Protective Responses at the Biochemical and Molecular Level Differ between a Coffea arabica L. Hybrid and Its Parental Genotypes to Supra-Optimal Temperatures and Elevated Air [CO2]

Abstract

Climate changes with global warming associated with rising atmospheric [CO2] can strongly impact crop performance, including coffee, which is one of the most world’s traded agricultural commodities. Therefore, it is of utmost importance to understand the mechanisms of heat tolerance and the potential role of elevated air CO2 (eCO2) in the coffee plant response, particularly regarding the antioxidant and other protective mechanisms, which are crucial for coffee plant acclimation. For that, plants of Coffea arabica cv. Geisha 3, cv. Marsellesa and their hybrid (Geisha 3 × Marsellesa) were grown for 2 years at 25/20 °C (day/night), under 400 (ambient CO2, aCO2) or 700 µL (elevated CO2, eCO2) CO2 L−1, and then gradually submitted to a temperature increase up to 42/30 °C, followed by recovery periods of 4 (Rec4) and 14 days (Rec14). Heat (37/28 °C and/or 42/30 °C) was the major driver of the response of the studied protective molecules and associated genes in all genotypes. That was the case for carotenoids (mostly neoxanthin and lutein), but the maximal (α + β) carotenes pool was found at 37/28 °C only in Marsellesa. All genes (except VDE) encoding for antioxidative enzymes (catalase, CAT; superoxide dismutases, CuSODs; ascorbate peroxidases, APX) or other protective proteins (HSP70, ELIP, Chape20, Chape60) were strongly up-regulated at 37/28 °C, and, especially, at 42/30 °C, in all genotypes, but with maximal transcription in Hybrid plants. Accordingly, heat greatly stimulated the activity of APX and CAT (all genotypes) and glutathione reductase (Geisha3, Hybrid) but not of SOD. Notably, CAT activity increased even at 42/30 °C, concomitantly with a strongly declined APX activity. Therefore, increased thermotolerance might arise through the reinforcement of some ROS-scavenging enzymes and other protective molecules (HSP70, ELIP, Chape20, Chape60). Plants showed low responsiveness to single eCO2 under unstressed conditions, while heat promoted changes in aCO2 plants. Only eCO2 Marsellesa plants showed greater contents of lutein, the pool of the xanthophyll cycle components (V + A + Z), and β-carotene, compared to aCO2 plants at 42/30 °C. This, together with a lower CAT activity, suggests a lower presence of H2O2, likely also associated with the higher photochemical use of energy under eCO2. An incomplete heat stress recovery seemed evident, especially in aCO2 plants, as judged by the maintenance of the greater expression of all genes in all genotypes and increased levels of zeaxanthin (Marsellesa and Hybrid) relative to their initial controls. Altogether, heat was the main response driver of the addressed protective molecules and genes, whereas eCO2 usually attenuated the heat response and promoted a better recovery. Hybrid plants showed stronger gene expression responses, especially at the highest temperature, when compared to their parental genotypes, but altogether, Marsellesa showed a greater acclimation potential. The reinforcement of antioxidative and other protective molecules are, therefore, useful biomarkers to be included in breeding and selection programs to obtain coffee genotypes to thrive under global warming conditions, thus contributing to improved crop sustainability.

Uncovering the wide protective responses in Coffea spp. leaves to single and superimposed exposure of warming and severe water deficit

“…Water restrictions that promote Ψ pd values below -3.5 MPa are considered to reflect extreme water deficit for coffee trees ( Pinheiro et al., 2004 ; Dubberstein et al., 2020 ; Semedo et al., 2021 ), as it was the case here, with Ψ pd values below -3.7 MPa. In addition, heat constitutes a major response driver for protective plant responses, but causes strong impairments in coffee leaves at both physiological and molecular levels above 37°C ( Rodrigues et al., 2016 ; Dubberstein et al., 2020 ; Marques et al., 2021 ; Vinci et al., 2022 ). Here, not only harsh single drought and heat were implemented, but also their superimposition, a condition that is expected to be even more frequent in natural conditions.…”

“…Greater heat tolerance was also associated with increased carotenoid levels, namely zeaxanthin and lutein, in coffee leaves ( Martins et al., 2016 ; Vinci et al., 2022 ). Here, temperature rise had a much lower global impact on carotenoid changes than did single drought in both cultivars, except for β-carotene.…”

“…Supra-optimal temperatures can constitute a strong response driver of APX, CAT, and GR (but not of SOD) activities in some C. arabica cultivars ( Vinci et al., 2022 ). This highlight a cultivar-dependent response, since our findings revealed that temperatures up to 37/28°C promoted only APX (CL153) and GR (Icatu) activities, which declined at 42/30°C for both cultivars, as also found in Martins et al.…”

“…Carotenoid (Car) contents were assessed using frozen leaf discs (each 0.5 cm 2 ) cut under the growth chamber conditions. All procedures were carried out exactly as previously described in detail for leaf coffee samples ( Vinci et al., 2022 ), with minor adjustments. Briefly, after extraction in aqueous 90% acetone (v/v), and sample processing and filtration (13 mm, nylon), the separation of the pigments was achieved through a reverse phase HPLC analysis using an end-capped C18, 5 µm Spherisorb ODS 2 column (250 mm × 4.6 mm).…”

Overexpression of Water-Responsive Genes Promoted by Elevated CO2 Reduces ROS and Enhances Drought Tolerance in Coffea Species

“…This suggests the action of three mechanisms involved in drought acclimation: (i) activation of antioxidant activities to scavenge the excessive amount of ROS and reduce oxidative damage in plants, including enzymes (e.g., catalase, superoxide dismutases, peroxidases) and non-enzymatic molecules (e.g., ascorbic acid, α-tocopherol, raffinose family oligosaccharides), in agreement with studies from other plants [ 40 , 41 ]; (ii) antioxidative mechanisms complemented with thermal dissipation mechanisms (e.g., photoprotective carotenoids) and changes in the cyclic electron flow (CEF) to protect the photosystem (PS) I and/or II. In fact, (i) and (ii) are transversally found in resilient Coffea genotypes as response mechanisms to drought [ 12 , 26 ], heat [ 42 , 43 , 44 ], cold [ 45 , 46 ], and high irradiance [ 47 , 48 ] stresses. Additionally, the activation of other molecules, such as aquaporins reported here in Icatu and in previous studies involving other C. arabica genotypes [ 49 ] or the heat shock protein 70 kDa as reported also in other Coffea studies [ 39 , 50 ].…”