The effects of DELLAs on growth change with developmental stage and brassinosteroid levels |
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Authors: | Jodi L Stewart Lilley Yinbo Gan Ian A Graham Jennifer L Nemhauser |
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Institution: | 1. Department of Biology, University of Washington, , Seattle, WA, 98195‐1800 USA;2. College of Agriculture and Biotechnology, Zhejiang University, , Hangzhou, 310029 China;3. Department of Biology, Centre for Novel Agricultural Products, University of York, , York, YO10 5DD UK |
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Abstract: | There are two stages in photomorphogenesis. First, seedlings detect light and open their cotyledons. Second, seedlings optimize their light environment by controlled elongation of the seedling stem or hypocotyl. In this study, we used time‐lapse imaging to investigate the relationship between the brassinosteroid (BR) and gibberellin (GA) hormones across both stages of photomorphogenesis. During the transition between one stage and the other, growth promotion by BRs and GAs switched from an additive to a synergistic relationship. Molecular genetic analysis revealed unexpected roles for known participants in the GA pathway during this period. Members of the DELLA family could either repress or enhance BR growth responses, depending on developmental stage. At the transition point for seedling growth dynamics, the BR and GA pathways had opposite effects on DELLA protein levels. In contrast to GA‐induced DELLA degradation, BR treatments increased the levels of REPRESSOR of ga1‐3 (RGA) and mimicked the molecular effects of stabilizing DELLAs. In addition, DELLAs showed complex regulation of genes involved in BR biosynthesis, implicating them in BR homeostasis. Growth promotion by GA alone depended on the PHYTOCHROME INTERACTING FACTOR (PIF) family of master growth regulators. The effects of BR, including the synergistic effects with GA, were largely independent of PIFs. These results point to a multi‐level, dynamic relationship between the BR and GA pathways. |
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Keywords: | brassinosteroids gibberellins
Arabidopsis thaliana
photomorphogenesis PIFs |
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