Genome-Wide Identification and Expression Analysis of the Hsp70 Gene Family in Hylocereus undatus Seedlings Under Heat Shock Stress

<i>Hylocereus undatus</i> growth is limited by long-term heat stress, and heat shock protein 70 (Hsp70) is crucial in the plant's heat stress (HS) response. In a previous study, transcriptomic data revealed that Hsp70 family members in pitaya seedlings respond to temperature changes. This study identified 27 <i>HuHsp70</i> genes in pitaya, analyzed their physicochemical properties (such as molecular weight and isoelectric point), and divided them into five subfamilies with conserved gene structures, motifs (short conserved sequence patterns), and cis-acting elements (regulatory DNA sequences). The Ks value (synonymous substitution rate) ranged from 0.93~3.54, and gene duplication events occurred between 71.17 and 272.19 million years ago (Mya). Under HS, eight and nine differentially expressed genes (DEGs) were detected at 24 h and 48 h, respectively. Quantitative real-time PCR (qRT-PCR, a method for measuring gene expression) verified the expression trends, with HuHsp70-11 expression increasing with heat shock duration, indicating that <i>HuHsp70-11</i> is a key candidate. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed that <i>HuHsp70s</i>, especially <i>HuHsp70-11</i>, play key roles in responding to high temperatures (HT) in <i>H. undatus</i> seedlings. A potential model by which <i>HuHsp70-11</i> removes excess reactive oxygen species (ROS) and enhances cell membrane permeability was constructed. These results provide new perspectives for exploring the HS response mechanisms and adaptability of <i>H. undatus</i> plants to heat stress.