Phytosterols: Structural variations, biosynthetic pathways, and their biological roles

Phytosterols are a diverse class of isoprenoid-derived lipids that serve as essential structural components of plant membranes and regulators of growth and reproduction. Unlike animals and fungi, which predominantly utilize cholesterol and ergosterol, plants produce a complex array of over 250 sterol molecules. These include major forms such as β-sitosterol, stigmasterol, and campesterol as well as minor components like cholesterol and various sterol biosynthetic intermediates. This review provides a comprehensive overview of plant sterols, first addressing their structural diversity and distribution across species and tissues, and then exploring their biosynthesis, transport, and functions. A key focus is placed on their role as membrane modulators, influencing fluidity, permeability, and the formation of lipid rafts. Finally, we synthesize genetic and molecular evidence, demonstrating the critical functions of sterols and their derivatives in both reproductive and vegetative development. We conclude by highlighting persistent gaps in our knowledge and proposing future research directions to unravel the multifaceted roles of these essential molecules.