Gap-free genome and efficient transcript purification system reveals the genomes diversity and chlorophyll degradation mechanism in pitaya.

Pitaya is an important perennial herbaceous fruit tree. The color of fruit determines pitaya nutritive (and attractive) value, which is considered as an important objective in breeding improvement. In this study, we reported the first telomere-to-telomere (T2T) gap-free genome of "Shuangse No. 1" pitaya (Hylocereus polyrhizus; red peel). Two high-quality genomes for "Dahong" (H. polyrhizus; red peel) and "Honghuaqinglong" (H. stenopterus; stay-green) were further assembled, aiming to explore the genetic diversity of pitaya genomes. In further analysis, we noticed a high proportion of viral contamination in pitaya tissues, which hindered the efficient utilization of transcriptomic data. To address this issue, we analyzed 111 pitaya transcriptome data from different geographic regions to characterize and separate viral components. Then we developed an efficient, novel, and universal transcript purification system for pitaya transcriptomes by applying it to 27 samples from different tissues and species, thereby enhancing the utility for transcriptomic and broader biological research. Combining the purified transcriptomic data with comparative genomic analyses, we identified HuERF72, a transcription factor (TF) that potentially regulates chlorophyll degradation in pitaya. Interaction assays and plant transformation elucidated that HuERF72 acts as a repressive TF by directly binding to the promoter of HuSGR1, a key structural gene in the chlorophyll degradation pathway. This study provides high-quality genomic resources and novel methodologies for molecular investigations in pitaya. Additionally, the proposed regulatory network advances our understanding of the transcriptional regulatory mechanisms underlying chlorophyll degradation, offering valuable insights into the genetic improvement of pitaya.