2.1 Preparation and growth of potato plants expressing cyanobacterial Fld
Construction of the pCAMBIA2200 vector encoding plastid-targeted Fld from Anabaena PCC7119 (pfld ) has been described elsewhere (Tognetti et al. 2006). Briefly, a DNA sequence encoding the chloroplast transit peptide of pea ferredoxin-NADP+reductase (FNR) was fused in-frame to the 5’-end of the AnabaenaPCC7119 fld gene and placed under control of the cauliflower mosaic virus (CaMV) 35S promoter to allow for constitutive expression and plastid targeting in transformed plants (Supplementary Figure S1a). Potato plants (S. tuberosum cv Solara) were transformed by agroinfiltration (Rocha-Sosa et al., 1989) to generate Stpfldlines (for S. tuberosum p lastidic Fld , Supplementary Figure S1a). The presence of Fld in cleared leaf extracts was evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblot detection with specific antisera (Mayta et al. 2019). Plants were propagated in vitro according to Rocha-Sosa et al. (1989), transferred to soil, and grown at 400 μmol photons m-2 s-1, a 16-h photoperiod, 25/22°C and a relative humidity of 80% (growth chamber conditions).
For short-term drought assays, tuber slices of similar sizes corresponding to the various lines were planted in 3-L soil pots. Plants were watered to 100% field capacity (FiC) for 30 days and then subjected to drought by water withdrawal under growth chamber conditions.
For long-term drought treatments, tuber slices of WT andStpfld 252 lines were planted in 15-L soil pots, watered to 100% FiC for the first 30 days of growth. By that time, plants were beginning to set tubers. Watering was interrupted until the soil reached 40% FiC and watered again to 70% FiC. This procedure was repeated until plants were harvested, 120 days post germination (Supplementary Figure S2).