Anthocyanins are natural pigments with antioxidant effects that exist in various fruits and vegetables. The accumulation of anthocyanins is induced by environmental signals and regulated by transcription factors in plants. Numerous evidence has indicated that among the environmental factors, light is one of the most signal regulatory factors involved in the anthocyanin biosynthesis pathway. However, the signal transduction of light and molecular regulation of anthocyanin synthesis remains to be explored. Here, we focus on the research progress of signal transduction factors for positive and negative regulation in light-dependent and light-independent anthocyanin biosynthesis. In particular, we will discuss light-induced regulatory pathways and related specific regulators of anthocyanin biosynthesis in plants. In addition, an integrated regulatory network of anthocyanin biosynthesis controlled by transcription factors is discussed based on the significant progress.

MicroRNAs (miRNAs) belong to non-coding small RNAs which have been shown to take a regulatory function at the posttranscriptional level in plant growth development and response to abiotic stress. Hemerocallis fulva is an herbaceous perennial plant with fleshy roots, wide distribution, and strong adaptability. However, salt stress is one of the most serious abiotic stresses to limit the growth and production of Hemerocallis fulva. To identify the miRNAs and their targets involved in the salt stress resistance, the salt-tolerant H. fulva with and without NaCl treatment were used as materials, and the expression differences of miRNAs–mRNAs related to salt-tolerance were explored and the cleavage sites between miRNAs and targets were also identified by using degradome sequencing technology. In this study, twenty and three significantly differential expression miRNAs (p-value < 0.05) were identified in the roots and leaves of H. fulva separately. Additionally, 12,691 and 1538 differentially expressed genes (DEGs) were also obtained, respectively, in roots and leaves. Moreover, 222 target genes of 61 family miRNAs were validated by degradome sequencing. Among the DE miRNAs, 29 pairs of miRNA targets displayed negatively correlated expression profiles. The qRT-PCR results also showed that the trends of miRNA and DEG expression were consistent with those of RNA-seq. A gene ontology (GO) enrichment analysis of these targets revealed that the calcium ion pathway, oxidative defense response, microtubule cytoskeleton organization, and DNA binding transcription factor responded to NaCl stress. Five miRNAs, miR156, miR160, miR393, miR166, and miR396, and several hub genes, squamosa promoter-binding-like protein (SPL), auxin response factor 12 (ARF), transport inhibitor response 1-like protein (TIR1), calmodulin-like proteins (CML), and growth-regulating factor 4 (GRF4), might play central roles in the regulation of NaCl-responsive genes. These results indicate that non-coding small RNAs and their target genes that are related to phytohormone signaling, Ca²⁺ signaling, and oxidative defense signaling pathways are involved in H. fulva’s response to NaCl stress.

Proanthocyanidins (PAs), anthocyanins, and flavonols are key flavonoids that play diverse roles in plant physiology and human health. Despite originating from a shared biosynthetic pathway, the regulatory mechanisms of PA biosynthesis and the cooperative regulation of different kinds of flavonoids remain elusive, particularly in flower tissues or organs. Here, we elucidated the regulatory network governing PA biosynthesis in Freesia hybrida ‘Red River®’ by characterizing four TT2-type MYB transcription factors, designated FhMYBPAs. Phylogenetic analysis, subcellular localization, and transactivation assays predicted their roles as PA-related activators. Pearson correlation analysis revealed significant correlations between FhMYBPAs and PA accumulation in various floral tissues and development stages. Functional studies demonstrated that FhMYBPAs activated PA biosynthesis by directly binding to the promoters of target genes, which can be enhanced by FhTT8L. Additionally, a hierarchical and feedback regulatory model involving FhTTG1, FhMYB27, and FhMYBx was proposed for PA biosynthesis. Furthermore, comparative analysis of flavonoid-related MYB factors involving FhPAP1, FhMYB5, FhMYBF1, and FhMYB21L2 highlighted their roles in regulating PA, anthocyanin, and flavonol biosynthesis, with some exhibiting versatile regulations. Overall, our findings provide insights into the spatio-temporal regulation of flavonoids in flowers and expand our understanding of MYB-mediated transcriptional regulation of specialized metabolites in plants.