SPL1 positively regulates cuticular ridge wax biosynthesis in Arabidopsis

• SPL1/SPL12 deficiency disrupts cuticular wax biosynthesis, causing sepal fusion and reduced fertility. • SPL1 transcriptionally activates CER1, CER1L , and CER4 , essential for alkane and alcohol synthesis in sepal cuticular ridges. • HSP70–16 enhances SPL1-mediated activation of wax biosynthesis genes, promoting cuticular ridge formation. The plant cuticle serves as a critical protective barrier against diverse environmental stresses. In various species, cuticles of sepals and petals display distinct ridge-like structures. However, the molecular mechanisms underlying the formation and maintenance of these cuticular ridges have remained enigmatic. Here, we elucidate that the production of cuticular ridge wax is regulated by SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) transcription factors in Arabidopsis. SPL1 and SPL12 double mutants ( spl1spl12 ) exhibit severe defects in cuticular ridge formation, coupled with markedly reduced seed-setting rates and increased organ fusion compared to wild-type plants. Furthermore, we demonstrate that SPL1 positively regulate the expression of key enzymes involved in wax biosynthesis, including the alkane-forming enzymes ECERIFERUM1 (CER1), CER1-like (CER1L), and the primary (1-) alcohol-forming enzyme CER4. These enzymes are essential for the synthesis of alkanes and 1-alcohols, which are vital for the accumulation of cuticular ridge wax. Additionally, we identified that HSP70–16 interacts with SPL1, enhancing its transcriptional activity. Together, these results uncover a regulatory network essential for cuticular ridge formation and provide insights into plant developmental processes. Model for SPL1-mediated wax homeostasis regulation in Arabidopsis sepal. The molecular chaperone complex comprising SPL1, HSP70–16, and its co-chaperone DnaJ orchestrates the transcriptional activation of core enzymatic components (CER1L, CER1, and CER4) in the cuticular wax biosynthesis pathway, specifically regulating alkane and alcohol production. Sufficient accumulation of alkanes and alcohols at the cell surface leads to the formation of natural cuticular ridges, preventing sepal adhesion and abnormal flowering, thus ensuring proper seed setting.