The NAC transcription factors (TFs) play important roles in mediating abiotic stress tolerance; however, the mechanism is still not fully known. Here, an NAC gene (BpNAC90) from a gene regulatory network of Betula platyphylla (birch) that responded to drought was characterized. Overexpression and knockout of BpNAC90 displayed increased and reduced drought tolerance, respectively, relative to wild-type (WT) birch. BpNAC90 binds to different DNA motifs to regulate target genes in conferring drought tolerance, such as Eomes2, ABRE and Tgif2. BpNAC90 is phosphorylated by drought stress at Ser 205 by birch SNF1-related protein kinase 2 (BpSRK2A). Mutated BpNAC90 (termed S205A) with abolished phosphorylation, was transformed into birch for overexpression. The transgenic S205A plants displayed significantly reduced drought tolerance compared with plants overexpressing BpNAC90, but still showed increased drought tolerance relative to WT birch. At the same time, S205A showed a decreased capability to bind to motifs and reduced activation of target gene expression, which contributed to the reduced drought tolerance. Additionally, BpSRK2A and BpNAC90 can be induced by drought stress and form a complex to phosphorylate BpNAC90. The results together indicated that phosphorylation of BpNAC90 is necessary in conferring drought tolerance in birch.

中文翻译：

---

桦树 BpNAC90 的磷酸化可提高基因表达的激活，从而赋予其耐旱性

NAC转录因子（TF）在介导非生物胁迫耐受性中发挥重要作用；然而，其机制仍不完全清楚。在这里，对来自白桦（Betula platyphylla）基因调控网络的响应干旱的 NAC 基因（BpNAC90）进行了表征。相对于野生型（WT）桦树，BpNAC90 的过表达和敲除分别表现出耐旱性增强和降低。BpNAC90 与不同的 DNA 基序结合，调节赋予耐旱性的靶基因，例如 Eomes2、ABRE 和 Tgif2。BpNAC90 因干旱胁迫而被桦树 SNF1 相关蛋白激酶 2 (BpSRK2A) 在 Ser 205 处磷酸化。磷酸化被破坏的突变 BpNAC90（称为 S205A）被转化到桦树中进行过度表达。与过表达BpNAC90的植物相比，转基因S205A植物表现出显着降低的耐旱性，但相对于WT桦树仍表现出增加的耐旱性。同时，S205A 显示出与基序结合的能力下降以及靶基因表达的激活减少，这导致耐旱性降低。此外，BpSRK2A 和 BpNAC90 可由干旱胁迫诱导并形成复合物以使 BpNAC90 磷酸化。这些结果共同表明 BpNAC90 的磷酸化对于赋予桦树的耐旱性是必要的。