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

## TL;DR

This study identifies and analyzes Hsp70 genes in Hylocereus undatus seedlings under heat stress, finding that HuHsp70-11 is a key gene involved in the plant's heat response.

## Contribution

The study identifies 27 Hsp70 genes in Hylocereus undatus and highlights HuHsp70-11 as a key candidate gene for heat stress response.

## Key findings

- Twenty-seven HuHsp70 genes were identified and classified into five subfamilies with conserved structures and motifs.
- HuHsp70-11 was found to be a key gene whose expression increases with prolonged heat shock.
- A model suggests HuHsp70-11 helps remove reactive oxygen species and improve cell membrane permeability under heat stress.

## Abstract

Hylocereus undatus 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 HuHsp70 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 HuHsp70-11 is a key candidate. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed that HuHsp70s, especially HuHsp70-11, play key roles in responding to high temperatures (HT) in H. undatus seedlings. A potential model by which HuHsp70-11 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 H. undatus plants to heat stress.