PeSHN1 regulates water-use efficiency and drought tolerance by modulating wax biosynthesis in poplar

Wax, a hydrophobic structure that provides an effective waterproof barrier to the leaves, is an important drought adaptation trait for preventing water loss. However, limited knowledge exists regarding the molecular mechanisms underlying wax biosynthesis in trees. Here, PeSHN1, an AP2/ethylene response factor transcription factor, was isolated from a fast-growing poplar Populus × euramericana cv. 'Neva' clone. To study the potential biological functions of PeSHN1, transgenic 84K poplar (Populus alba × Populus glandulosa) plants overexpressing PeSHN1 were generated. PeSHN1 overexpression resulted in decreased transpiration, increased water-use efficiency (WUE) and increased drought tolerance. The transgenic poplar plants exhibited increased wax accumulation and altered wax composition, mainly because of a substantial increase in long-chain (>C30) fatty acids, aldehydes and alkanes. Gene expression analyses revealed that many genes involved in wax biosynthesis were induced in the PeSHN1 overexpression plants. In addition, chromatin immunoprecipitation-PCR assays and dual luciferase assays revealed that at least one of those genes, LACS2, is likely targeted by PeSHN1. Moreover, the PeSHN1 overexpression plants maintained higher photosynthetic activity and accumulated more biomass under drought stress conditions. Taken together, these results suggest that PeSHN1 regulates both WUE and drought tolerance in poplar by modulating wax biosynthesis and that altered PeSHN1 expression could represent a novel approach (altering the wax trait on leaf surfaces to increase WUE) for breeding drought-tolerant plants.