A Transcriptomic Approach to Understanding the Combined Impacts of Supra-Optimal Temperatures and CO2 Revealed Different Responses in the Polyploid Coffea arabica and Its Diploid Progenitor C. canephora

Understanding the effect of extreme temperatures and elevated air (CO2) is crucial for mitigating the impacts of the coffee industry. In this work, leaf transcriptomic changes were evaluated in the diploid C. canephora and its polyploid C. arabica, grown at 25 °C and at two supra-optimal temperatures (37 °C, 42 °C), under ambient (aCO2) or elevated air CO2 (eCO2). Both species expressed fewer genes as temperature rose, although a high number of differentially expressed genes (DEGs) were observed, especially at 42 °C. An enrichment analysis revealed that the two species reacted differently to the high temperatures but with an overall up-regulation of the photosynthetic machinery until 37 °C. Although eCO2 helped to release stress, 42 °C had a severe impact on both species. A total of 667 photosynthetic and biochemical related-DEGs were altered with high temperatures and eCO2, which may be used as key probe genes in future studies. This was mostly felt in C. arabica, where genes related to ribulose-bisphosphate carboxylase (RuBisCO) activity, chlorophyll a-b binding, and the reaction centres of photosystems I and II were down-regulated, especially under 42°C, regardless of CO2. Transcriptomic changes showed that both species were strongly affected by the highest temperature, although they can endure higher temperatures (37 °C) than previously assumed.

探明极端温度与大气二氧化碳（CO₂）浓度升高的影响，对于减缓咖啡产业所受冲击至关重要。本研究针对二倍体刚果咖啡（C. canephora）及其多倍体阿拉比卡咖啡（C. arabica）的叶片转录组变化展开分析：供试材料分别在环境CO₂（aCO₂）与高浓度CO₂（eCO₂）条件下，于25℃以及两个超适宜生长温度（37℃、42℃）中培养。随着温度升高，两个物种的表达基因总数均有所减少，但同时检测到大量差异表达基因（DEGs），在42℃时尤为显著。富集分析结果显示，两个物种对高温的响应模式存在差异，但在37℃及以下温度时，二者的光合系统整体呈现上调表达。尽管高浓度CO₂可帮助缓解胁迫，但42℃仍对两个物种造成了严重冲击。本研究共筛选得到667个与光合作用及生化过程相关的差异表达基因，这些基因会因高温与高浓度CO₂发生表达量改变，可作为未来相关研究的关键探针基因。该现象在阿拉比卡咖啡（C. arabica）中表现最为明显：无论CO₂浓度如何，当处于42℃条件时，其与核酮糖二磷酸羧化酶（RuBisCO）活性、叶绿素a/b结合以及光系统I、II反应中心相关的基因均呈现下调表达。转录组分析结果表明，两个物种均受到极端高温的强烈影响，但它们可耐受的最高温度（37℃）较此前学界认知有所提升。