为了解α-淀粉酶在红肉火龙果〔Hylocereus polyrhizus (F. A. C. Weber) Britton et Rose〕果实淀粉降解中的作用，对红肉火龙果α-淀粉酶基因HpAMY3进行克隆和生物信息学分析，检测果实发育期间该酶的活性及其编码基因的表达，同时对HpAMY3重组蛋白的淀粉降解活性进行分析。结果表明：HpAMY3基因的开放阅读框长度为2 742 bp，编码913个氨基酸；HpAMY3蛋白的理论相对分子质量为102 370，理论等电点为pI 6.02，预测此蛋白位于叶绿体，且为亲水性蛋白。系统进化分析表明HpAMY3与拟南芥〔Arabidopsis thaliana (Linn.) Heynh.〕AtAMY3的亲缘关系最近，均属于AMY Ⅲ类。亚细胞定位实验结果显示HpAMY3定位于本氏烟草（Nicotiana benthamiana Domin）叶片的叶绿体，表明HpAMY3具有质体定位的特点。在授粉后20和23 d，红肉火龙果果实的α-淀粉酶活性较低；在授粉后25 d，α-淀粉酶活性显著（P＜0.05）升高；在授粉后27和30 d，α-淀粉酶活性保持在较高水平。红肉火龙果果实的HpAMY3基因相对表达量在授粉后20和23 d较低，在授粉后25和27 d持续升高，在授粉后30 d略有降低。红肉火龙果果实发育期间α-淀粉酶活性与HpAMY3基因相对表达量的相关性较高（R₂=0.94）。体外淀粉降解活性实验结果显示：在含有HpAMY3重组蛋白的反应体系中均检测到麦芽糖和麦芽三糖，且二者含量极显著（P＜0.01）高于含有载体对照pDR196的反应体系。综合上述结果，HpAMY3蛋白可能定位于红肉火龙果果实的淀粉体；在果实发育期间，HpAMY3基因上调表达，HpAMY3具有淀粉降解活性。

 To understand the effect of α-amylase in the starch degradation of Hylocereus polyrhizus (F. A. C. Weber) Britton et Rose fruits, the α-amylase gene HpAMY3 in H. polyrhizus was cloned and the bioinformatics analysis was conducted, the activity of this enzyme and the expression of its encoding gene during fruit development were detected, meawhile, the starch degradation activity of HpAMY3 recombinant protein was analyzed. The results show that the length of the open reading frame. of HpAMY3 gene is 2 742 bp, encoding 913 amino acids; the theoretical relative molecular mass of HpAMY3 protein is 102 370, and its theoretical isoelectric point is pI 6.02; it is predicted that HpAMY3 is located in chloroplast, and it is a hydrophilic protein. The phylogenetic analysis shows that HpAMY3 is most closely related to AtAMY3 in Arabidopsis thaliana (Linn.) Heynh., and both of them belong to AMY Ⅲ class. The subcellular localization experiment result shows that HpAMY3 is localized in chloroplast of Nicotiana benthamiana Domin leaves, indicating that HpAMY3 has the characteristic of plastid localization. At 20 and 23 d of post-pollination, the α-amylase activities in H. polyrhizus fruits are relatively low; at 25 d of post-pollination, the α-amylase activity significantly (P<0.05) increases; at 27 and 30 d of post-pollination, the α-amylase activities maintain at a relatively high level. At 20 and 23 d of post-pollination, the relative expressions of HpAMY3 gene in H. polyrhizus fruits are relatively low; at 25 and 27 d of post-pollination, the relative expressions of HpAMY3 gene continuously increase; at 30 d of post-pollination, the relative expression of HpAMY3 gene slightly decreases. There is a relatively high correlation (R₂=0.94) between the α-amylase activity and the relative expression of HpAMY3 gene during fruit development of H. polyrhizus. The in vitro starch degradation activity experiment result shows that maltose and maltotriose are detected in the reaction system containing the HpAMY3 recombinant protein, and their contents are extremely significantly (P<0.01) higher than those in the reaction system containing the vector control pDR196. It is suggested that the HpAMY3 protein may be localized in the amyloplast of H. polyrhizus fruits; during fruit development, the expression of HpAMY3 gene is up-regulated, and HpAMY3 has starch degradation activity.