Genome-wide identification and expression analysis of the HSP70 gene family in Artemisia annua L. under heat stress.

Artemisia annua L., a well-known traditional Chinese medicine, is the main source for production of artemisinin, an anti-malaria drug. Heat shock protein 70 (HSP70) plays an important role in plant growth and development as well as in response to biotic and abiotic stresses. While the HSP70 gene family has been characterized in many species, its role in A. annua remains unclear. To investigate the evolutionary relationships, functions, and expression patterns of the A. annua HSP70 (AaHSP70) gene family, we conducted a comprehensive bioinformatics analysis of the HSP70 gene family in the LQ-9 haplotype 0 genome of A. annua. In this study, 47 AaHSP70 genes containing the HSP70 protein structural domain were identified and were unevenly distributed on seven chromosomes, among which, 39 AaHSP70 genes contained 10 identical conserved motifs and eight genes contained varying numbers of seven to nine motifs. Genome collinearity analysis showed that two pairs of genes were duplicated in genome and duplicated segmental duplication (DSD) was the major mode of amplification for this gene family. Cis-acting elements analysis indicated that AaHSP70 was involved in responding to various biotic and abiotic stresses, such as abscisic acid-responsive and defense and stress responsiveness. Gene expression profiling showed that 45 differentially expressed genes (DEGs) of AaHSP70 genes responded differently to heat treatment, of which 12 genes were up-regulated and two genes were up-regulated and then down-regulated. Gene ontology (GO) enrichment showed that two AaHSP70 genes were enriched in the pathway related to reactive oxygen species (ROS). Furthermore, reverse transcription-qPCR (RT-qPCR) experiments confirmed the expression levels of 10 up-regulated genes. This study provides a comprehensive characterization of the HSP70 gene family in A. annua and systematically identifies AaHSP70 genes that were responsive to heat stress, laying the groundwork for further research into the role of the HSP70 gene family in the response of A. annua to abiotic stress.