Abstract
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.
Highlights
High temperatures cause large morphological, physiological, and biochemical effects limiting plant growth and productivity [44,45]. They have a major impact on plant transcriptomes resulting in a high number of differentially expressed genes (DEGs) when compared to other stresses, the extent and composition vary widely between species [46]
We found that supra-optimal temperatures triggered specific transcriptomic changes in two coffee genotypes, belonging to different species
At 37 ◦ C we found an enrichment in the up-regulation of thylakoid, photosystem, and photosynthesis in both species and under CO2 conditions (Figure 5A), in line with previous results demonstrating the intrinsic ability of these plants to maintain the photosynthetic activity up to 37 ◦ C, regardless of air CO2 but with a clear negative impact at 42 ◦ C [14,30]
Summary
Temperature and carbon dioxide (CO2 ) are major drivers of climate change affecting global crop production [1,2,3]. It is not surprising that many crop improvement programs focus on the development of climate-smart crops resilient to climate change [4]. High temperatures cause physiological, biochemical, and molecular changes affecting key biological processes, such as photosynthesis, by reducing electron transport, NADPH and ATP synthesis, and ribulose-bisphosphate carboxylase (RuBisCO) activity while increasing the production of H2 O2 [7,8,9]. At the other extreme, elevated CO2 (eCO2 ) was found to improve the physiological status and to mitigate the adverse effects of high temperatures in different species, increasing photosynthesis in most
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