Genome-wide identification, expression analysis of the JmjC gene family in tobacco and functional characterization of NtJMJ19 role in nicotine biosynthesis

Proteins containing the JmjC domain are epigenetic regulators that function as histone lysine demethylases. By modulating chromatin structure and accessibility, they play crucial roles as transcriptional regulators in various processes, including plant growth and development, and abiotic stress responses. However, their functions in regulating secondary metabolism remain unclear. In this study, 31 JMJ genes were identified in tobacco, which were located on nine linkage groups and classified into five subfamilies based on phylogenetic relationships. Additionally, segmental duplication was found to be the primary factor driving the expansion of JmjC gene family in tobacco. Transcriptome data revealed that the expression levels of JMJ genes were generally higher in roots than in leaves. Importantly, four genes (NtJMJ6, NtJMJ8, NtJMJ17, and NtJMJ19), belonging to the PKDM8 subfamily, were significantly upregulated in roots following topping. Numerous hormone-responsive, and stress-responsive cis-elements were detected within promoter regions, and NtJMJ19 could be strongly induced by JA. Further studies demonstrated that the transcription levels of these four genes (NtJMJ6, NtJMJ8, NtJMJ17, and NtJMJ19) were markedly increased in high-nicotine germplasms compared to low-nicotine germplasms using RT-qPCR. Analysis of knockout lines confirmed that NtJMJ19 positively regulated both nicotine and JA content. In summary, this study systematically identified the JmjC gene family in tobacco and discovered that the NtJMJ19 was related to nicotine biosynthesis. These findings enhance our understanding of the evolutionary relationship within the tobacco JmjC gene family and provide a foundation for elucidating its functions in secondary metabolism, particularly nicotine biosynthesis.