Mutants lacking wild-type MLO (Mildew resistance Locus O) proteins show broad-spectrum resistance to the powdery mildew fungus, and dysregulated cell death control, with spontaneous cell death in response to developmental or abiotic stimuli. In order to understand the evolution and divergence patterns of the MLO gene family in Rosaceae plants, we analysed systematically genome-wide data from Fragaria vesca, Prunus persica, Prunus mume, Malus domestica, Pyrus bretschneideri and Rubus occidentalis based on bioinformatics methods. Using three phylogenetic methods (the neighbour-joining, maximum likelihood, and Bayesian methods), we identified 117 MLO genes from 6 Rosaceae species. The results of all three phylogenetic analysis methods supported that these genes were divided into six clades. Conserved motif analysis found that only motif 2 was present in all MLO proteins and had 3 nearly invariant amino acid residues. The findings indicated that motif 2 might be shared by the MLO gene family. The structural features of these genes showed large variations in sequence length among different species, although the lengths and the numbers of exons exhibited high degrees of similarity. Selective pressure analysis showed extremely significant differences in all 6 clades, with 2, 1, and 1 site(s) under significant positive selection detected in clades III, IV, and VI, respectively. These positive selection sites were important driving forces for the promotion of the functional differentiation of the MLO genes. Functional divergence analysis showed that the significantly divergent sites were located within the domains of the MLO genes. Functional distance analysis showed that the clade V had more conservative functions and might have retained more original functions during the evolutionary process. However, clade I may have undergone extensive altered functional constraints as a specialised functional role. Moreover, the most original function of the MLO genes in Rosaceae could be related to the evolution of their resistance to powdery mildew, which then gradually evolved into functions such as the regulation of flower development, the control of root morphology, and seed evolution due to the different evolutionary rates after gene duplication. These results provide a theoretical basis for further studies of the molecular evolutionary patterns of the plant MLO gene family.

缺乏野生型 MLO（抗霉病基因座 O）蛋白的突变体显示出对白粉病真菌的广谱抗性和失调的细胞死亡控制，随着发育或非生物刺激而发生自发性细胞死亡。为了了解蔷薇科植物中MLO基因家族的进化和分化模式，我们基于生物信息学方法系统地分析了来自草莓、桃李、李属、苹果、梨属和西葫芦的全基因组数据。使用三种系统发育方法（邻接法、最大似然法和贝叶斯方法），我们确定了 117 个MLO来自 6 个蔷薇科物种的基因。所有三种系统发育分析方法的结果都支持这些基因分为六个进化枝。保守基序分析发现所有 MLO 蛋白中仅存在基序 2，并且具有 3 个几乎不变的氨基酸残基。调查结果表明，MLO可能共享motif 2基因家族。尽管外显子的长度和数量表现出高度的相似性，但这些基因的结构特征在不同物种之间显示出很大的序列长度差异。选择性压力分析显示，所有 6 个进化枝中都存在极其显着的差异，分别在进化枝 III、IV 和 VI 中检测到显着正选择下的 2、1 和 1 个位点。这些正选择位点是促进MLO基因功能分化的重要驱动力。功能差异分析表明，显着差异站点位于MLO域内基因。功能距离分析表明，进化枝V具有更保守的功能，可能在进化过程中保留了更多的原始功能。然而，进化枝 I 作为一个专门的功能角色，可能已经经历了广泛改变的功能限制。此外，蔷薇科MLO基因最原始的功能可能与其抗白粉病的进化有关，然后逐渐进化为调控花发育、控制根系形态和种子进化等功能。基因复制后不同的进化速率。这些结果为进一步研究植物MLO基因家族的分子进化模式提供了理论依据。