Cholesterol/analogs & derivatives; Erythritol/analogs & derivatives; Mevalonic Acid/metabolism; Nicotiana/enzymology; Phytosterols/metabolism; Sugar Phosphates/metabolism; Withania/enzymology; Withanolides/metabolism; Base Sequence; Biosynthetic Pathways; Carbon/metabolism; Cholesterol/chemistry; Cholesterol/metabolism; Erythritol/metabolism; Gene Expression; Gene Expression Regulation, Plant; Mevalonic Acid/chemistry; Molecular Sequence Data; Phylogeny; Phytosterols/chemistry; Plant Leaves/chemistry; Plant Leaves/enzymology; Plant Leaves/genetics; Plant Proteins/genetics; Plant Proteins/metabolism; Plants, Genetically Modified; Sequence Analysis, DNA; Sitosterols/chemistry; Sitosterols/metabolism; Sterols/chemistry; Sterols/metabolism; Stigmasterol/chemistry; Stigmasterol/metabolism; Nicotiana/genetics; Triterpenes/chemistry; Triterpenes/metabolism; Withania/chemistry; Withania/genetics; Withanolides/chemistry