**6.3 Modern breeding methods (MBTs)**

The rapid growth and usage of genome editing tools has opened up new ways for introducing change and influencing gene expression at multiple levels, including transcription, mRNA processing, and mRNA translation. CRISPR/Cas9 technology has primarily been used to study plant biosynthetic potential by blocking competing biosynthetic pathways and changing metabolite flux towards target chemical synthesis. One such example, the Salvia miltiorrhiza rosmarinic acid synthase (*SmRAS*) gene was edited using the CRISPR/Cas9 technology [139]. This mutation led to a decrease in phenolic acid content, such asrosmarinic acid, and an increase in its precursor, 3,4-dihydroxyphenyl lactic acid, especially in the homozygous variety. Another study in *S. miltiorrhiza* employed CRISPR/Cas9 to knock out the *SmCPS1* gene, which codes for a diterpene synthase involved in tanshinone synthesis. This was done to investigate the feasibility of encouraging the accumulation of the substrate for taxol synthesis as tanshinones and taxol sharing the same precursor (Geranylgeranyl Pyrophosphate) [140].
