# Lavandula Species, Their Bioactive Phytochemicals, and Their Biosynthetic Regulation
## 5 Biosynthesis Regulation of Lavelender Bioactive Phytochemicals
### The Role of Transcription Factors and microRNAs in the Biosynthesis of Secondary Metabolites  
Gene regulation provided by transcription factors (TFs) is crucial for ensuring that the correct genes are activated or repressed at the appropriate time and place, thereby allowing cells to respond to different stimuli and perform diverse functions. Study which examined TFs that regulate the expression of key genes involved in monoterepenoid biosynthesis in _L. \(\times\) intermedia_ indicated that the _LINS_ and _CINS_ genes are regulated by TFs that possess conserved domains that are typical of MYB, bZIP, NAC, GeBP, and SBP-related proteins [103]. The results of the study indicate that the _LINS_ and _CINS_ genes are regulated by TFs that possess conserved domains that are typical of MYB, bZIP, NAC, GeBP, and SBP-related proteins. Structural genes, and also TFs themselves, can be regulated by small noncoding RNA molecules--miRNAs.MiRNAs regulate gene expression by binding to complementary sequences in messenger RNA, leading to the degradation or repression of translation. A considerable amount of literature has been published on the regulatory role that miRNAs play in the biosynthesis of secondary metabolites [104; 105; 106]. Computational analysis of miRNA molecules involved in secondary metabolism in _Menthu_ spp. revealed 11 miRNA families, which targeted 130 transcripts involved in various metabolic processes. The biosynthesis of terpenoids is inferred to be regulated by miR156, miR414, and miR5021, while trichome development is associated with miR156, miR5021, and miR5015b. Out of all identified miRNAs, miR5021 regulated the largest number of transcripts involved in the secondary metabolism of _Menthu_ spp. [104]. In other model plants, it was also reported that miR5021 is involved in terpenoid backbone biosynthesis by targeting _HMGR_, isopentyl diphosphate isomerase (_IDI_), hydroxymethyljuphosphate synthase (_HDS_), geranylgeranyl diphosphate synthase (_GGDPS_), diphosphomevalonate decarboxylase (_MVD_) [107; 108; 109], and transcription factors belonging to MYB family, which, among other things, were proven to be involved in the regulation of sesquiterpene and diterpene biosynthesis [110; 111; 107]. In _Ocimum basilicum_ L., miR5021 may also play an important role in cysteine and methionine metabolism [112]. The regulation role of miR156 on terpenoid biosynthesis is likely to be mediated by the squamous promoter binding protein-like (SPL) transcription factor. It has been reported that miR156 targets the SPL transcription factor in both _A. thaliana_ (L.) [PERSON] and patchouli (_Pogostemon cablin_ Benth), which is also a member of the _Lamiaceae_ family. By binding to its promoters, SPL activates genes of sesquiterpene synthases (_TPS21_ in _A. thaliana_ and PTS in patchouli), thus increasing the production of sesquiterpenenes [113]. Analysis of small RNA (sRNA) libraries obtained via tissue-specific sequencing of _Salvia miltiorrhiza_ Bunge revealed 452 known miRNAs and 40 novel miRNAs, all of which could be classified into 62 miRNA families. Tissue-specific expression patterns were observed for numerous miRNAs identified in this study. Using a degradome sequencing approach, followed by gene ontology (GO) and KEGG pathway analysis, it was discovered that miR5072 cleaves acetyl-CoA C-acetyltransferase, which is involved in the biosynthesis of terpenoids [114]. Another study identified 19 potential target genes for 18 miRNAs predicted from the ETS library of _Salvia sclarea_ L. In addition to miR156 regulating SPL expression, miR828 was found to target MYB family transcription factors, while AP2 domain-containing transcription factors mRNAs were targeted by miR172 [115]. AP2 domain-containing transcription factors were first linked to terpenoid metabolism in _Catharantthus roseus_ (L.) [PERSON]. [116]. Significant downregulation in sesquiterpenoid and triterpenoid biosynthesis pathways was observed in _S.