Drought severely limits plant development and growth; accordingly, plants have evolved strategies to prevent water loss and adapt to water deficit conditions. However, experimental cases that corroborate these evolutionary processes are limited. The LACCASEs (LACs) family is involved in various plant development and growth processes. Here, we performed an evolutionary analysis of LACs from Populus euphratica and characterized the functions of LACs in Arabidopsis and poplar. The results showed that in PeuLACs, multiple gene duplications led to apparent functional redundancy as the result of various selective pressures. Among them, PeuLAC2 underwent strong positive selection. Heterologous expression analyses showed that the overexpression of PeuLAC2 alters the xylem structure of plants, including thickening the secondary cell wall (SCW) and increasing the fiber cell length and stem tensile strength. Altogether, these changes improve the water transport capacity of plants. The analysis of the physiological experimental results showed that PeuLAC2-OE lines exhibited a stronger antioxidant response and greater drought tolerance than WT. Three genes screened by transcriptome analysis, NAC025, BG1, and UGT, that are associated with SCW synthesis and drought stress were all upregulated in the PeuLAC2-OE lines, implying that the overexpression of PeuLAC2 thickened the SCW, improved the water transport capacity of the plant, and further enhanced its drought tolerance. Our study highlights that genes that have undergone adaptive evolution may participate in the development of adaptive traits in P. euphratica and that PeuLAC2 could be a candidate gene for molecular genetic breeding in trees.

中文翻译：

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胡杨中经过适应性进化的基因 LAC2 (LACCASE) 通过提高输水能力来提高耐旱性

干旱严重限制了植物的发育和生长；因此，植物已经进化出防止水分流失和适应缺水条件的策略。然而，证实这些进化过程的实验案例是有限的。漆酶 (LAC) 家族参与各种植物发育和生长过程。在这里，我们进行了进化分析LAC从胡杨并描述了以下功能LAC在拟南芥和杨树。结果表明，在PeuLAC，由于各种选择压力，多个基因重复导致明显的功能冗余。他们之中，PeuLAC2经历了强正选择。异源表达分析表明，PeuLAC2改变植物的木质部结构，包括增厚次生细胞壁（SCW）和增加纤维细胞长度和茎的抗拉强度。总之，这些变化提高了植物的输水能力。生理实验结果分析表明，PeuLAC2-OE系表现出比WT更强的抗氧化反应和更高的耐旱性。通过转录组分析筛选出的三个基因，NAC025,BG1， 和UGT，与 SCW 合成和干旱胁迫相关的在PeuLAC2-OE 线，暗示过度表达PeuLAC2加厚了SCW，提高了植物的输水能力，进一步增强了其抗旱能力。我们的研究强调，经历过适应性进化的基因可能参与了适应性特征的发展。胡杨然后PeuLAC2可能是树木分子遗传育种的候选基因。