The Arabidopsis E3 ubiquitin ligase HOS1 contributes to auxin biosynthesis in the control of hypocotyl elongation

Abstract

Photomorphogenesis is a key developmental process involving numerous developmental and physiological changes in response to light, including inhibition of hypocotyl elongation. Light-dependent hypocotyl development is intensively regulated by all plant hormones. In agreement with this, a number of hormone metabolic and signaling components are involved in the light regulation of plant morphogenesis. Here, we report that the RING finger-containing E3 ubiquitin ligase HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES1 (HOS1) negatively regulates auxin biosynthesis in the control of hypocotyl elongation in Arabidopsis. The HOS1-deficient mutants exhibited a long hypocotyl in light conditions but a short hypocotyl in the dark, as observed in auxin-overproducing mutants. We found that auxin biosynthetic genes, such as YUCCAs (YUCs), TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS 1, and CYP79B2, were up-regulated in the hos1–3 mutant, and endogenous auxin levels were accordingly increased. Furthermore, the long hypocotyl phenotype of light-grown hos1–3 seedlings was rescued by the application of auxin transport inhibitors, 1-naphthylphthalamic acid and 2,3,5-triiodobenzoic acid. Taken together, our data demonstrate that HOS1 modulates auxin biosynthesis and probably links light and auxin signaling in the control of hypocotyl elongation.