The miRNA838-KCS2 module is involved in the fine regulation of Arabidopsis wax biosynthesis under water-deficient conditions

In terrestrial plants, the outer epidermal surfaces are enveloped by a hydrophobic cuticle, which acts as the primary defense barrier against both abiotic and biotic stresses. While cuticular wax biosynthesis is tightly controlled to protect plants from environmental challenges, its underlying microRNA-mediated regulatory mechanisms remain poorly characterized. Here, we report the function of microRNA838 (miR838) in the fine regulation of cuticular wax biosynthesis in Arabidopsis via controlling the expression of 3-ketoacyl-CoA synthase2 (KCS2), a gene contributing to very-long-chain fatty acids (VLCFAs) biosynthesis during drought stress. Bioinformatic analysis predicted KCS2 as a target of miR838. Expression of both miR838 and KCS2 was higher in roots than in young seedlings, leaves, and stems and significantly induced in Arabidopsis seedlings by dehydration. Coexpression of miR838 and KCS2 or mutated KCS2 (mKCS2), where the miR838-target sequences of KCS2 are mutated, in tobacco leaves revealed that miR838 specifically degraded KCS2 transcripts, but not mKCS2. Transgenic Arabidopsis lines ectopic-expressing artificial miR838 (amiR838) exhibited reduced levels of KCS2 transcripts and decreased total wax loads, particularly reduction in the levels of alkanes and aldehydes, accompanied by downregulation of KCS2 under water-deficient conditions. These findings provide the regulatory role of miR838-KCS2 module and insights into the miRNA-mediated regulation of Arabidopsis cuticular wax biosynthesis in response to water-deficiency.