A comprehensive catalog of single nucleotide polymorphisms (SNPs) from the black pepper (Piper nigrum L.) genome

Single nucleotide polymorphisms (SNPs) have emerged as the marker of choice in breeding and genetics, particularly in non-model organisms such as black pepper (Piper nigrum L.), a globally recognized spice crop. This study presents a comprehensive catalog of SNPs in the black pepper genome using data from 30 samples obtained from RNA sequencing and restriction site-associated DNA sequencing, retrieved from the Sequence Read Archive, and their consequences at the sequence level.

Three SNP calling and filtering pipelines, namely BCFtools, Genome Analysis Toolkit (GATK)-soft filtering, and GATK-hard filtering, were employed. Results revealed 498,128, 396,003, and 312,153 SNPs respectively identified by these pipelines, with 260,026 SNPs commonly detected across all methods. Analysis of SNP distribution across the 45 scaffolds of the black pepper genome showed varying densities, with pseudo-chromosomes Pn25 (0.86 SNPs/kb), Pn8 (0.74 SNPs/kb), and Pn7 (0.72 SNPs/kb) exhibiting the highest densities. Conversely, scaffolds Pn27 to Pn43 exhibited minimal SNP distribution, except Pn45. Approximately 34.80% of SNPs exhibited stronger genetic linkage (r² > 0.7). Moreover, SNPs predominately mapped to downstream (≈ 32.54%), upstream (≈ 22.52%), and exonic (≈ 16.20%) regions of genes. Transition substitution accounted for the majority (≈ 57.42%) of identified SNPs, resulting in an average transition-to-transversion ratio of 1.36. Notably, 56.09% of SNPs were non-synonymous, with a significant proportion (≈ 53.59%) being missense mutations. Additionally, 12,491 SNPs with high or moderate impacts were identified, particularly in genes associated with secondary metabolism and alkaloid biosynthesis pathways. Furthermore, the expression of 675 genes was potentially influenced by local (cis-acting) SNPs, while 554 genes were affected by distal (trans-acting) SNPs.

The findings of the present study underscore the utility of identified SNPs and their targets, especially those impacting important pathways, for future genetic investigations and crop improvement efforts in black pepper. The characterization of SNPs in genes related to secondary metabolism and alkaloid biosynthesis highlights their potential for targeted breeding aimed at enhancing the yield, quality, and resilience of this economically important crop in diverse environmental conditions.