Cuticular Wax Biosynthesis is Up-Regulated by the MYB94 Transcription Factor in Arabidopsis

The aerial parts of all land plants are covered with hydrophobic cuticular wax layers that act as the first barrier against the environment. The MYB94 transcription factor gene is expressed in abundance in aerial organs and shows a higher expression in the stem epidermis than within the stem. When seedlings were subjected to various treatments, the expression of the MYB94 transcription factor gene was observed to increase approximately 9-fold under drought, 8-fold for ABA treatment and 4-fold for separate NaCl and mannitol treatments. MYB94 harbors the transcriptional activation domain at its C-terminus, and fluorescent signals from MYB94: enhanced yellow fluorescent protein (eYFP) were observed in the nucleus of tobacco epidermis and in transgenic Arabidopsis roots. The total wax loads increased by approximately 2-fold in the leaves of the MYB94-over-expressing (MYB94 OX) lines, as compared with those of the wild type (WT). MYB94 activates the expression of WSD1, KCS2/DAISY, CER2, FAR3 and ECR genes by binding directly to their gene promoters. An increase in the accumulation of cuticular wax was observed to reduce the rate of cuticular transpiration in the leaves of MYB94 OX lines, under drought stress conditions. Taken together, a R2R3-type MYB94 transcription factor activates Arabidopsis cuticular wax biosynthesis and might be important in plant response to environmental stress, including drought.