The Heat Stress Transcription Factor LlHsfA4 Enhanced Basic Thermotolerance through Regulating ROS Metabolism in Lilies (Lilium Longiflorum)

Abstract

Heat stress severely affects the annual agricultural production. Heat stress transcription factors (HSFs) represent a critical regulatory juncture in the heat stress response (HSR) of plants. The HsfA1-dependent pathway has been explored well, but the regulatory mechanism of the HsfA1-independent pathway is still under-investigated. In the present research, HsfA4, an important gene of the HsfA1-independent pathway, was isolated from lilies (<i>Lilium longiflorum</i>) using the RACE method, which encodes 435 amino acids. LlHsfA4 contains a typical domain of HSFs and belongs to the HSF A4 family, according to homology comparisons and phylogenetic analysis. <i>LlHsfA4</i> was mainly expressed in leaves and was induced by heat stress and H₂O₂ using qRT-PCR and GUS staining in transgenic <i>Arabidopsis</i>. LlHsfA4 had transactivation activity and was located in the nucleus and cytoplasm through a yeast one hybrid system and through transient expression in lily protoplasts. Over expressing <i>LlHsfA4</i> in <i>Arabidopsis</i> enhanced its basic thermotolerance, but acquired thermotolerance was not achieved. Further research found that heat stress could increase H₂O₂ content in lily leaves and reduced H₂O₂ accumulation in transgenic plants, which was consistent with the up-regulation of HSR downstream genes such as <i>Heat stress proteins</i> (<i>HSPs</i>), Galactinol synthase1 (<i>GolS1</i>), <i>WRKY DNA binding protein 30</i> (<i>WRKY30</i>), <i>Zinc finger of <i>Arabidopsis</i> thaliana 6</i> (<i>ZAT6</i>) and the ROS-scavenging enzyme <i>Ascorbate peroxidase 2</i> (<i>APX2</i>). In conclusion, these results indicate that LlHsfA4 plays important roles in heat stress response through regulating the ROS metabolism in lilies.