背景回顾：Pitaya (Hylocereus) is the most economically important fleshy-fruited tree of the Cactaceae family that is grown worldwide, and it has attracted significant attention because of its betalain-abundant fruits. 

提出问题：Nonetheless, the lack of a pitaya reference genome significantly hinders studies focused on its evolution, as well as the potential for genetic improvement of this crop. 

主要研究：Herein, we employed various sequencing approaches, namely, PacBio-SMRT, Illumina HiSeq paired-end, 10× Genomics, and Hi-C (high-throughput chromosome conformation capture) to provide a chromosome-level genomic assembly of ‘GHB’ pitaya (H. undatus, 2n = 2x = 22 chromosomes). 

结果1-组装、注释：The size of the assembled pitaya genome was 1.41 Gb, with a scaffold N50 of ~127.15 Mb. In total, 27,753 protein-coding genes and 896.31 Mb of repetitive sequences in the H. undatus genome were annotated. 

结果2-基因组演化之全基因组复制事件：Pitaya has undergone a WGT (whole-genome triplication), and a recent WGD (whole-genome duplication) occurred after the gamma event, which is common to the other species in Cactaceae. 

结果3-基因组演化之重复序列爆发：A total of 29,328 intact LTR-RTs (~696.45 Mb) were obtained in H. undatus, of which two significantly expanded lineages, Ty1/copia and Ty3/gypsy, were the main drivers of the expanded genome. 

结果4-遗传图谱：A high-density genetic map of F1 hybrid populations of ‘GHB’ × ‘Dahong’ pitayas (H. monacanthus) and their parents were constructed, and a total of 20,872 bin markers were identified (56,380 SNPs) for 11 linkage groups. 

结果5-甜菜素：More importantly, through transcriptomic and WGCNA (weighted gene coexpression network analysis), a global view of the gene regulatory network, including structural genes and the transcription factors involved in pitaya fruit betalain biosynthesis, was presented. 

结论：Our data present a valuable resource for facilitating molecular breeding programs of pitaya and shed novel light on its genomic evolution, as well as the modulation of betalain biosynthesis in edible fruits.

 摘 要 

火龙果（量天尺属）是仙人掌科中最具经济价值的肉质果树，在全球广泛种植，因其果实富含甜菜素而备受关注。然而，目前仍然缺乏火龙果的参考基因组，严重阻碍了对该果树的演化研究，以及该作物的遗传改良潜力。本文中，作者结合PacBio三代、Illumina二代、10× Genomics以及Hi-C数据，组装了量天尺‘GHB’（Hylocereus undatus，2n = 2x = 22）的基因组。组装的火龙果基因组大小为1.41 Gb，scaffold N50约127.15 Mb。作者共注释了27753个蛋白质编码基因，896.31Mb的重复序列。火龙果经历了一次WGT（全基因组三倍化）和一次发生在gamma事件之后的WGD（全基因组复制），这是仙人掌科其他物种所共有的。作者共获得了29328个完整的LTR-RTs，其中两个显著扩张的支系，即Ty1/copia和Ty3/gypsy，是火龙果基因组扩张的主要驱动力。作者基于‘GHB’ × ‘Dahong’的F1杂种群体，构建了一个高密度遗传图谱， 并且分别构建了两个亲本的遗传图谱，在11个连锁群上鉴定了20872个bin标记，包含56380个SNPs。更重要的是，通过转录组学和WGCNA分析，作者对火龙果甜菜素生物合成的基因调控网络进行了鉴定，包括结构基因和转录因子。本研究为火龙果的分子育种提供了珍贵的遗传资源，为火龙果的基因组演化及食用果实中甜菜素生物合成的调控提供了新的视野。