1. Introduction
Medicinal plants have been used for thousands of years as traditional remedies worldwide. The bioactive compounds of these plants have proven beneficial for treating human diseases and promoting health. Endemic medicinal plants found only in certain geographic regions often have unique properties that have evolved in their isolated habitats. Iran, located at the intersection of Central Asia, West Asia, and the Middle East, harbors more than 8,000 plant species, approximately 1,900 of which are endemic [
1]. Many of these endemic species have a long history of use in traditional Iranian medicine for treating conditions such as infections, inflammation, pain, and digestive issues [
2]. As rich sources of specialized metabolites and bioactive compounds, Iran's endemic medicinal flora represent an immense repository of plant chemical diversity waiting to be explored for new drug leads and treatment possibilities. Understanding these endemic plants through genomic, phytochemical and pharmacological studies can provide insights for developing improved therapies and advancing human health [
3].
Apiaceae, also known as Umbelliferae, is an economically important family of flowering plants consisting of more than 3,700 species, including crops, herbs, spices, and medicinal plants. Major Apiaceae crops include carrots, celery, parsley, parsnip, and fennel, which are cultivated worldwide for their edible taproots, stems, leaves, or seeds that add flavor, nutrients and medicinal value to human diets [
4]. Many Apiaceae species contain bioactive compounds and essential oils that give them antimicrobial, insecticidal, and pharmaceutical properties. Popular medicinal Apiaceae plants include anise, caraway, cumin, coriander, dill, and asafetida and are used extensively in traditional medicine systems and herbal remedies globally. The Apiaceae family has a worldwide distribution but is most abundant in temperate climates. Several genera, such as Ferula, Prangos and Kelussia, predominantly occur around the Mediterranean and across West and Central Asia [
5,
6]. Understanding the phytochemical diversity of Apiaceae species through genomic and metabolomic studies can aid in selective breeding efforts and expand the utilization of medicinal members within this vital plant family for improved food security and enhanced medication use [
6,
7].
The genus Ferula belongs to the economically significant Apiaceae family and comprises more than 170 species of flowering plants. Most members of this genus are perennial herbaceous plants that grow in arid grasslands and mountains ranging from Central Asia to northern Africa [
8]. The characteristic features of Ferula species include thick roots, sturdy hollow stems, and feathery leaves, and they produce resins and gums that contain bioactive compounds such as terpenoids, coumarins, and alkaloids [
9]. These specialized metabolites confer antispasmodic, antimicrobial, and anti-inflammatory effects to Ferula plants, underlying their extensive use in traditional medicine systems in Iran and neighboring countries [
9,
10].
Ferula pseudalliacea is an indigenous medicinal plant species endemic to the Zagros mountainous regions of Iran's Kurdistan Province and western border areas. This species has been traditionally utilized in folk medicine for various purposes, including as an antiparasitic and antiulcer remedy [
11]. Several new bioactive sesquiterpene coumarins, including kamonolol acetate, farnesiferol B, sanandajin, ethyl galbanate, methyl galbanate, and fekrynol acetate, have been isolated and identified from
F. pseudalliacea [
12]. These compounds have exhibited potent anticancer, antiplasmodial, antibacterial and strong antioxidant effects, revealing the medicinal potential of these endemic species [
13,
14]. However, despite harboring such valuable specialized metabolites,
F. pseudalliacea has a narrow geographical range with scattered fragmented populations, leading to its classification as a threatened plant [
15]. With rich phytochemical diversity and proven pharmacological properties, further conservation efforts and molecular research on
F. pseudalliacea can facilitate sustainable utilization of this medicinal species as well as the discovery of novel bioactive lead compounds.
Cinnamate 4-hydroxylase (C4H) is a cytochrome P450-dependent monooxygenase that catalyzes a key step in phenylpropanoid metabolism across plant species. It controls the conversion of trans-cinnamic acid to p-coumaric acid, funneling metabolites toward myriad phenolic end products such as lignins, coumarins, flavonoids, anthocyanins, and stilbenoids [
16,
17]. These phenolic compounds act as structural barriers or chemical defenses in plants while also exerting beneficial antioxidant, anti-inflammatory, and antimicrobial effects. C4H belongs to the CYP73A enzyme family and is encoded by a multigene family whose members are induced differentially by biotic and abiotic stresses [
18]. Complete genomic sequences and individual
C4H gene functions have already been well characterized in model crop species using molecular genetics tools [
19]. Structural modeling revealed conserved heme-binding and substrate recognition sites across C4H orthologs from diverse taxa [
20]. However,
C4H has been cloned and sequenced in several medicinal plant species, such as
Salvia miltiorrhiza [
21],
Scrophularia striata [
22],
Euphorbia maculata [
23], and
Carthamus tinctorius [
24]; its sequence has not been explored among key medicinal species, such as Ferula, which are rich reservoirs of phenylpropanoid-derived chemicals. Elucidating
C4H genes in such plants can reveal their evolutionary relationships and regulatory patterns governing species-specific phenolic secondary metabolism. Overall, advances in C4H research have allowed improved metabolic engineering strategies for enhancing the biosynthesis of high-value phenolics in medicinal and crop plants. Currently, little information exists regarding the sequence and expression patterns of
C4H in industrially and conservationally important Ferula species, particularly
F. pseudalliacea. Hence, the current study aimed to i) isolate and sequence the
C4H gene from
F. pseudalliacea using 3’-RACE methods; ii) conduct bioinformatic analysis of the obtained C4H sequences, including conserved domains, evolutionary relationships, and predicted structural features; and iii) quantify the expression profiles of individual
C4H genes across roots, stems, leaves, flowers and seeds of
F. pseudalliacea plants via real-time PCR.
4. Discussion
C4H is involved in the biosynthesis of phenylpropanoids, which are important active plant compounds that participate in the production of valuable secondary metabolites. There is not enough information on the
C4H gene as a key gene in the biosynthesis of several secondary metabolites in the Ferula genus. In this study, the isolation and identification of this gene and its expression level in different organs of
Ferula pseudalliacea plants were carried out. The results revealed that
F. pseudaliacea has one isoform of the
C4H gene (
FpC4H). Only one member of this gene has been identified in
Arabidopsis [
39], parsley [
39], cowpea [
40] and black raspberry [
41]. However, in sycamore [
42], subabel tree [
43] and rapeseed [
44], C4H is encoded by a small gene family. For instance, four
C4H genes were found in the soybean genome [
20] and
Populus kitakamiensis genome [
45]. The number of copies of a gene can be related to polyploidy events and segmental and tandem duplications [
46,
47]. Increasing the number of isoforms of a gene can be effective at increasing functional diversity and related interactions [
48]. Phylogenetic analysis of C4H proteins revealed that there is a large genetic distance between the
C4H genes of monocot and dicot plants, suggesting that they have undergone a different evolutionary process. Most likely, after the derivation of dicotyledons and monocotyledons, structural diversity occurred in the
C4H genes. Despite this genetic difference, C4Hs have similar physicochemical characteristics, revealing that the conditions and environment of activity are the same. A region (consisting of eleven amino acids) was identified in the conserved region of C4H proteins, which showed high variation between orthologs. This region could be involved in the functional diversity of orthologs, although further molecular studies on this region are needed.
An investigation of the FpC4H protein structure revealed that there is an extensive binding region in this protein. The presence of many binding regions in a protein can affect its extent of activity and interaction. Additionally, the amino acids isoleucine and leucine likely play more prominent roles in the binding and interaction of FpC4H. In addition, two ion binding regions, cysteine 258 and asparagine 217, were recognized in the FpC4H structure. The common feature of CYP450 family members is the presence of an iron core in their protein structure, which is connected to a cysteine amino acid [
49]. Additionally, four serine residues were identified as potential phosphorylation sites in the FpC4H protein. Phosphorylation is a posttranslational modification that affects the activity and life of a protein [
50]. For proteins such as C4H, which is an upstream element in metabolite synthesis pathways, phosphorylation plays a critical role in controlling downstream components by influencing these proteins. The results of the interaction network confirmed that FpC4H interacts with proteins involved in the biosynthesis of secondary metabolites. For example, biological process terms, including phenylpropanoid metabolic/biosynthetic process, polyketide biosynthetic process, flavonoid biosynthetic process, aromatic amino acid family catabolic process, and cinnamic acid biosynthetic process, were significantly enriched in FpC4H (
Figure 6c). Phenylpropanoids and flavonoids play key roles in the response to adverse conditions, including abiotic and biotic stresses [
51], as well as in plant growth processes [
52]. Previous studies have shown that the expression of the
C4H gene in the leaves of
Lepidium apetalum after methyl jasmonate treatment is correlated with the flavonoid biosynthesis pathway [
53]. Additionally, the flavonoid content at different stages in the tea plant
Camellia sinensis was correlated with the expression pattern of
C4Hb [
54]. In addition, downregulation of the
C4H gene in
Nicotiana tabacum via the use of CRISPRi could increase flavonoid biosynthesis [
55]. According to these results, it is hypothesized that the
C4H gene is an important element in the biosynthesis of secondary metabolites and that this gene affects the improvement of plant resistance to adverse environmental conditions.
The
FpC4H gene exhibited diverse expression levels in different organs, including the roots, stems, leaves, flowers, and seeds of
F. pseudallicea, and the expression of this gene was detected in all organs (
Figure 7). The results revealed that
FpC4H is expressed in a tissue-specific manner. For example, the
FpC4H gene was more strongly induced in floral tissues than in other tissues. In contrast, the
C4H-2 gene was more highly expressed in rapeseed seeds than in roots and flowers [
44]. Moreover, diverse expression levels were observed between four
C4H genes in the soybean genome [
20]. Metabolomics analysis of different organs of
F. pseudallicea revealed that phenolic compounds accumulated more in flowers than in other organs [
11]. The high expression level of the
FpC4H gene in reproductive organs such as flowers suggested that this gene is positively correlated with the production of phenolic compounds, which can be considered in metabolite engineering studies.