Transcriptome-wide identification of the Hsp70 gene family in Pugionium cornutum and functional analysis of PcHsp70-5 under drought stress.

Main conclusion: The PcHsp70-5 enhances drought stress tolerance in transgenic Arabidopsis thaliana by upregulating stress tolerance genes and antioxidant enzyme activities. Heat shock proteins (HSPs) constitute a class of evolutionarily conserved proteins synthesized by organisms in response to various adverse environmental stimuli such as elevated temperatures, drought, hormonal fluctuations, high salt concentrations, and mechanical stress. However, research on HSPs has predominantly focused on model plants and crops, whereas their functions in desert plants have not been well investigated. This study analyzed the transcriptome of Pugionium cornutum and identified the complete ORFs of 25 genes of the PcHsp70 family genes. Their expression levels under drought stress were investigated using existing RNA-seq data. PcHsp70-5 genes exhibited high expression levels in both roots and leaves under drought stress. Consequently, the PcHsp70-5 genes were cloned and transformed into Arabidopsis thaliana for further analysis of their roles in drought stress response. Real-time fluorescence quantitative PCR (qRT-PCR) analysis demonstrated that both, drought stress and ABA, induced PcHsp70-5 expression. Under drought conditions, transgenic Arabidopsis plants exhibited markedly enhanced growth compared to wild-type plants, as evidenced by improved survival rates, root length, fresh weight, chlorophyll content, and reduced levels of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) in leaves, indicating that PcHsp70-5 overexpression mitigated growth inhibition and oxidative damage induced by drought stress. Subsequent research revealed that PcHsp70-5 overexpression significantly augmented the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and increased the proline content in transgenic Arabidopsis under drought conditions, alongside a significant increase in the expression levels of genes related to stress tolerance. This suggests that PcHsp70-5 enhances drought stress tolerance in transgenic Arabidopsis by upregulating stress tolerance genes and antioxidant enzyme activities.