The F-box Protein SAGL1 and ECERIFERUM3 Regulate Cuticular Wax Biosynthesis in Response to Changes in Humidity in Arabidopsis.

Cuticular waxes that cover the above-ground parts of land plants are essential for their survival in terrestrial environment. However, little is known about the regulatory mechanisms underlying cuticular wax biosynthesis in response to changes in ambient humidity. Here, we report that SMALL AND GLOSSY LEAVES 1 (SAGL1) Kelch repeat F-box protein mediates proteasome-dependent degradation of ECERIFERUM3 (CER3), a biosynthetic enzyme that is involved in the production of very long chain alkanes, which are the major wax components and thereby negatively regulates cuticular wax biosynthesis in Arabidopsis. Disruption of SAGL1 caused severe growth retardation, enhanced tolerance to drought and increased wax accumulation in stems, leaves, and roots. Cytoplasmic SAGL1 physically interacts with CER3 and targets CER3 for degradation. GUS expression was observed in roots of pSAGL1::GUS plants, but barely detected in their aerial organs. High humidity-induced levels of GUS activity and SAGL1 transcripts were reduced by ABA treatment and water-deficit. SAGL1 protein levels also increased under high humidity and its stability is regulated by the 26S proteasome. This study revealed that the SAGL1-CER3 module negatively regulates Arabidopsis cuticular wax biosynthesis in response to changes to humidity conditions and suggested the importance of permeable cuticle formation in terrestrial plants under high humidity.