No abstract

Plants respond to higher temperatures by the action of heat stress (HS) transcription factors (Hsfs), which control the onset, early response, and long-term acclimation to HS. Members of the HsfA1 subfamily, such as tomato HsfA1a, are the central regulators of HS response, and their activity is fine-tuned by other Hsfs. We identify tomato HsfA7 as capacitor of HsfA1a during the early HS response. Upon a mild temperature increase, HsfA7 is induced in an HsfA1a-dependent manner. The subsequent interaction of the two Hsfs prevents the stabilization of HsfA1a resulting in a negative feedback mechanism. Under prolonged or severe HS, HsfA1a and HsfA7 complexes stimulate the induction of genes required for thermotolerance. Therefore, HsfA7 exhibits a co-repressor mode at mild HS by regulating HsfA1a abundance to moderate the upregulation of HS-responsive genes. HsfA7 undergoes a temperature-dependent transition toward a co-activator of HsfA1a to enhance the acquired thermotolerance capacity of tomato plants.

Alternative splicing (AS) is a major mechanism for gene expression in eukaryotes, increasing proteome diversity but also regulating transcriptome abundance. High temperatures have a strong impact on the splicing profile of many genes and therefore AS is considered as an integral part of heat stress response. While many studies have established a detailed description of the diversity of the RNAome under heat stress in different plant species and stress regimes, little is known on the underlying mechanisms that control this temperature-sensitive process. AS is mainly regulated by the activity of splicing regulators. Changes in the abundance of these proteins through transcription and AS, post-translational modifications and interactions with exonic and intronic cis-elements and core elements of the spliceosomes modulate the outcome of pre-mRNA splicing. As a major part of pre-mRNAs are spliced co-transcriptionally, the chromatin environment along with the RNA polymerase II elongation play a major role in the regulation of pre-mRNA splicing under heat stress conditions. Despite its importance, our understanding on the regulation of heat stress sensitive AS in plants is scarce. In this review, we summarize the current status of knowledge on the regulation of AS in plants under heat stress conditions. We discuss possible implications of different pathways based on results from non-plant systems to provide a perspective for researchers who aim to elucidate the molecular basis of AS under high temperatures.