ARS | Publication request: Physiological and genetic characterization of end-of-day far-red light response in maize seedlings

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 28, 2010
Publication Date: July 28, 2010
Citation: Dubois, P., Olsefski, G.T., Hoekenga, O., Flint Garcia, S.A., Brutnell, T. 2010. Physiological and genetic characterization of end-of-day far-red light response in maize seedlings. Plant Physiology. 10.1104/pp.110.159830.

Interpretive Summary: The dramatic gains in maize production over the last 60 years are due to a combination of factors. Breeding efforts have made some improvement to per plant grain yield; however the majority of genetic gain to yield per unit area originates from increasing planting density. Maintaining or increasing yield under high density planting requires an increased tolerance to competition and shading effects from neighboring plants. This implies that light signaling pathways such as the shade avoidance syndrome have been the target of selection. We examined the shade avoidance syndrome using seedling maize plants grown under controlled conditions. We clarified the importance of red light receptors and several plant hormones to shade avoidance. We used genetic methods to identify several chromosomal regions that contain genes important for regulating shade avoidance. This information should lead to an increased understanding of shade avoidance in maize and cultivars that can permit even greater increases in stand density and thus yield per unit area.

Technical Abstract: Yield gains observed in maize hybrids are primarily associated with increased tolerance to high planting density rather than grain yield per plant, and suggest that components of light signaling such as the shade avoidance syndrome (SAS) were the target of selection. To gain a better understanding of the SAS in maize, an end-of-day far-red (EOD-FR) seedling assay mimicking developmental responses observed in dense vegetations was developed. The assay was confirmed to trigger a phytochrome-mediated photoreversible low fluence response. A survey of 28 genetically diverse inbreds established distinctive elongation responses based on their classification. Light signaling mutants phyB1, phyB2, phyB1 phyB2 double and elm1 further detailed the central role played by the phytochrome photoreceptors in mediating the SAS during seedling development. The downstream regulation of the SAS by gibberellins was investigated and suggests a tissue-specific dosage of the hormone. A quantitative trait loci (QTL) analysis using the intermated B73 x Mo17 (IBM) population simultaneously identified two QTLs (bins 4.09 for 1st leaf sheath and 9.03 for mesocotyl) using two different traits: elongation under EOD-FR and ratio of elongation between EOD-FR and control treatments. A B73 near isogenic line (NIL) containing a teosinte introgression at the 9.03 interval displayed significantly higher SAS responses than B73 for all traits measured. The analysis failed to identify members of the phytochrome gene family, suggesting that variations between the two parents lay further downstream in the light signal transduction pathway.