Plant material and growth conditions

Plant materials and experimental design was previously described in detail (Rodrigues et al., 2016). Briefly, three widely cropped coffee genotypes from the two main producing species were used: Coffea arabica L. cv. Icatu (an introgressed variety from C. canephora Pierre ex A. Froehner), C. arabica L. cv. IPR108, and C. canephora cv. Conilon Clone 153 (CL153). Potted plants of 1.5 years in age were transferred from a greenhouse (ambient [CO₂]) into walk-in growth chambers (EHHF 10,000, ARALAB, Portugal) differing in air [CO₂] supply: 380 μL CO₂ L⁻¹ (380-plants) or 700 μL CO₂ L⁻¹ (700-plants). Both groups of plants were then grown for 10 months in 28 L pots for ca. 10 months under controlled environmental conditions of temperature (25/20°C, day/night), RH (75%), irradiance (ca. 700–800 μmol m⁻² s⁻¹), photoperiod (12 h), without limitations of nutrients (Ramalho et al., 2013), water and space for root growth, the latter evaluated by visual examination at the end of the experiment, after removing the plants from their pots.

After that 10 months period, air temperature was gradually increased at a rate of 0.5°C day⁻¹, from 25/20°C up to 42/34°C, with a 7 day stabilization at 31/25, 37/30 and 42/34°C to perform several evaluations (Martins et al., 2014, 2016; Rodrigues et al., 2016). Leaf material was collected from newly matured leaves, of both plagiotropic and orthotropic branches of the upper (illuminated) part of the plant, from five to eight plants per genotype and immediately frozen in liquid nitrogen and stored at −80°C until RNA extraction.