Abstract
The diversity and environmental plasticity of plant growth results from variations of repetitive modules, such as the basic shoot units made of a leaf, axillary bud, and internode. Internode elongation is regulated both developmentally and in response to environmental conditions, such as light quality, but the integration of internal and environmental signals is poorly understood. Here, we show that the compressed rosette growth habit of Arabidopsis is maintained by the convergent activities of the organ boundary gene ARABIDOPSIS THALIANA HOMEOBOX GENE 1 (ATH1) and of the gibberellin-signaling DELLA genes. Combined loss of ATH1 and DELLA function activated stem development during the vegetative phase and changed the growth habit from rosette to caulescent. Chromatin immunoprecipitation high-throughput sequencing and genetic analysis indicated that ATH1 and the DELLA gene REPRESSOR OF GA1-3 (RGA) converge on the regulation of light responses, including the PHYTOCHROME INTERACTING FACTORS (PIF) pathway, and showed that the ATH1 input is mediated in part by direct activation of BLADE ON PETIOLE (BOP1 and BOP2) genes, whose products destabilize PIF proteins. We conclude that an organ-patterning gene converges with hormone signaling to spatially restrict environmental responses and establish a widespread type of plant architecture.
Highlights
The diversity and environmental plasticity of plant growth results from variations of repetitive modules, such as the basic shoot units made of a leaf, axillary bud, and internode
Vegetative internode elongation under end-of-day FR light treatment (EOD-FR) reverted to wild type in ath1-3 plants transformed with a genomic ARABIDOPSIS THALIANA HOMEOBOX GENE 1 (ATH1) construct tagged with GFP (SI Appendix, Fig. S1), confirming that the enhanced internode elongation was caused by loss of ATH1 function
Of vegetative internode elongation in the ath1-3 global della sextuple mutant, under normal growth conditions and with few other effects on plant architecture (Fig. 3), shows that a relatively simple genetic change can determine the difference between the rosette and caulescent growth habits
Summary
The diversity and environmental plasticity of plant growth results from variations of repetitive modules, such as the basic shoot units made of a leaf, axillary bud, and internode. A striking example of adaptive variation in shoot architecture is the rosette habit, in which very short internodes result in a compact whorl of leaves close to the ground. This architecture is believed to be an adaptation to grazing, drought, and cold environments [3, 4]. The increase in FR light initiates a coordinated developmental response that inhibits branching and prioritizes elongation of the main shoot axis during competition for sunlight [8]. This response is coordinated across multiple shoot organs, it is spatially restricted. PIFs function as a hub to integrate environmental and hormonal signals in the regulation of plant growth [12, 13]
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