The Function of <i>PpKCS6</i> in Regulating Cuticular Wax Synthesis and Drought Resistance of Kentucky Bluegrass

Drought stress significantly limits plant growth and crop productivity. Cuticular wax minimizes plant water loss and contributes to drought resistance. Kentucky bluegrass (Poa pratensis L.) is a widely used cool-season turfgrass worldwide. However, the molecular mechanisms underlying the regulation of dynamic changes in cuticular wax in relation to drought resistance in Kentucky bluegrass remain unclear. Here, we compared molecular mechanisms of cuticular wax biosynthesis in two Kentucky bluegrass cultivars 'Maoershan' (drought-tolerant) and 'Brilliant' (drought-sensitive). The results showed that 'Brilliant' with lower wax content, suffered more severe morphological and physiological damage from drought stress than the 'Maoershan'. Through transcriptome analysis of these two cultivars, a hub gene of PpKCS6, involved in cuticular wax synthesis, was identified. Overexpression of PpKCS6 promoted the synthesis of very long-chain fatty acids, especially increased the content of fatty acids and alkanes with carbon chains above C24. This led to greater cuticular wax accumulation, which further protected the plants against water loss and improved photosynthesis and water use efficiency. Alternatively, RNAi-PpKCS6 lines exhibited the opposite performance to the overexpression line. These results demonstrate that PpKCS6 plays an important role in drought stress resistance by regulating wax biosynthesis.