Implications of nitrogen metabolism in plant basal resistance and priming

Abstract: Nitrate transporters are membrane proteins in charge of nitrate transport through theroots. Among the nitrate transporters, AtNRT2.1 and AtNRT2.2 are the main transporters involvedin uptake of nitrate when it is present at low concentrations through a high-affinity transportsystem (HATS). Apart from nitrate transport, it is speculated that these transporters, the gene orthe protein, may have additional roles in signaling and definition of root architecture. A mutationin both high affinity nitrate transporters (AtNRT2.1 and AtNRT2.2) confers enhanced resistanceagainst Pseudomonas syringae by priming SA dependent responses. Enhancement of SA markergenes PR-1 and PR-5 is correlated with increases of the hormone SA during the first 48h afterinfection. Interestingly, AtNRT2 induction after three days of nitrate starvation results inenhanced susceptibility in wild-type plants against Pst. In addition, mutant plants showed alteredABA control by Pst. ABA level does not change in atnrt2 during the infection while it isincreased in wild type plants. Coronatine less Pst DC3118 produces reduced symptoms on Wsbackground while it grows as Pst DC3000 in atnrt2.1. Therefore it seems that atnrt2 displayssome interference with ABA signaling, which probably results in a deficient ABA control by thepathogen. All these results suggest that both transporters may act as environmental sensors ofabiotic/biotic stress modifying plant responses to pathogens.