Unraveling molecular thermotolerance mechanisms in the wild rice species Oryza australiensis.

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conclusionOryza australiensis combines unique constitutive and inducible responses to heat stress, revealing novel mechanisms and candidate genes putatively involved in thermotolerance for improving cultivated rice's resilience Heat stress negatively impacts plant growth, reproduction, and productivity, posing a growing threat to crop yields under climate change. Understanding thermotolerance mechanisms is critical for developing resilient crops. Oryza australiensis, a wild rice species native to Australia, exhibits greater heat tolerance than the cultivated Oryza sativa, though the molecular basis remains unclear. Here, we investigated comparative heat stress responses and recovery in both species. Our data show that O. australiensis maintained higher expression of Calvin-Benson-Bassham cycle genes under heat stress, consistent with its ability to sustain photosynthesis at elevated temperatures. Genes involved in C4 metabolism showed constitutively higher expression in O. australiensis, suggesting traits of a C3-C4 intermediate species. While both species down-regulated carbohydrate metabolism genes under heat, transcript levels remained higher in O. australiensis. Notably, only O. sativa accumulated sucrose under stress, implying differences in carbon partitioning between the species. We also identified differentially induced genes in O. australiensis related to protein folding, including specific heat shock proteins, alongside reduced expression of calmodulin-related signaling genes. During recovery, only O. australiensis up-regulated thionin genes, indicating a possible link between defense peptides and abiotic stress response. Additionally, several genes with unknown functions were uniquely regulated, highlighting novel candidates for further investigation. Together, these findings suggest that O. australiensis combines constitutive and inducible responses to manage heat stress and represents a valuable genetic resource for enhancing thermotolerance in cultivated rice, a key trait in a changing climate.