Ascorbate peroxidase (APX) is one of the important antioxidant enzymes in the active oxygen metabolism pathway of plants and animals, especially it is the key enzyme to clear H₂O₂ in chloroplast and the main enzyme of vitamin C metabolism. However, knowledge about APX gene family members and their evolutionary and functional characteristics in kiwifruit is limited. In this study, we identified 13 members of the APX gene family in the kiwifruit (cultivar: Hongyang) genome according the APX proteins conserved domain of Arabidopsis thaliana. Phylogenetic analysis by maximum likelihood split these 13 genes into four groups. The APX gene family members were distributed on nine chromosomes (Nos. 4, 5, 11, 13, 20, 21, 23, 25, 28). Most of the encoded hydrophilic and lipid-soluble enzymes were predicted to be located in the cytoplasm, nucleus and chloroplast. Among them, AcAPX4, AcAPX5, AcAPX8, AcAPX12 were transmembrane proteins, and AcAPX8 and AcAPX12 had the same transmembrane domain. The gene structure analysis showed that AcAPXs were composed of 4-22 introns, except that AcAPX10 was intron-free. Multiple expectation maximization for motif elicitation program (MEME) analyzed 13 APX protein sequences of Actinidia chinensis and identified 10 conserved motifs ranging in length from 15 to 50 amino acid residues. Additionally, the predicted secondary structures of the main motifs consisted of α-helix and random coils. The gene expression of fruits in different growth stages and bagging treatment were determined by qRT-PCR. The results showed that 8 AcAPXs had the highest expression levels during the color turning period and only the gene expression of AcAPX3 was consistent with the ascorbic acid content; five AcAPXs were consistent with the ascorbic acid content after bagging. Our data provided evolutionary and functional information of AcAPX gene family members and revealed the gene expression of different members in different growth stages and bagging treatments These results may be useful for future studies of the structures and functions of AcAPX family members.

抗坏血酸过氧化物酶（APX）是动植物体内活性氧代谢途径中重要的抗氧化酶之一，尤其是清除叶绿体中H ₂ O ₂的关键酶和维生素C代谢的主要酶。但是，有关APX基因家族成员及其在猕猴桃中的进化和功能特性的知识是有限的。在这项研究中，我们根据拟南芥APX蛋白的保守结构域确定了猕猴桃（品种：红阳）基因组中APX基因家族的13个成员。通过最大可能性的系统发育分析将这13个基因分为四类。在APX基因家族成员分布在九个染色体上（第4、5、11、13、13、20、21、23、25、28号）。预计大多数编码的亲水和脂溶性酶位于细胞质，细胞核和叶绿体中。其中，AcAPX4，AcAPX5，AcAPX8，AcAPX12是跨膜蛋白，AcAPX8和AcAPX12具有相同的跨膜结构域。基因结构分析表明，AcAPXs由4-22个内含子组成，但AcAPX10无内含子。最大化期望的母题引发程序（MEME）分析了中华猕猴桃的13个APX蛋白序列并鉴定了10个保守的基序，长度从15至50个氨基酸残基不等。另外，主要基序的预测二级结构由α-螺旋和随机线圈组成。通过qRT-PCR确定不同生育阶段和套袋处理的果实的基因表达。结果表明：8种AcAPX在变色期间表达水平最高，只有AcAPX3的基因表达与抗坏血酸含量一致。套袋后五种AcAPX与抗坏血酸含量一致。我们的数据提供了AcAPX的进化和功能信息基因家族成员，并揭示了不同成员在不同生长阶段和装袋处理中的基因表达。这些结果可能对将来对AcAPX家族成员的结构和功能的研究有用。