Abstract
Crop biomass and yield are tightly linked to how the light signaling network translates information about the environment into allocation of resources, including photosynthates. Once activated, the phytochrome (phy) class of photoreceptors signal and re-deploy carbon resources to alter growth, plant architecture, and reproductive timing. Most of the previous characterization of the light-modulated growth program has been performed in the reference plant Arabidopsis thaliana. Here, we use Brassica rapa as a crop model to test for conservation of the phytochrome-carbon network. In response to elevated levels of CO2, B. rapa seedlings showed increases in hypocotyl length, shoot and root fresh weight, and the number of lateral roots. All of these responses were dependent on nitrogen and polar auxin transport. In addition, we identified putative B. rapa orthologs of PhyB and isolated two nonsense alleles. BrphyB mutants had significantly decreased or absent CO2-stimulated growth responses. Mutant seedlings also showed misregulation of auxin-dependent genes and genes involved in chloroplast development. Adult mutant plants had reduced chlorophyll levels, photosynthetic rate, stomatal index, and seed yield. These findings support a recently proposed holistic role for phytochromes in regulating resource allocation, biomass production, and metabolic state in the developing plant.
Highlights
Crop biomass and yield are tightly linked to how the light signaling network translates information about the environment into allocation of resources, including photosynthates
High CO2 conditions increased hypocotyl length for seedlings grown on standard medium by 37% (Fig. 1A; Supplementary Fig. S1; P < 0.001)
Climate change and the resultant shifts in temperature, atmospheric composition, and precipitation present a critical challenge for plant life on Earth
Summary
Crop biomass and yield are tightly linked to how the light signaling network translates information about the environment into allocation of resources, including photosynthates. In response to elevated levels of CO2, B. rapa seedlings showed increases in hypocotyl length, shoot and root fresh weight, and the number of lateral roots. All of these responses were dependent on nitrogen and polar auxin transport. Adult mutant plants had reduced chlorophyll levels, photosynthetic rate, stomatal index, and seed yield. These findings support a recently proposed holistic role for phytochromes in regulating resource allocation, biomass production, and metabolic state in the developing plant. When carbon levels are increased by treatment with sugars or elevated CO2 in laboratory conditions, Arabidopsis thaliana seedlings produce more lateral roots (MacGregor et al, 2008; Lilley et al, 2012; Hachiya et al, 2014). Understanding the molecular targets of elevated CO2, in addition to knowledge of how these targets impact biomass allocation, could provide guidance for crop breeding and management practices to optimize future yields
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