Touch-induced changes in Arabidopsis morphology dependent on gibberellin breakdown.

Touch can lead to a reduction in plant growth and a delay in flowering time. Touch-induced changes in plant morphology, termed thigmomorphogenesis, have been shown to depend on the phytohormone jasmonate(1). However, touch-induced phenotypes are also reminiscent of plants deficient in the phytohormone gibberellin(2). Here we assess the effect of touch on wild-type Arabidopsis plants and mutants deficient in gibberellin signalling. We show that touch leads to stunted growth and delayed flowering in wild-type plants, as expected. These touch-induced changes in morphology are accompanied by a reduction in gibberellin levels, and can be reversed through the application of a bioactive form of gibberellin. We further show that touch induces the expression of AtGA2ox7, which encodes an enzyme involved in gibberellin catabolism. Arabidopsis ga2ox7 loss-of-function mutants do not respond to touch, suggesting that this gene is a key regulator of thigmomorphogenesis. We conclude that touch-induced changes in Arabidopsis morphology depend on gibberellin catabolism. Given that AtGA2ox7 helps to confer resistance to salt stress, and that touch can increase plant resistance to pathogens, we suggest that gibberellin catabolism could be targeted to improve plant resistance to abiotic and biotic stress.