for M. truncatula, a small NRT2 gene family composed of three MtNRT2 genes (named MtNRT2.1, MtNRT2.2 and MtNRT2.3), indicating a similar NRT2 family size in legume or non-legume species.…”

“…Among the nine LjNPF genes studied in L. japonicus, expression of only CM0608.1210 was induced by nitrate. However, without biochemical information and genetic characterizations, the authors were not able to define the functional role in LATS (Criscuolo et al 2012). In M. truncatula, both MtNPFs studied were expressed and characterized in Xenopus oocytes.…”