Overexpression of AtbZIP69 in transgenic wheat confers tolerance to nitrogen and drought stress.

Main conclusion: AtbZIP69 overexpression in wheat significantly enhanced drought and low nitrogen tolerance by modulating ABA synthesis, antioxidant activity, nitrogen allocation, and transporter gene expression, boosting yield. In this study, we generated wheat plants with improved low nitrogen (LN) and drought tolerance by introducing AtbZIP69, a gene encoding a basic leucine zipper domain transcription factor, into the wheat cultivar Shi 4056. AtbZIP69 localized to the nucleus and activated transcription. A greenhouse study further revealed that, compared to wild type (WT) wheat, AtbZIP69 transgenic wheat exhibited significantly increased drought and LN stress tolerance. Under drought stress, the H₂O₂ concentration in transgenic lines decreased, whereas SOD activity and proline content increased, resulting in remarkably enhanced drought resistance. Furthermore, drought stress boosted the expression of critical abscisic acid (ABA) synthesis enzymes as well as the ABA content of transgenic plants, implying that this gene may improve wheat's drought resistance by promoting ABA production. Additionally, during a two-year field test, the yield and the number of spikes of transgenic wheat were significantly higher than those of WT wheat under LN conditions. Mechanistically, the overexpression of AtbZIP69 altered nitrogen distribution by allocating more nitrogen to grains under LN conditions. In addition, the expression of genes encoding nitrogen transporter proteins was higher in AtbZIP69 transgenic wheat than in WT wheat under LN conditions. These findings suggest that the insertion of AtbZIP69 opens up new opportunities for wheat stress resistance breeding.