Inhibition of Brassinosteroid Biosynthesis by Either a dwarf4 Mutation or a Brassinosteroid Biosynthesis Inhibitor Rescues Defects in Tropic Responses of Hypocotyls in the Arabidopsis Mutant nonphototropic hypocotyl 4
- 21 April 2006
- journal article
- Published by Oxford University Press (OUP) in Plant Physiology
- Vol. 141 (2), 456-464
- https://doi.org/10.1104/pp.105.076273
Abstract
The nonphototropic hypocotyl 4 (nph4)/auxin response factor 7 (arf7) mutant of Arabidopsis (Arabidopsis thaliana) is insensitive to auxin and has defects in hypocotyl tropism, hook formation, differential leaf growth, and lateral root formation. To understand an auxin-signaling pathway through NPH4, we carried out screening of suppressor mutants of nph4-103 and obtained a dwarf suppressor mutant, suppressor of nph4 (snp2). snp2 had short hypocotyls in the dark condition and dark green and round leaves, short petioles, and more lateral shoots than the wild type in the light condition. The snp2 phenotypes were rescued by adding brassinolide to the growth medium in both light and dark conditions. Genetic mapping, sequence analysis, and a complementation test indicated that snp2 was a weak allele of DWARF4 (DWF4), which functions in brassinosteroid (BR) biosynthesis. snp2, which was renamed dwf4-101, exhibited photo- and gravitropisms of hypocotyls similar to those of the wild type with a slightly faster response in gravitropism. dwf4-101 almost completely suppressed defects in both tropisms of nph4-103 hypocotyls and completely suppressed hyponastic growth of nph4-103 leaves. Treatment with brassinazole, an inhibitor of BR biosynthesis, also partially rescued the tropic defects in nph4-103. Hypocotyls of nph4-103 were auxin insensitive, whereas hypocotyls of dwf4-101 were more sensitive than those of the wild type. dwf4-101 nph4-103 hypocotyls were as sensitive as those of dwf4-101. Auxin inducibility of massugu 2 (MSG2)/IAA19 gene expression was reduced in nph4-103. mRNA level of MSG2 was reduced in dwf4-101 and dwf4-101 nph4-103, but both mutants exhibited greater auxin inducibility of MSG2 than the wild type. Taken together, dwf4-101 was epistatic to nph4-103. These results strongly suggest that BR deficiency suppresses nph4-103 defects in tropic responses of hypocotyls and differential growth of leaves and that BR negatively regulates tropic responses.Keywords
This publication has 43 references indexed in Scilit:
- Brassinosteroids Stimulate Plant Tropisms through Modulation of Polar Auxin Transport in Brassica and ArabidopsisPlant Cell, 2005
- Interdependency of Brassinosteroid and Auxin Signaling in ArabidopsisPLoS Biology, 2004
- Brassinosteroids Interact with Auxin to Promote Lateral Root Development in ArabidopsisPlant Physiology, 2004
- Brassinolide InducesIAA5, IAA19, and DR5, a Synthetic Auxin Response Element in Arabidopsis, Implying a Cross Talk Point of Brassinosteroid and Auxin SignalingPlant Physiology, 2003
- BES1 Accumulates in the Nucleus in Response to Brassinosteroids to Regulate Gene Expression and Promote Stem ElongationCell, 2002
- Brassinosteroid-Insensitive Dwarf Mutants of Arabidopsis Accumulate BrassinosteroidsPlant Physiology, 1999
- MOLECULAR-GENETIC ANALYSIS OF PLANT CYTOCHROME P450-DEPENDENT MONOOXYGENASESAnnual Review of Plant Physiology and Plant Molecular Biology, 1998
- Brassinosteroids Rescue the Deficiency of CYP90, a Cytochrome P450, Controlling Cell Elongation and De-etiolation in ArabidopsisCell, 1996
- Effect of Brassinolide on Gene Expression in Elongating Soybean EpicotylsPlant Physiology, 1992
- A Revised Medium for Rapid Growth and Bio Assays with Tobacco Tissue CulturesPhysiologia Plantarum, 1962