Ethylene directs auxin to control root cell expansion.

Root morphogenesis is controlled by the regulation of cell division and expansion. We isolated an allele of the eto1 ethylene overproducer as a suppressor of the auxin-resistant mutant ibr5, prompting an examination of crosstalk between the phytohormones auxin and ethylene in control of root epidermal cell elongation and root hair elongation. We examined the interaction of eto1 with mutants that have reduced auxin response or transport and found that ethylene overproduction partially restored auxin responsiveness to these mutants. In addition, we found that the effects of endogenous ethylene on root cell expansion in eto1 seedlings were partially impeded by dampening auxin signaling, and were fully suppressed by blocking auxin influx. These data provide insight into the interaction between these two key plant hormones, and suggest that endogenous ethylene directs auxin to control root cell expansion.