## 4 Discussion  
In this study, the results showed that the following genes are responsible for the phenylpropanol biosynthetic pathway: _PAL_, _C4H_, _4 CL_, _CHS_, _CHI_, _TAT_, _HPPR_, and _RAS_. These genes were expressed very clearly in the transformed hairy root lines compared to the control within two weeks of light exposure. Previously, several plant species maize _LC_ genes have been used to manipulate the anthocyanin and flavonoid biosynthetic pathways. The introduction of the _LC_ gene might work individually or co-ordinately with C1 to increase flavonoid biosynthesis by triggering flavonoid biosynthetic pathway genes [29]. In dicot plants such as _N. tabacum_ and _A. thaliana_, expression of the _LC_ gene leads to enhanced accumulation of anthocyanin pigmentation [41]. In another study, in petunia, the overexpression of _ZmLC_ genes leads to a higher accumulation of flavonoid content by triggering the flavonoid biosynthetic pathway genes such as _anthocyanidin synthase_, _dihydroflavonol 4-reductase (DFR)_, _flavonol 3'5' hydroxylase (F3'5'H)_, _flavonol 3'-hydroxylase (F3'H)_, and _UDP-glucoseflavonol-3-O-glucosyltransferase_. In addition, it was found that there is a slight increase in the _CHI_, _CHS_, and _flavanone 3-hydroxylase_ gene expression, whereas the _flavonol synthase (FLS)_, _PAL_, _C4H_, _rhammosyltransferase_, and _UDP-rhammose: anthocyanin 3-glucoside_ were not influenced by the _LC_ overexpression [31]. Similar results were obtained in tobacco where overexpression of _LC_ leads to activation of _CHS_ and _DFR_ gene expression [42]. Moreover, exogenous expression of the _LC_ gene in _S. baicalensis_ hairy root leads to increased expression of most of the flavonoid biosynthetic pathway genes [29]. In contrast, in chrysanthemum pigmentation, the expression of _LC_ does not have a noticeable effect. Similarly, in plants such as _Pelargonium_ and _Lisianthus_, ectopic expression of the _ZmLC_ gene does not trigger the _CHI_, _CHS_, _FLS_, and _F3'5'H_ genes [30]. However, in our study, we found that all the phenylpropanolid pathway genes were slightly overexpressed in the _LC_ overexpressed transgenic lines, which leads to a higher accumulation of individual phenolic content, TPC, and TFC. From these results, it is shown that the effect of _ZmLC_ overexpression on flavonoid and phenylpropanolid compounds might be dependent on the species of the plant. In medicinal plants, the phenylpropanol biosynthetic pathways genes such as _PAL_, _C4H_, and _4 CL_ play an important role in rosmarinic acid production. In _Salvia milliorrhiza_, _PAL_ is a main enzyme in the rosmarinic acid biosynthetic pathway, which indicates that alteration in the rosmarinic acid content is directly proportional to the _PAL_ expression [43]. Another study reported that in _S. miliorrhiza_, decreased expression of _PAL_ has an impact on the _C4H_ and _4 CL_ expression [44]. Similarly, in _Melissa officinalis_, it has been reported that the _PAL_ and _4 CL_ expressions are associated with their corresponding enzymatic activities and with the rosmarinic acid content [45]. [PERSON] et al. [1] reported that in _A. rugosa_, the highest expression of _PAL_, _C4H_, and _4 CL_ genes leads to a significant accumulation of rosmarinic acid content. These results were consistent with this study's result that the expression of _PAL_, _C4H_, and _4 CL_ genes was significantly high in the _LC_ overexpressed transgenic lines, which leads to a significant accumulation of rosmarinic acid content. From this result, it is shown that _PAL_, _C4H_, and _CL_ genes are the most important genes responsible for the rosmarinic acid content in most of the plant species. The hypocotyl elongation transcription factor (HY5) and two major photosensizers, phytochrome (PHY)B and cryptochrome (CRY)2, are involved in light-dependent phenylpropanol accumulation in _Arabidopsis_ roots, and many phenylpropanolid genes are highly expressed [46].