PagAPX9, an ascorbate peroxidase gene from poplar, promotes growth and enhances drought tolerance in Populus

Drought is widely regarded as a significant abiotic stress restricting the growth of plants via oxidative stress. The ascorbate peroxidase (APX) protein serves a pivotal function in the antioxidant system. However, the function of PagAPX9, a homologue of Arabidopsis thaliana APX1 (AtAPX1), in poplar growth and drought responses remains unclear.

In this study, the PagAPX9 gene, which was induced by drought stress and specifically expressed in young leaves and stems, was cloned successfully from the hybrid poplar '84K' (Populus alba × Populus glandulosa) and used to generate PagAPX9 overexpression transgenic poplars (PagAPX9 OE). The morphological characteristics were evaluated and the physiological indicators explored to determine the mechanism by which PagAPX9 OE plants enhance their drought tolerance.

We found that the PagAPX9 OE lines exhibited promoted high growth and enhanced drought tolerance, with better growth performance and fewer wilting symptoms. Physiological analyses showed that PagAPX9 OE had stronger stomatal regulation and higher efficiency in water use, along with enhanced activities of antioxidant enzymes (superoxide dismutase, peroxidase and catalase) and upregulated expression of antioxidant-related genes. These responses collectively contributed to the maintenance of cellular homeostasis and improved detoxification of reactive oxygen species under water deficit.

Our results showed that PagAPX9 enhanced poplar drought resistance by regulating stomatal behaviour and the scavenging of reactive oxygen species and identified it as a valuable genetic resource to enhance woody plant drought resilience.