Catalytic subunit of the NatB N-alpha-acetyltransferase complex. Involved in plant immunity through the regulation of SNC1 stability (PubMed:25966763). acetyl-CoA + N-terminal L-methionyl-L-asparaginyl-[protein] = CoA + H(+) + N-terminal N(alpha)-acetyl-L-methionyl-L-asparaginyl-[protein] acetyl-CoA + N-terminal L-methionyl-L-glutaminyl-[protein] = CoA + H(+) + N-terminal N(alpha)-acetyl-L-methionyl-L-glutaminyl-[protein] acetyl-CoA + N-terminal L-methionyl-L-aspartyl-[protein] = CoA + H(+) + N-terminal N(alpha)-acetyl-L-methionyl-L-aspartyl-[protein] acetyl-CoA + N-terminal L-methionyl-L-glutamyl-[protein] = CoA + H(+) + N-terminal N(alpha)-acetyl-L-methionyl-L-glutamyl-[protein] Reticulated leaves, early flowering and aborted or unfertilized ovules in siliques. Belongs to the acetyltransferase family. ARD1 subfamily.