Fig. 2

Schematic representation of the major pathway of secondary metabolite biosynthesis and its interrelationships with primary metabolites. Primary metabolites are interconnected with secondary metabolism by producing secondary metabolite compounds through the biosynthetic pathway. Types of biosynthetic pathways in plant secondary metabolism are shikimic acid (shikimate), malonic acid (malonate), mevalonic acid (mevalonate), and methylerythritol-phosphate pathways. Plant secondary metabolites (SMs) are mainly divided into three different groups, including terpenes, phenolics and nitrogen-containing compounds, derived from photosynthesis as the primary carbon metabolism process through the four biosynthetic pathways