BnA1.CER4 and BnC1.CER4 are redundantly involved in branched primary alcohols in the cuticle wax of Brassica napus

The mutations BnA1.CER4 and BnC1.CER4 produce disordered wax crystals types and alter the composition of epidermal wax, causing increased cuticular permeability and sclerotium resistance. The aerial surfaces of land plants are coated with a cuticle, comprised of cutin and wax, which is a hydrophobic barrier for preventing uncontrolled water loss and environmental damage. However, the mechanisms by which cuticle components are formed are still unknown in Brassica napus L. and were therefore assessed here. BnA1.CER4 and BnC1.CER4, encoding fatty acyl-coenzyme A reductases localizing to the endoplasmic reticulum and highly expressed in leaves, were identified and functionally characterized. Expression of BnA1.CER4 and BnC1.CER4 cDNA in yeast (Saccharomyces cerevisiae) induced the accumulation of primary alcohols with chain lengths of 26 carbons. The mutant line Nilla glossy2 exhibited reduced wax crystal types, and wax composition analysis showed that the levels of branched primary alcohols were decreased, whereas those of the other branched components were increased. Further analysis showed that the mutant had reduced water retention but enhanced resistance to Sclerotinia sclerotiorum. Collectively, our study reports that BnA1.CER4 and BnC1.CER4 are fatty acyl-coenzyme A reductase genes in B. napus with a preference for branched substrates that participate in the biosynthesis of anteiso-primary alcohols.