Emerging Insights Into Cuticular Wax Biosynthesis and Its Response to Abiotic Stresses

Cuticular waxes, together with cutin, form a hydrophobic barrier that protects the plants against various biotic and abiotic stresses. The past decade has seen remarkable progress in deciphering the wax biosynthesis and transport, however, the continuous discovery of wax-defective mutants and the development of diverse technologies are progressively refining our current understanding of wax biosynthetic pathways. Here, we provide a comprehensive summary of the biosynthetic pathway and transport mechanisms of plant cuticular waxes, with a particular emphasis on recent breakthroughs, including the carbon reallocation mechanism between the alkane-forming and alcohol-forming pathways, as well as the emerging branched-chain wax biosynthesis pathway. We also review how wax synthesis responds to diverse abiotic stresses, including salt, extreme water conditions and temperature, light, and outline critical knowledge gaps that remain to be addressed, including the wax biosynthesis in non-model plants, the physiological function of branched wax and their underlying molecular mechanisms.