The alternative splicing of ZmHsf23 regulates heat stress tolerance in maize

Heat stress is one of the major threats to maize (Zea mays) production globally. Heat shock transcription factors (HSFs) play vital roles in plant heat stress responses. However, the molecular and genetic basis of HSFs in maize thermotolerance remain largely unknown. In this study, we reveal that the alternative splicing of Hsf23 in maize modulates heat stress tolerance. Hsf23 produces two functional transcripts, the full-length transcript Hsf23b and the heat-inducible transcript Hsf23a. The two Hsf23 transcripts differ by the presence of a cryptic mini exon in Hsf23a, which is spliced out in Hsf23b. Both Hsf23a and Hsf23b were intensely expressed in response to heat stress. The overexpression of Hsf23b, not Hsf23a, enhanced heat stress tolerance, while loss-of-function mutations of Hsf23a and Hsf23b exhibited remarkably increased sensitivity to heat stress. Transcriptome analysis revealed that Hsf23b activates broader heat-responsive genes than Hsf23a, and Hsf23a and Hsf23b modulate heat stress response through different downstream targets. Furthermore, Hsf23a physically interacted with Hsf23b and promotes Hsf23b-regulated expression of sHSP genes. Together, our finding provides new insights into the roles of ZmHsf23 in the heat tolerance in maize, and presents an important candidate for the genetic improvement of heat-tolerant maize varieties.