Asymmetric auxin distribution and root tropisms (Plant Cell Physiol.) ($)

The asymmetric distribution of the phytohormone auxin is essential for tropic responses of seed plants but it is unclear if this distribution is essential for root negative phototropism as well. To understand the role of auxin distribution in root negative phototropism in Arabidopsis, Kimura and colleagues used pharmacological and genetic analyses of wildtype, auxin biosynthesis mutants and auxin receptor mutants to show that polar auxin transport and auxin biosynthesis are critical for root gravitropism but not root phototropism. However, TIR1/AFB auxin receptors and ARF transcriptional factors do play a minor role in root phototropism. Nevertheless, this paper describes that phototropic responses are induced by a process that doesn’t require asymmetric auxin distribution in the roots of Arabidopsis. (Summary by  Julia Miller) (Plant Cell Physiol.) 10.1093/pcp/pcy018