Author contributions
Hendrik Swiegers, Barbara Karpinska and Yan Hu undertook all the experimental work. Hendrik Swiegers analysed all the data and prepared the figures for the manuscript. Ian Dodd oversaw the studies on phytohormones and helped to prepare the manuscript. Anna-Maria Botha co-supervised Hendrik Swiegers, discussed the data and helped to prepare the manuscript. Christine Foyer designed the studies, discussed the data and wrote the manuscript.