Ectopic expression of a hot pepper bZIP-like transcription factor in potato enhances drought tolerance without decreasing tuber yield

Over-expression of group A bZIP transcription factor genes in plants improves abiotic stress tolerance but usually reduces yields. Thus, there have been several efforts to overcome yield penalty in transgenic plants. In this study, we characterized that expression of the hot pepper (Capsicum annuum) gene CaBZ1, which encodes a group S bZIP transcription factor, was induced by salt and osmotic stress as well as abscisic acid (ABA). Transgenic potato (Solanum tuberosum) plants over-expressing CaBZ1 exhibited reduced rates of water loss and faster stomatal closure than non transgenic potato plants under drought and ABA treatment conditions. CaBZ1 over-expression in transgenic potato increased the expression of ABA- and stress-related genes (such as CYP707A1, CBF and NAC-like genes) and improved drought stress tolerance. Interestingly, over-expression of CaBZ1 in potato did not produce undesirable growth phenotypes in major agricultural traits such as plant height, leaf size and tuber formation under normal growth conditions. The transgenic potato plants also had higher tuber yields than non transgenic potato plants under drought stress conditions. Thus, CaBZ1 may be useful for improving drought tolerance in tuber crops. This might be the first report of the production of transgenic potato with improved tuber yields under drought conditions.