Identification and characterization of the TmSnRK2 family proteins related to chicoric acid biosynthesis in Taraxacum mongolicum.

Background: Taraxacum mongolicum is rich in phenolic acids and is widely utilized in food and medicine globally. Our previous research demonstrated that the abscisic acid (ABA) hormone significantly enhances chicoric acid accumulation in T. mongolicum. SNF1-related protein kinase 2s (SnRK2s) are extensively involved in ABA signaling and have the potential to regulate the biosynthesis of phenolic acids.

Results: In this study, liquid chromatography-mass spectrometry (LC-MS) and transcriptomic analyses revealed that the TmbZIP1-Tm4CL1 pathway plays a crucial role in the transcriptional regulation of chicoric acid biosynthesis. Seven TmSnRK2s were identified in T. mongolicum and classified into three groups. Analysis of the TmSnRK2s promoters (2000 bp in length) indicated that the three most prevalent stress-related elements were ABA, methyl jasmonate (MeJA), and light. ABA treatments (0 h, 2 h, 4 h, 8 h, and 24 h) showed that all seven TmSnRK2s were significantly modulated by ABA, with the exception of SnRK2.7. TmSnRK2.2, TmSnRK2.3, TmSnRK2.6, and TmSnRK2.7 were localized in both the cytoplasm and nucleus, whereas TmSnRK2.1 and TmSnRK2.5 were exclusively observed in the cytoplasm. Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays indicated that TmSnRK2.1, TmSnRK2.3, TmSnRK2.6, and TmSnRK2.7 interact with TmbZIP1. The motifs 'Q(S/G)(V/D)(D/E)(I/L)××I(I/V)×EA' and 'D×(D/ED××D)' are identified as the core sites that facilitate the binding of TmSnRK2s to TmbZIP1. Dual-luciferase reporter assays demonstrated that TmSnRK2.3 and TmSnRK2.6 enhance the stability of TmbZIP1 binding to proTm4CL1.

Conclusion: These findings enhance our understanding of the specific roles of certain members of the TmSnRK2 family in the biosynthesis pathway of chicoric acid.