Heat-Triggered Transcriptional Reprogramming in Microspores Disrupts Progression of Pollen Development in Brassica napus L.

Rising temperatures due to climate change pose significant threats to global food security, particularly by impacting crop fertility and yield. Despite the known susceptibility of male reproductive development to heat stress, the specific adaptive mechanisms and critical regulatory genes involved in the stage-specific heat stress response in crops are still not well understood. This study examines the impact of acute heat stress on pollen development in Brassica napus (Canola), an essential oilseed crop, with a focus on the uninucleate microspore stage. We demonstrate that a brief exposure to 40{degrees}C during the uninucleate microspore stage results in loss of cellular polarity, failed asymmetric cell division, loss of cytoplasm, and pollen abortion, leading to a significant decline in pollen viability. Transcriptome analysis reveals the complexity of heat-induced transcriptional reprogramming in microspores, identifying 8.1% (6,245) of the expressed genes as responsive to high temperature, with a higher degree of downregulation. Fourteen differentially expressed transcription factors (TFs) belonging to diverse TF families were identified in heat-stressed microspores, with overrepresented target genes. The differential regulation of cell cycle control genes in heat-stressed microspores supports our microscopic observations and details the transcriptional reprogramming underlying the failure of heat-stressed microspores to undergo the first and second pollen mitotic divisions (PMI and PMII), resulting in aberrant pollen development in B. napus. Heat stress disrupts key biological pathways such as transcription, mRNA processing, translational control, protein homeostasis, autophagy, phytohormone signaling, and reactive oxygen species (ROS) homeostasis. Heat stress alters the intricate network of multiple signaling pathways, potentially disrupting the regulatory pathways underlying pollen development, with evident crosstalk underscoring the complexity of the heat stress response in pollen development. These findings underscore the critical vulnerability of the microspore stage to heat stress in Canola. Understanding the identified heat-responsive genes and regulatory networks provides valuable insights for breeding climate-resilient Canola varieties, thereby contributing to global food security amidst changing climatic conditions. HighlightsO_LIAcute heat stress during microspore stage in Brassica napus disrupts pollen development. C_LIO_LIHeat stress induces complex transcriptional reprogramming in microspores, with higher degree of downregulation. C_LIO_LITranscriptional control, RNA processing, coordination of protein homeostasis and translational control is altered in heat-stressed microspores C_LIO_LIMisregulation of cell cycle control genes supports the loss of cellular polarity and failure to undergo asymmetric cell division in heat stressed microspores. C_LI