Involved in nicotinate detoxification in planta (PubMed:28533213). Catalyzes the conversion of nicotinate to N-methylnicotinate, which is a detoxified form of endogenous nicotinate in planta (PubMed:28533213). nicotinate + S-adenosyl-L-methionine = N-methylnicotinate + S-adenosyl-L-homocysteine kcat is 3.52 sec(-1) with nicotinate as substrate (PubMed:28533213). kcat is 3.01 sec(-1) with S-adenosyl-L-methionine as substrate (PubMed:28533213). Highly expressed in anthers, pistils, developing siliques, and developing seeds. Belongs to the class I-like SAM-binding methyltransferase superfamily. Cation-independent O-methyltransferase family.