NAD biosynthesis, including from aspartate via the de novo pathway and from nicotinate (NA) via the Preiss-Handler pathway, is conserved in land plants. Meanwhile, different NA conjugates, which are mainly involved in NA detoxification, have been found in all tested land plants. Among these conjugates, MeNA (NA methyl ester) has been widely detected in angiosperm plants, although the physiological function of this compound and the underlying mechanism for its production in planta remain largely unknown. Here, we show that MeNA is an NAD precursor that undergoes more efficient long-distance transport between organs than NA and NAM. We further show that Arabidopsis has one methyltransferase (encoded by At5g04370.1, designated AtNaMT1) that is capable of carboxyl methylation of NA to yield MeNA and one main methyl esterase (MES2, encoded by At2g23600) that is capable of hydrolyzing MeNA back to NA. Additionally, the transfer ratio of [¹⁴C]-MeNA from root to leaf was significantly increased in both MES2 knockdown and NaMT1-overexpressing lines, suggesting that both NaMT1 and MES2 fine-tune the long-distance transport of MeNA, which is ultimately utilized for NAD production. Abiotic stress treatments (salt, ABA, mannitol), which are known to exacerbate NAD degradation, induce NaMT1 expression and specifically suppress MES2 expression. The possible ecological functions of plant MeNA are also discussed.