The csi-miR1134-CsMYB16 module regulates drought tolerance via cuticular wax biosynthesis in citrus

Cuticular wax plays crucial roles in plant growth and various environmental stresses. Previous studies on cuticular wax biosynthesis have been reported in many plants. However, the molecular mechanisms of wax biosynthesis at the post-transcriptional level are less studied. Following the observation that csi-miR1134 was upregulated in the pericarp of wax-deficient navel orange fruit, transgenic overexpressing of csi-miR1134 significantly reduced leaf cuticular wax, whereas silencing csi-miR1134 promoted wax biosynthesis and enhanced drought tolerance in citrus. Furthermore, R2R3-MYB transcription factor CsMYB16 was identified as a target of csi-miR1134 and positively regulated cuticular wax biosynthesis and drought tolerance. CsMYB16 was further verified to directly bind to the promoter of the aldehyde decarbonylase-encoding gene ECERIFERUM1 (CsCER1) and activate its expression. Finally, we revealed that the csi-miR1134-CsMYB16-CsCER1 module alters drought tolerance in citrus via cuticular wax biosynthesis. This study reveals a novel post-transcriptional regulatory framework for cuticular wax biosynthesis, thereby providing a theoretical basis for breeding new citrus varieties with enhanced drought tolerance.