Fatty Alcohol Oxidase 3 (FAO3) and FAO4b as Mediators Connect the Alcohol- and Alkane-forming Pathways in Arabidopsis Stem Wax.

Alcohol- and alkane-forming pathways in cuticular wax biosynthesis are well characterized in Arabidopsis. However, potential interactions between the two pathways remain unclear. Our study revealed that mutation of CER4, the key gene in the alcohol-forming pathway, also led to a deficiency in alkane-forming pathway in distal stems. To trace the connection between these two pathways, we characterized two homologs of fatty alcohol oxidase (FAO), FAO3 and FAO4b, which were highly expressed in distal stems and localized to the endoplasmic reticulum. The amounts of waxes from the alkane-forming pathway were significantly decreased in stems of fao4b, and much lower in fao3 fao4b, indicative of an overlapping function for both proteins in wax synthesis. Additionally, overexpression of FAO3 and FAO4b in Arabidopsis resulted in a dramatic reduction of primary alcohols and significant increase of aldehydes and related waxes. Moreover, expressing FAO3 or FAO4b led to significantly decreased amounts of C18 - C26 alcohols in yeast co-expressing CER4 and FAR1. Collectively, these findings demonstrate that FAO3 and FAO4b are functionally redundant in suppression of primary alcohols accumulation and contribution to aldehyde production, which provides a missing and long sought-after link between the two pathways in wax biosynthesis.