Plant epidermal wax is a layer of hydrophobic lipids covering the surface of terrestrial plants. It is known that epidermal wax plays an important role in inhibiting non-stomatal dehydration of plants, protecting plants from pests and diseases, preventing ultraviolet radiation, and it is very important for regulating plant growth and development and stress resistance. As the first contact surface with the environment, the composition, content, and crystal structure of the plant epidermal wax are sensitive to changes in various environmental factors (such as light, drought, humidity, etc.), but its internal regulation mechanism is still not clear.  

Researchers from the Wuhan Botanical Garden investigated the underlying mechanism that how the photoperiod affected the epidermal waxy synthesis through various technical methods including biochemistry, molecular biology, and genetics.  

The study demonstrates that the miR156-SPL9 (SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 9) regulatory module plays an important role in plant epidermal wax synthesis. Further research finds that SPL9 promotes waxy synthesis by directly regulating the expression of CER1 (a key enzyme for waxy component alkane synthesis) and indirect regulation of CER4 (a key enzyme for waxy component fatty alcohols synthesis).   

More importantly, this study reveals the important role of miR156-SPL9-DEWAX module in regulating plant wax accumulation in response to photoperiod. The antagonistic effects between SPL9 and DEWAX proteins, as well as their own genes and protein expressions are regulated by light and photoperiods, enabling plants to respond more quickly and flexibly to changes in the surrounding environment.  

This is the first report on the on-off mechanism of plant epidermal wax synthesis. The results will provide a new theoretical basis for the physiological and biochemical activities of plant wax synthesis in response to environmental changes, and will help to reconstruct the wax layer of crops to enhance the ability of crops to resist stress in the context of global changes.  

This work was supported by the National Natural Science Foundation of China. Dr. LI Rongjun (associate professor of the Wuhan Botanical Garden) and Dr.  LI Linmao (now a postdoctoral fellow in the College of Life Sciences of Wuhan University) are co-first authors of the paper. Professor  Lü Shiyou is the corresponding author (now in College of Life Science of the Hubei University). The relevant results have been published on The Plant Cell under the title “Diurnal Regulation of Plant Epidermal Wax Synthesis through Antagonistic Roles of the Transcription Factors SPL9 and DEWAX”.  

Altered wax phenotypes of MIR156 and SPL9-related mutants (Image by LI Rongjun) 

A working model of photoperiod regulated plant epidermal wax synthesis (Image by LI Rongjun)