Drought poses a serious challenge to sustained plant growth and crop yields in the context of global climate change. Drought tolerance in poplars and their underlying mechanisms still remain largely unknown. In this article, we investigated the overexpression of PtoMYB99 – both a drought and abscisic acid (ABA) induced gene constraining drought tolerance in poplars (as compared with wild type poplars). First, we found that PtoMYB99-OE lines exhibited increased stomatal opening and conductance, higher transpiration and photosynthetic rates, as well as reduced levels of ABA and jasmonic acid (JA). Second, PtoMYB99-OE lines accumulated more reactive oxygen species (ROS), including H₂O₂ and O₂⁻, as well as malonaldehyde (MDA), proline, and soluble sugar under osmotic stress; conversely, the activity of antioxidant enzymes (SOD, POD, and CAT), was weakened in the PtoMYB99-OE lines. Third, the expression of ABA biosynthetic genes, PtoNCED3.1 and PtoNCED3.2, as well as JA biosynthetic genes, PtoOPR3.1 and PtoOPR3.2, was significantly reduced in the PtoMYB99-OE lines under both normal conditions and osmotic stress. Based on our results, we conclude that the overexpression of PtoMYB99 compromises tolerance to osmotic stress in poplar. These findings contribute to the understanding of the role of the MYB genes in drought stress and the biosynthesis of ABA and JA.

在全球气候变化的背景下，干旱对植物的持续生长和农作物产量构成了严峻的挑战。杨树的耐旱性及其潜在机制仍然很大程度上未知。在本文中，我们研究了 PtoMYB99 的过度表达——干旱和脱落酸 (ABA) 诱导的基因限制了杨树的耐旱性（与野生型杨树相比）。首先，我们发现 PtoMYB99-OE 品系表现出气孔开放度和导度增加、蒸腾作用和光合速率更高，以及 ABA 和茉莉酸 (JA) 水平降低。其次，PtoMYB99-OE 系积累了更多的活性氧 (ROS)，包括 H ₂ O ₂ 和 O ₂ ⁻ ，如以及渗透胁迫下的丙二醛（MDA）、脯氨酸和可溶性糖；相反，PtoMYB99-OE 系中抗氧化酶（SOD、POD 和 CAT）的活性减弱。第三，在正常条件和渗透胁迫下，PtoMYB99-OE系中ABA生物合成基因PtoNCED3.1和PtoNCED3.2以及JA生物合成基因PtoOPR3.1和PtoOPR3.2的表达均显着降低。根据我们的结果，我们得出结论，PtoMYB99 的过度表达会损害杨树对渗透胁迫的耐受性。这些发现有助于理解 MYB 基因在干旱胁迫以及 ABA 和 JA 生物合成中的作用。