Comparative transcriptome profiling of fruit tissue provides novel insights into piperine biosynthesis in black pepper (Piper nigrum L.)

Abstract

Black pepper (Piper nigrum L.) is a storehouse of numerous bioactive compounds, most important being the alkaloid piperine. This metabolite has immense applications in both food and pharmaceutical industries. Therefore, studying the pathways involved in piperine biosynthesis is of paramount importance for improving the piperine content in black pepper. In the present study, we have estimated the piperine content across different fruit/berry developmental stages (DS1 to DS8) and leaf tissue of two different traditional landraces of black pepper, using the high-performance liquid chromatography (HPLC) method. Based on the results obtained, the landrace Thottumuriyan was identified to possess higher piperine content amongst the two landraces with high piperine content detected at the mid-developmental stages. The fruit tissues spanning the different developmental stages (DS2, DS4, DS6 and DS8) were selected for comparative transcriptome profiling. An average of 150 million read pairs were generated for the five different samples (4 berry development stages and the leaf tissue). These were mapped against the black pepper reference genome and differentially expressed genes (DEGs) were identified for the four different combinations. Further transcript profiling of twenty candidate genes potentially involved in secondary metabolite biosynthesis pathways, including piperine synthesis, was performed using Real time PCR in the eight different berry developmental stages. Highest expression for the genes associated with piperine biosynthesis was observed at mid-developmental stages. This included the genes coding for piperine synthase and piperic acid-CoA ligase. Our data provides critical information to understand the molecular mechanisms underlying piperine biosynthesis and other pathways in black pepper.