Molecular signatures of heat tolerance in an Australian alpine plant during moderate warming

Abstract

Understanding the molecular mechanisms of heat tolerance could help to predict the impacts of climate change on our native flora. However, much of our current understanding is derived from Arabidopsis thaliana and select crops exposed to short and intense periods of heat stress. Here, we characterise the transcriptomic response of Wahlenbergia ceracea, a perennial herb found in Australias subalpine regions, to sustained moderate warming. We contrasted responses between relatively heat-tolerant and heat-sensitive lines grown under cool (24/15 {o}C day/night) or warm (30/20 {o}C) temperatures. We observed that sustained warming up-regulated genes related to RNA regulation, including modification and splicing, and down-regulated genes associated with photosynthesis and plastid organization. Interestingly, heat-tolerant lines demonstrated a more pronounced repression of photosynthesis-associated genes, compared to heat-sensitive lines, suggesting that the regulation of the light-harvesting machinery may contribute to photosystem thermal tolerance. Co-expression analyses revealed only weak module-level correlations with direct measures of thermal tolerance. However, stronger associations were evident with chlorophyll content and photosynthetic efficiency, which might indirectly influence thermal tolerance. Prediction of transcription factors targeting warming-responsive genes implicated hormone signaling networks, especially ethylene, in contributing to differences in thermal tolerance. In conclusion, we present genomic resources for transcriptome analyses in W. ceracea and highlight the contrasting gene regulatory patterns between relatively heat-tolerant and heat-sensitive W. ceracea lines experiencing sustained moderate warming.