Pinellia ternata HD-Zip6 gene positively regulates heat stress tolerance in transgenic Arabidopsis by increasing ROS scavenging and NAC019 expression

• PtHDZ6 from Pinellia ternata is highly induced in roots and petioles under heat stress and improves heat tolerance in Arabidopsis . • Overexpression of PtHDZ6 enhances leaf opening, greening rate, root growth, and antioxidant enzyme activities, reducing ROS levels under heat stress conditions. • PtHDZ6 affects genes related to transport, structure, transduction, and antioxidation in transcriptome analyses. • It directly binds and activates the NAC019 promoter, crucial for heat stress response. Pinellia ternata , a vital component of Chinese herbal medicine, encounters "sprout tumble" under high-temperature conditions, leading to diminished yield and quality. However, the mechanisms underlying its response to elevated temperatures remain unclear. Growing evidence indicates that homeodomain-leucine zipper (HD-Zip) transcription factors are crucial in regulating abiotic stress response. However, to date, no HD-Zip proteins have been identified in P. ternata . Herein, we identified and characterized a heat-stimulated HD-Zip I gene, named PtHDZ6 , from P. ternata , which was primarily expressed in roots and petioles and significantly induced by heat stress. Further experiments indicated that PtHDZ6 protein was located within the nucleus and lacked transcriptional activities in yeast. A dual-luciferase assay confirmed that PtHDZ6 is specifically bound to L1 box element. When PtHDZ6 was heterologously expressed in Arabidopsis , it enhanced heat tolerance, as transgenic plants displayed improved leaf opening and greening rate, and root length in response to heat stress. Moreover, under heat stress conditions, these plants displayed reduced accumulation of reactive oxygen species (ROS) and showed increased activities of catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD) in comparison with wild-type plants. Transcriptome analysis demonstrated that overexpression of PtHDZ6 markedly altered the expression of genes associated with transporter function, structural activity, molecular transduction, regulatory roles in molecular functions, and antioxidant processes. Furthermore, PtHDZ6 was found to interact directly with the NAC019 promoter, leading to its upregulation and modulating heat stress responses in Arabidopsis . Collectively, our findings suggest that PtHDZ6 functions as a transcriptional regulator, promoting heat tolerance in plants.