Degradome, small RNAs and transcriptome sequencing of a high-nicotine cultivated tobacco uncovers miRNA's function in nicotine biosynthesis.

Tobacco (Nicotiana tabacum) is considered as the model plant for alkaloid research, of which nicotine accounts for 90%. Many nicotine biosynthetic genes have been identified and were known to be regulated by jasmonate-responsive transcription factors. As an important regulator in plant physiological processes, whether small RNAs are involved in nicotine biosynthesis is largely unknown. Here, we combine transcriptome, small RNAs and degradome analysis of two native tobacco germplasms YJ1 and ZY100 to investigate small RNA's function. YJ1 leaves accumulate twofold higher nicotine than ZY100. Transcriptome analysis revealed 3,865 genes which were differently expressed in leaf and root of two germplasms, including some known nicotine and jasmonate pathway genes. By small RNA sequencing, 193 miRNAs were identified to be differentially expressed between YJ1 and ZY100. Using in silico and degradome sequencing approaches, six nicotine biosynthetic genes and seven jasmonate pathway genes were predicted to be targeted by 77 miRNA loci. Three pairs among them were validated by transient expression in vivo. Combined analysis of degradome and transcriptome datasets revealed 51 novel miRNA-mRNA interactions that may regulate nicotine biosynthesis. The comprehensive analysis of our study may provide new insights into the regulatory network of nicotine biosynthesis.