Genome-wide identification and characterization of BAHD acyltransferases in black pepper (Piper nigrum L.) reveals their important role in piperine biosynthesis

Black pepper (Piper nigrum L.) is one of the most popular spices in the world. It derives its popularity from the pleasant aroma of the berries or fruits, which are the economically useful parts of the plant. The principle active ingredient of black pepper is an amide called piperine (1-piperoyl piperidine), which confers the characteristic pungency and taste to the berries. Its biosynthesis involves an enzymatic step of acylation, catalyzed by the enzyme piperine synthase, which is a member of the BAHD superfamily of acyltransferases. This gene family has not been identified and characterized in black pepper, except for a few members. In the present study, we identified and characterized the BAHD-acyltransferases in black pepper through a genome-wide analysis. A total of 110 BAHD-acyltransferases with an average length of 391 amino acids were identified, with the majority possessing the conserved HXXXD and DFGWG motifs. Most genes were intronless. The genes identified to potentially encode for the piperine synthase activity were temporally regulated with higher transcript accumulation at the mid developmental stages of fruits, 30–60 days after anthesis (DAA), compared to the early and late stages. This coincided with the fruit piperine content/accumulation, which was estimated through HPLC (high-performance liquid chromatography), at the same developmental stages. The gene PnBAHD70 was identified and validated to be coding for piperine synthase, with a Log2 fold change of more than 200 (p ≤ 0.05) at DS6 (60 DAA). The gene exhibited a high degree of sequence conservation with its ortholog in P. argyrophyllum and in silico analysis revealed that the protein demonstrated a high interaction potential with one of its possible ligands, acetyl-CoA. The identification of these genes allows us to understand the genetic basis of temporal variation in the piperine content of berries and provides a foundation for the development of black pepper varieties with enhanced piperine content.